Specific acquired immunityThe Immune Response
Chapter 16 and 17
Nester 4th. Ed.
Characteristics of Specific Acquired Immunity (The Immune Response)
Recognizing self from non-self (foreign) Protects the body from specific non-self
organisms and substances It is an induced response; our body cells are
trained or taught to attack which things Typically a specific immune response against one
pathogen will be ineffective against a different pathogen, sometimes even a closely related but still different pathogen
Characteristics of Specific Acquired Immunity (The Immune Response)
Specific immunity is acquired (not innate)• response has memory• also called anamnestic or secondary response• quicker/more effective than primary at
subsequent exposures
Primary and secondary response
Figure 16.11
Lag period 10 days to 2 weeks
Specific Immunity
Also known as adaptive immunity or acquired immunity, active or passive
Normally comes into play when innate or non-specific immunity can't handle the problem.
Mechanisms of the Immune Response
Two types of specific immune responses; humoral and cell mediated
Humoral immunity• B-lymphocytes (develop in bone marrow)
proliferate and differentiated into plasma cells produces Y-shaped molecules called Antibodies
Cell mediated immunity• T-lymphocytes (mature in Thymus)
• Effector T cytotoxic cells
• Effector T helper cells
CellularImmunity
Effector T-helper cell
B cell
Extracellular antigen
Activates B cellsthat bind antigen
HumoralImmunity
CellularImmunity
Effector T-helper cell
B cell
Extracellular antigen
Activates B cellsthat bind antigen
HumoralImmunity
CellularImmunity
Effector T-helper cell
Proliferation and differentiationof activated B cell
Plasma cell
Memory cell+
B cell
Extracellular antigen
Proliferation and differentiationof activated B cell
Activates B cellsthat bind antigen
HumoralImmunity
CellularImmunity
Plasma cellAntibodyproduction
Memory cell
Effector T-helper cell
+
B cell
Extracellular antigen
Proliferation and differentiationof activated B cell
Activates B cellsthat bind antigen
HumoralImmunity
CellularImmunity
Plasma cellAntibodyproduction
Antibodiesbind antigen
Memory cell
Effector T-helper cell
+
B cell
Extracellular antigen
Proliferation and differentiationof activated B cell
Activates B cellsthat bind antigen
HumoralImmunity
CellularImmunity
Plasma cellAntibodyproduction
Antibodiesbind antigen
Memory cell
Effector T-helper cell
Host cells routinelypresent samples ofcytoplasmic proteins.
Virus
+
B cell
Extracellular antigen
Proliferation and differentiationof activated B cell
Activates B cellsthat bind antigen
HumoralImmunity
CellularImmunity
Plasma cellAntibodyproduction
Antibodiesbind antigen
Memory cell
Effector T-cytotoxic cell
Effector T-helper cell
Stimulates effector T-cytotoxiccells that bind antigen
Host cells routinelypresent samples ofcytoplasmic proteins.
Virus
+
B cell
Extracellular antigen
Proliferation and differentiationof activated B cell
Activates B cellsthat bind antigen
HumoralImmunity
CellularImmunity
Plasma cellAntibodyproduction
Antibodiesbind antigen
Memory cell
Effector T-cytotoxic cell
Effector T-helper cell
Stimulates effector T-cytotoxiccells that bind antigen
Destroys infected host cells Those cells presenting viralproteins or other abnormalproteins that signify dangerare destroyed.
Host cells routinelypresent samples ofcytoplasmic proteins.
Virus
+
B cell
Extracellular antigen
Proliferation and differentiationof activated B cell
Activates B cellsthat bind antigen
HumoralImmunity
CellularImmunity
Plasma cellAntibodyproduction
Antibodiesbind antigen
Memory cell
Effector T-cytotoxic cell
Effector T-helper cell
Activates macrophages thathave engulfed antigen
Stimulates effector T-cytotoxiccells that bind antigen
Destroys infected host cells
Activated macrophage
Those cells presenting viralproteins or other abnormalproteins that signify dangerare destroyed.
Host cells routinelypresent samples ofcytoplasmic proteins.
Virus
+
Molecules involved in the Immune Response Antigens Antibodies Major Histocompatibility Complex
Molecules
Molecules involved in the Immune Response -Antigens
Any molecule that react specifically with an antibody or a lymphocyte.
Foreign to the host Immunogens are antigens that elicit an immune
response in a given situation High molecular weight-at least 10,000 daltons
Molecules involved in the Immune Response -Antigens
Complex molecules
• protein, polysaccharide - best Ag
• lipid, nucleic acid - not good at all
• lipoprotein, nucleic acid with protein - average Ag
Molecules involved in the Immune Response -Antigens Have antigenic determinants (epitopes)
• Antibody binds to antigenic determinant small region of antigen
• small portions of the whole antigen molecule• equivalent of 10-25 amino acids long• large antigens may have 100 or more epitopes• Figure 16.1
Molecules involved in the Immune Response -Antigens Hapten
• Small molecules with a molecular mass under 5000 dalton make poor antigens by themselves
• Small molecules (haptens) can become immunogenic when combined with a larger carrier protein
• small molecular weight • acts as an antigenic determinant• example -penicillin (350 Dalton)
Molecules involved in the Immune Response -Antigens Exogenous antigens
• By inhalation, ingestion, or injection (cell wall, flagella etc)
• E.g. dust and pollen etc. Endogenous antigens
• Altered self antigens• E.g. denaturation of proteins
• Addition of viral antigens to cells• Viruses, protozoa and fungi which multiply
inside the host cells
Molecules involved in the Immune Response - Antibodies Immunoglobulins
• glycoproteins• recognize epitopes of antigens
• Figure 16.1
• 5 classes - meaning types• IgM, IgG, IgA, IgD, IgE
• Table 16.1 - Each class has a function
Molecular weight
Arms
Stem
Disulfide bonds
Crystallizable
Variable amino acids
Antigen binding site
Class of antibody
Figure 16.3, Page 397
Molecules involved in the Immune Response - Antibodies Generic structure - Y
• Figure 16. 3• Figure 16. 4• heavy chains- constant region and variable region• light chains- constant region and variable region• hinges• Constant region of heavy chain defines the class
of immunoglobulin
Molecules involved in the Immune Response - Antibodies Generic structure
• Variable regions of the light and heavy chains together determines the specificity of antibody to antigen
• disulfide bridges• Fab• Fc• antigen binding site
Molecules involved in the Immune Response - Antibodies
• complementarity• Figure 16.5• antigen binding site of antibody and specific
antigenic epitope• Fit must be precise• Bonds hold the antibody and antigen are
non-covalent, weak and have short range
Protective Outcome of Antibody-Antigen Binding (Figure 16.5)
Precipitation by precipitin Agglutination by agglutinin Opsonization by opsonin- Complement-fixation and activation Immobilization and prevention of
adherence Neutralization Antibody Dependent Cellular Cytotoxicity
Toxin or virus coated with antibody is prevented from interacting with a healthy cell
Antibodies + antigen = clumps for phagocytic cells e.g. IgM
Antigen + antibod trigger classical pathway of complement cascasde
Multiple IgG molecules bind to a cell, cell becomes target for destruction by natural killer cells
NK cells deliver granules containing protease and perforin
IgG
Compliment system
Regulatory proteins halt the process inactivate C3b
Regulatory proteins are not associated with microbial surfaces
C3a and C5a→induce changes in endothelial cells and mast cells →↑ vascular permeability
C5a attracts phagocytes
C3b binds to foreign material called opsonized, C3b called opsonins
Immunoglobulin G (IgG) Accounts for about 80% to 85% of the total
serum immunoglobulin Is a single Y shape - 2 antigen binding sites Is found in circulation Is the first and most abundant circulating
class produced during the secondary response
Reaches high levels and has a long half- life 21 days
Is part of long term immunity
Functions of IgG
Works best against infectious agents that reach the blood
Types of reactions• agglutination• precipitation• neutralization• opsonization • complement fixation and activation
Functions of IgG
Crosses the placenta from the mother to provide immunity for the new born• (Fig 16.7)
Premature infants have a problem with infection since they do not get this passive transfer of immunity
Also present in colostrum
Infant antibodies3 to 6 months
Immunoglobulin M (IgM)
Accounts for 5% to 13% of circulating antibodies
Is the first Ab produced during primary response to an antigen
Is made of 5 Y shapes - pentamer• joined with a J chain and disulfide bridges• 10 antigen binding sites• Is found in circulation only- too big to get out
Function of IgM
good for agglutination and precipitation• phagocytes pick up large agglutinated clumps
more efficiently
best at activating complement (classical pathway)
removes microorganisms early in the course of an infection
only Ab made against polysaccharide Ag’s
Immunoglobulin A (IgA) Accounts for 10% to 13% of antibodies Is in monomer form in circulation Is in dimer form on mucous membranes called
secretory IgA (sIgA)• Produced by plasma cells –B cells reside in the
mucosal-associated lymphoid tissue (MALT)• Composed of two monomeric antibody subunits
connected by a J-chain• Found on mucous membranes of genitointestinal,
genitourinary and respiratory tracts• Found in saliva, tears and breast milk• Ab is transported to the surface of the mucosal lining• Secretory component helps keep enzymes from
degrading the Ab
Functions of IgA
inhibits adherence of microorganisms to host cells
prevents colonization and therefore infection
Neutralizes toxins and viruses protects the breast-fed infant’s GI tract from
infection
Immunoglobulin D (IgD)
Accounts for less than 1% of all serum immunoglobulins
Is in monomer form Binds to B-cells by its Fc end May be involved in the maturation of B-
cells
Immunoglobulin E (IgE)
Is in monomer form Barely detectable in blood Bound to mast cells and basophils by its Fc
end Is not free in circulation Bound cells releases a mixture of potent
chemicals histamine, cytokines etc that contributes to inflammatory response
Functions of IgE
IgE has beneficial effects.• IgE binds to parasitic worms
• they are then expelled from the GI tract
• IgE is the second line of defense at mucous membranes
• if org. gets past the IgA in the surface, IgE gets it in the tissue
Functions of IgE
IgE has beneficial effects.• IgE and IgG function in ADCC
• antibody dependent cellular cytotoxicity
• eosinophils bind IgE and IgG by their Fc fragments
• the Ab variable ends bind to the parasites• eosinophils release anti-microbial proteins• eosinophils have a peroxidase-halide anti-
microbial system
Major Histocompatibility Complex Molecules
Major histocompatibility antigens First time in humans these antigens were
identified on leukocytes and were named human leukocyte antigens (HLA)
Major histocompatability complex (MHC) clusters of genes
In humans MHC is located on each copy of chromosome 6
Major Histocompatibility Complex Molecules
Major Histocompatibility Complex (MHC) is a set of molecules displayed on cell surfaces that are responsible for lymphocyte recognition and “antigen presentation”
MHC molecules control the immune response through recognition of "self" and "non-self" and, consequently, serve as targets in transplantation rejection
Class I and Class II MHC molecules
Molecules of the Immune Response-Major Histocompatibility Complex Molecules (Fig 16.16)
MHC class I molecules
• are on all nucleated cells
• not on RBC’s
• interact with Ag fragments of 8-10 amino acids long
• present Ag to T-cytotoxic lymphocytes (CD8 cells)
(surface protein cluster of differentiation)
• Endogenous antigens
MHC class II molecules• are on macrophages, B
cells and dendritic cells• interact with Ag
fragments of 12-25 amino acids long
• present Ag to T-helper lymphocytes (CD4 cells)
• Exogenous antigens
Antigen binding groove Exogenous antigens
Endogenous antigens
Molecules of the Immune Response-Major Histocompatibility Complex Molecules Cluster of genes
• on chromosome 6• code for histocompatibility antigens
• on surfaces of many cell types
• in humans, called human leukocyte antigens (HLA)
• involved in transplant rejection
Also called the HLA gene cluster
Molecules of the Immune Response-Major Histocompatibility Complex Molecules
Human leukocyte antigens (HLA) • Proteins located on the surface of
white blood cells which play an important role in our body's immune response to foreign substances
• Vary from person to person• These antigens are also used to determine the
suitability of a match between a donor and a recipient. Patients and potential donors have their white blood cells tested for three antigens - HLA-A, -B and –DR
• Each individual has two sets of these antigens, one set inherited from each parent.
Molecules of the Immune Response-Major Histocompatibility Complex Molecules
Other reasons for importance of MHC molecules• cell to cell contact needed for an immune
response• recognition of self or foreign substance (non-
self)• accept self• dispose of foreign material
Tissues involved in the Specific Immune Response- Lymphoid System
Lymphatic vessels
Lymphoid tissues
Tissues involved in the Specific Immune Response- Lymphoid Tissues
Primary Lymphoid organs• bone marrow
• thymus
Secondary lymphoid organs• Organs
• adenoids
• tonsils
• spleen
• lymph nodes
• Diffuse tissues• MALT
• SALT
Cells Involved in the Specific Immune Response Macrophages Lymphocytes
Cells Involved in the Specific Immune Response - Macrophages Non specific cells that are involved in the
killing of bacteria and the phagocytosis of garbage in the tissues
In the specific immune response they are important due to their role in the processing and presenting of antigens to the lymphocytes.
Cells Involved in the Specific Immune Response - Macrophages Antigen Processing
• To a Cytotoxic T cell• To a Helper T cell
Cells Involved in the Specific Immune Response - Lymphocytes Development of Lymphocytes
Figure 15.3, Page 377
Clonal selection
Specific response of lymphocytes to an antigen
This process gives rise to a population of clones of the original cell ‘Clonal selection”
Clonal Selection of Lymphocytes
See Figure 16.8tp://highered.mcgraw-hill.com/sites/0072919248/student_view0/chapter16/animations.html#
Development of Lymphocytes
Descriptive terms for lymphocytes• Immature lymphocytes
• not fully developed their antigen specific receptors
• Naïve lymphocytes • have antigen receptors but have not yet encountered
the antigen
• Activated lymphocytes • have bound to antigen and have received signals
from another cell regarding danger and able to proliferate
Development of Lymphocytes
Descriptive terms for lymphocytes
• Effector lymphocytes • descendents of activated lymphocytes that
are armed with the ability to produce specific cytokines, endowed with effector functions TH and TC
• Memory lymphocytes • long-lived descendents of activated
lymphocytes, responsible for the speed and effectiveness of the secondary response
B lymphocytes and the Antibody Response
Molecules on the outside of B lymphocytes• B cell receptors (BCR), MHC Class II
molecules and MHC I molecules Response to T-dependent antigens Response to T-independent antigens Characteristics of the primary immune response Characteristics of the secondary immune
response
1) B cell receptor binds to antigen
Antigen
B cell receptor
1) B cell receptor binds to antigen 2) B cell internalizes antigen
Antigen
B cell receptor
1) B cell receptor binds to antigen 2) B cell internalizes antigen
3) B cell degrades antigen into peptide fragments, then presents them in the groove of MHC class II molecules that reside on the B-cell surface.
Antigen
B cell receptor
Antigen fragment presentedby MHC class II molecule
4) If the T-cell receptor of an effector T-helper cell binds to one of the fragments, then cytokines are delivered to the B cell, initiating the process of clonal expansion.
1) B cell receptor binds to antigen 2) B cell internalizes antigen
3) B cell degrades antigen into peptide fragments, then presents them in the groove of MHC class II molecules that reside on the B-cell surface.
Cytokine delivery
Antigen
T-cell receptor
B cell receptor
Antigen fragment presentedby MHC class II molecule T cells antigen-specific
receptors
B lymphocytes and the Antibody Response Response to T-dependent antigens
• Antigens are generally proteins• Antigen binds to a B-cell receptor• B-cell needs to respond• Before that B-cell requires confirmation by an
effector T-helper cell that antigen truly merit a response
• B-cell begin dividing and differentiating and finally producing antibodies
B lymphocytes and the Antibody Response Response to T-independent antigens
• Stimulate an antibody response by activating B cells without the aid of effector T cells
• E.g. polysaccharides (capsules of Streptoccocus pneumoniae and Hemophilus influenzae) that have numerous identical evenly spaced epitopes
• Lipopolysaccharide (LPS) outer membrane of Gram-negative bacteria
• Clusters of B-cells receptors binds the antigen simultaneously, which leads to B-cells activation without T-helper cells
Figure 19.14, Page 476
Lipopolysaccharide also functions as a T-independent antigen
B lymphocytes and the Antibody Response
Characteristics of the primary immune response• Lag period (10 days to 2 weeks)
• Affinity maturation
• B-cells that binds to an antigen most tightly and for longest duration are most likely to proliferate
• Class switching
• Under the direction of cytokines, some B cells become programmed to produce antibodies other than IgM. Most commonly switch to IgG production
• Memory cells• Memory B cells persist in the body for years and in
sufficient numbers
B lymphocytes and the Antibody Response Characteristics of the secondary immune
response• Memory B cells are responsible for swift and
effective response• IgG immunoglobulins• IgG antibody can circulate in body for years
allowing protection against specific antigens
Characteristics of secondary response• Memory cells responsible for swift effective
reaction of secondary response• Often eliminate invaders before noticeable harm is
done
• Vaccine exploits phenomenon of immunologic memory
• Some memory B cells will differentiate into plasma cells
• Results in rapid production of antibodies
B Lymphocyte and Antibody Response
T-Lymphocytes
T lymphocytes• Molecules on the outside of all T cells
-T-cell receptors TCR’s, MHC Class I
molecules• Types of T cells
• Tc cells (cytotoxic) - CD8
• Th cells (helper) - CD4
• T memory cells
T-Lymphocytes
T lymphocytes• T Cell Receptors (Figure 16-15)
T cell receptors, Figure 16.15, p 407
One
One
One antigen binding site
T-Lymphocytes
Types of effector T cells• T cytotoxic cells TC
• T helper cells TH
• T memory cells
T lymphocytes T cytotoxic cells (Figure 16.17)
• have the CD8 molecule on its outside surface • recognizes an antigen that is specific for the
shape of the TCR• has to have the antigen presented to it by an
antigen presenting cell (macrophage and B cell) in combination with a MHC class I molecule
• Release several pre-formed cytotoxins (perforin and proteases)
• Apoptosis, apoptotic cells are quickly removed by macrophages
T-Lymphocytes
Role of T cells different from B cells• T cells never produce antibodies• T cells armed with effectors that interact
directly with antigen• T cell receptor does not react with free antigen
– Antigen must be present by APC
Antigen recognition by T cells
Figure 16.17, Page 408
T lymphocytes T cytotoxic cells (continued)
• Recognizes antigens on the outside of the cell• Endogenous antigens
– virus infected cells
– tumor cells
– tissue transplant cells
• Mechanisms of killing-Figure 16.18• apoptosis triggered by TC cell cytokines
• cytokines
Virally infected "self" cellpresents peptides fromcytoplasmic proteins in thegroove of MHC class I molecules
Virus
(b)
Virally infected "self" cellpresents peptides fromcytoplasmic proteins in thegroove of MHC class I molecules
Effector T-cytotoxic cell recognizes viralantigens presented by infected "self" cell
Virus
(b)
Virally infected "self" cellpresents peptides fromcytoplasmic proteins in thegroove of MHC class I molecules
Effector T-cytotoxic cell recognizes viralantigens presented by infected "self" cell
Virus
Virally infected "self" cellundergoes apoptosis
Effector T-cytotoxic cell delivers preformedcytotoxins to the infected "self" cell and producescytokines that allows neighboring cells to becomemore vigilant against intracellular pathogens
Secretion of cytokines
Targeted deliveryof cytotoxins thatinduce apoptosis
(b)
T lymphocytes
T-helper cells (Figure 16.17)• Have the CD4 marker on the outside• Antigen is presented by a specialized group of
cells called antigen-presenting cells (APCs)• APCs have MHC class II molecules (B cells,
dendritic cells and macrophages)• Exogenous antigens
Role of TH cells in B cell activation
• If TH cell encounters B cell bearing peptide: MHC calls II complex
• TH cell responds by producing cytokines
• B cell is activated in response to cytokine stimulation
• B cell proliferates and undergoes class switching
• Also drives formation of B memory cells
T LymphocytesAntigen Recognition and Response
Role of TH cells in macrophage activation
• Macrophages routinely engulf invading microbes resistant to lysosomal killing
• TH cells recognize macrophage with engulfed microbes resistant to killing
• TH cells activate macrophages by delivering cytokines that induce more potent destructive mechanisms
T LymphocytesAntigen Recognition and Response
Macrophage engulfs materials
Macrophage engulfs materials
Macrophage degrades proteins inphagosome into peptide fragments
Peptide fragments fromengulfed material are presentedby MHC class II molecules
Macrophage engulfs materials
Macrophage degrades proteins inphagosome into peptide fragments
T-cell receptor
CD4
Peptide fragments fromengulfed material are presentedby MHC class II molecules
Secretion of cytokines
Effector T-helper cell recognizesa peptide being presented by themacrophage and respondsby activating the macrophage
Targeted deliveryof cytotoxins activatemacrophage
Macrophage engulfs materials
Macrophage degrades proteins inphagosome into peptide fragments
Activated macrophage
•Enlarges
•Cell metabolism increases
•Lysosomes increases
•Nitric oxide potent antimicrobial chemical
T lymphocytes Effector T-helper cell
• Th1
• Antigen presented by macrophages• Effector Th1• Outcome
– Macrophages activation– release wide variety of cytokines– stimulate natural killer cells– Increase production of monocytes in bone marrow– Recruit macrophages at the site– Make phagocytic cell to adhere or exist from blood
vessels• Th2
• Antigen presented by B cells• Active in the antibody response
T Lymphocytes
Antigen presentation by a macrophage to a T-helper Cell (Figure 16.19)
T lymphocytes
Role of Dendritic Cells in T-Cell Activation (Figure 16.20)
Activation of T cells
Figure 16.20, Page 411
•Surface proteins
•Flashing red lights signifies danger
Natural Killer Cells Natural killer cells (NK cells)
• large, granular lymphocytes• lack markers of T or B lymphocytes
• probably related to T cells
• but lack TCR’s
• lack antigenic specificity
Natural Killer Cells
Natural killer cells (NK cells)• Antibody Dependent Cellular Cytotoxicity
(antibodies coat antigen, NK cells recognizes target by Fc receptors)
• Release granules containing perforin and proteases directly to the target cell
• Recognize and destroy host cells without MHC class I molecules
Lymphocyte Development
Negative selection of Self-reactive B cells
Positive and negative selection of self reactive T cells
Lymphocyte Development
Negative selection of Self-reactive B cells• Process of eliminating lymphocytes including
B-cells that recognize “self” molecules• Called clonal deletion• Occurs in bone marrow and secondary
lymphoid organs• Apoptosis• Failure to eliminate such B-cells leads to
production of autoantibodies
Lymphocyte Development
Positive and negative selection of self reactive T cells• Positive selection
• Process that permits only those T cells that recognize MHC molecule to some extent to develop further
• Those T cells that show insufficient recognition fail positive selection and are eliminated
• Negative selection• T cells that recognize “self” peptide presented by
MHC molecules are also eliminated
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Secondary lymphoid organs
Mature (naive) T cells
Tissues
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Secondary lymphoid organs
Mature (naive) T cells
Tissues
Dendritic cellsgather antigen
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Secondary lymphoid organs
Mature (naive) T cells
Tissues
Dendritic cellsgather antigen
Travel to secondary lymphoidtissue, developing into antigen-presenting cells; co-stimulatorymolecules are expressed ifantigen represents microbialinvasion or tissue damage.
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Secondary lymphoid organs
Mature (naive) T cells
Tissues
Dendritic cellsgather antigen
Travel to secondary lymphoidtissue, developing into antigen-presenting cells; co-stimulatorymolecules are expressed ifantigen represents microbialinvasion or tissue damage.
Antigen presented by MHC Class Imolecules in the presence ofco-stimulatory molecules activatesnaive T-cytotoxic cells. Naive T-cytotoxic
(CD8) cells
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Secondary lymphoid organs
Mature (naive) T cells
Tissues
Dendritic cellsgather antigen
Travel to secondary lymphoidtissue, developing into antigen-presenting cells; co-stimulatorymolecules are expressed ifantigen represents microbialinvasion or tissue damage.
Antigen presented by MHC Class Imolecules in the presence ofco-stimulatory molecules activatesnaive T-cytotoxic cells. Naive T-cytotoxic
(CD8) cells
Antigen presented by MHC Class IImolecules in the presence ofco-stimulatory molecules activatesnaive T-helper cells
Naive T-helper(CD4) cells
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Secondary lymphoid organs
Mature (naive) T cells
Tissues
Dendritic cellsgather antigen
Travel to secondary lymphoidtissue, developing into antigen-presenting cells; co-stimulatorymolecules are expressed ifantigen represents microbialinvasion or tissue damage.
Antigen presented by MHC Class Imolecules in the presence ofco-stimulatory molecules activatesnaive T-cytotoxic cells. Naive T-cytotoxic
(CD8) cells
Antigen presented by MHC Class IImolecules in the presence ofco-stimulatory molecules activatesnaive T-helper cells
Naive T-helper(CD4) cells
Activation, proliferation,development ofeffector T cell functions
Activation, proliferation,development ofeffector T cell functions
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Secondary lymphoid organs
Mature (naive) T cells
Tissues
Dendritic cellsgather antigen
Travel to secondary lymphoidtissue, developing into antigen-presenting cells; co-stimulatorymolecules are expressed ifantigen represents microbialinvasion or tissue damage.
Antigen presented by MHC Class Imolecules in the presence ofco-stimulatory molecules activatesnaive T-cytotoxic cells. Naive T-cytotoxic
(CD8) cells
Antigen presented by MHC Class IImolecules in the presence ofco-stimulatory molecules activatesnaive T-helper cells
Naive T-helper(CD4) cells
Activation, proliferation,development ofeffector T cell functions
Activation, proliferation,development ofeffector T cell functions
MemoryT-helper cellsEffectorT-helper cells
MemoryT-cytotoxic cellsEffectorT-cytotoxic cells
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Secondary lymphoid organs
Mature (naive) T cells
Tissues
Dendritic cellsgather antigen
Travel to secondary lymphoidtissue, developing into antigen-presenting cells; co-stimulatorymolecules are expressed ifantigen represents microbialinvasion or tissue damage.
Antigen presented by MHC Class Imolecules in the presence ofco-stimulatory molecules activatesnaive T-cytotoxic cells. Naive T-cytotoxic
(CD8) cells
Antigen presented by MHC Class IImolecules in the presence ofco-stimulatory molecules activatesnaive T-helper cells
Naive T-helper(CD4) cells
Activation, proliferation,development ofeffector T cell functions
Activation, proliferation,development ofeffector T cell functions
MemoryT-helper cellsEffectorT-helper cells
MemoryT-cytotoxic cellsEffectorT-cytotoxic cells
Th2 Th1
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Secondary lymphoid organs
Mature (naive) T cells
Tissues
Dendritic cellsgather antigen
Travel to secondary lymphoidtissue, developing into antigen-presenting cells; co-stimulatorymolecules are expressed ifantigen represents microbialinvasion or tissue damage.
Antigen presented by MHC Class Imolecules in the presence ofco-stimulatory molecules activatesnaive T-cytotoxic cells. Naive T-cytotoxic
(CD8) cells
Antigen presented by MHC Class IImolecules in the presence ofco-stimulatory molecules activatesnaive T-helper cells
Naive T-helper(CD4) cells
Activation, proliferation,development ofeffector T cell functions
Activation, proliferation,development ofeffector T cell functions
MemoryT-helper cellsEffectorT-helper cells
MemoryT-cytotoxic cellsEffectorT-cytotoxic cells
Th2 Th1
Free antigen
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Secondary lymphoid organs
Mature (naive) T cells
Tissues
Dendritic cellsgather antigen
Travel to secondary lymphoidtissue, developing into antigen-presenting cells; co-stimulatorymolecules are expressed ifantigen represents microbialinvasion or tissue damage.
Antigen presented by MHC Class Imolecules in the presence ofco-stimulatory molecules activatesnaive T-cytotoxic cells. Naive T-cytotoxic
(CD8) cells
Antigen presented by MHC Class IImolecules in the presence ofco-stimulatory molecules activatesnaive T-helper cells
Naive T-helper(CD4) cells
Activation, proliferation,development ofeffector T cell functions
Activation, proliferation,development ofeffector T cell functions
MemoryT-helper cellsEffectorT-helper cells
MemoryT-cytotoxic cellsEffectorT-cytotoxic cells
Th2 Th1
Free antigenT-dependent antigens
Naive B cells
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Secondary lymphoid organs
Mature (naive) T cells
Tissues
Dendritic cellsgather antigen
Travel to secondary lymphoidtissue, developing into antigen-presenting cells; co-stimulatorymolecules are expressed ifantigen represents microbialinvasion or tissue damage.
Antigen presented by MHC Class Imolecules in the presence ofco-stimulatory molecules activatesnaive T-cytotoxic cells. Naive T-cytotoxic
(CD8) cells
Antigen presented by MHC Class IImolecules in the presence ofco-stimulatory molecules activatesnaive T-helper cells
Naive T-helper(CD4) cells
Activation, proliferation,development ofeffector T cell functions
Activation, proliferation,development ofeffector T cell functions
MemoryT-helper cellsEffectorT-helper cells
MemoryT-cytotoxic cellsEffectorT-cytotoxic cells
Th2 Th1
Free antigenT-dependent antigens
Naive B cells Activation, proliferation, classswitching, affinity maturation
Activates B cellsthat present antigen
Mature (naive) B cells
Tissues Secondary lymphoid organs
Dendritic cellsgather antigen
Travel to secondary lymphoidtissue, developing into antigen-presenting cells; co-stimulatorymolecules are expressed ifantigen represents microbialinvasion or tissue damage.
Antigen presented by MHC Class Imolecules in the presence ofco-stimulatory molecules activatesnaive T-cytotoxic cells.
Antigen presented by MHC Class IImolecules in the presence ofco-stimulatory molecules activatesnaive T-helper cells
T-dependent antigens
Naive T-cytotoxic(CD8) cells Activation, proliferation,
development ofeffector T cell functions
Activation, proliferation,development ofeffector T cell functions
Activation, proliferation, classswitching, affinity maturation
Memory cells
Naive T-helper(CD4) cells
MemoryT-helper cellsEffectorT-helper cells
Activates B cellsthat present antigen
Th2 Th1
MemoryT-cytotoxic cellsEffectorT-cytotoxic cells
Naive B cellsFree antigen
Mature (naive) T cells
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Tissues Secondary lymphoid organs
Dendritic cellsgather antigen
Travel to secondary lymphoidtissue, developing into antigen-presenting cells; co-stimulatorymolecules are expressed ifantigen represents microbialinvasion or tissue damage.
Antigen presented by MHC Class Imolecules in the presence ofco-stimulatory molecules activatesnaive T-cytotoxic cells.
Antigen presented by MHC Class IImolecules in the presence ofco-stimulatory molecules activatesnaive T-helper cells
Plasma cells produce antibody; dependingon site of infection and duration of exposure,the class may be IgM, IgG, IgA, or IgE
T-dependent antigens
Naive T-cytotoxic(CD8) cells Activation, proliferation,
development ofeffector T cell functions
Activation, proliferation,development ofeffector T cell functions
Activation, proliferation, classswitching, affinity maturation
Memory cells
Naive T-helper(CD4) cells
MemoryT-helper cellsEffectorT-helper cells
Activates B cellsthat present antigen
Th2 Th1
MemoryT-cytotoxic cellsEffectorT-cytotoxic cells
Naive B cellsFree antigen
Mature (naive) T cells
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Tissues Secondary lymphoid organs
Dendritic cellsgather antigen
Travel to secondary lymphoidtissue, developing into antigen-presenting cells; co-stimulatorymolecules are expressed ifantigen represents microbialinvasion or tissue damage.
Antigen presented by MHC Class Imolecules in the presence ofco-stimulatory molecules activatesnaive T-cytotoxic cells.
Antigen presented by MHC Class IImolecules in the presence ofco-stimulatory molecules activatesnaive T-helper cells
Plasma cells produce antibody; dependingon site of infection and duration of exposure,the class may be IgM, IgG, IgA, or IgE
T-dependent antigens
Naive T-cytotoxic(CD8) cells Activation, proliferation,
development ofeffector T cell functions
Activation, proliferation,development ofeffector T cell functions
Activation, proliferation, classswitching, affinity maturation
Memory cells
Naive T-helper(CD4) cells
MemoryT-helper cellsEffectorT-helper cells
Activates B cellsthat present antigen
Th2 Th1
MemoryT-cytotoxic cellsEffectorT-cytotoxic cells
Naive B cellsFree antigen
Th 1 cells activate macrophages that presentantigen via MHC class II molecules; also producecytokines that orchestrate other responses
Mature (naive) T cells
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Mature (naive) B cells
Tissues Secondary lymphoid organs
Dendritic cellsgather antigen
Travel to secondary lymphoidtissue, developing into antigen-presenting cells; co-stimulatorymolecules are expressed ifantigen represents microbialinvasion or tissue damage.
Antigen presented by MHC Class Imolecules in the presence ofco-stimulatory molecules activatesnaive T-cytotoxic cells.
Antigen presented by MHC Class IImolecules in the presence ofco-stimulatory molecules activatesnaive T-helper cells
Plasma cells produce antibody; dependingon site of infection and duration of exposure,the class may be IgM, IgG, IgA, or IgE
T-dependent antigens
Naive T-cytotoxic(CD8) cells Activation, proliferation,
development ofeffector T cell functions
Activation, proliferation,development ofeffector T cell functions
Activation, proliferation, classswitching, affinity maturation
Memory cells
Naive T-helper(CD4) cells
MemoryT-helper cellsEffectorT-helper cells
Activates B cellsthat present antigen
Th2 Th1
MemoryT-cytotoxic cellsEffectorT-cytotoxic cells
Naive B cellsFree antigen
Th 1 cells activate macrophages that presentantigen via MHC class II molecules; also producecytokines that orchestrate other responses
Effector T-cytotoxic cells destroy cellsthat presented antigen via MHC class Imolecules; also produce cytokines thatallow neighboring cells to become morevigilant against intracellular pathogen.
Mature (naive) T cells
Primary lymphoid organ(bone marrow)
Immature B cells
Primary lymphoid organ(thymus)
Immature T cells
Top Related