Acquired Immunity: Humoral Response Distinction of Humoral versus Cell-Mediated Acquired Immunity...

Acquired Immunity: Humoral Response

• Distinction of Humoral versus Cell-Mediated Acquired Immunity

• Antigens and Antigenic Determinants: Non-self and MHC proteins

• Cell Types of the Humoral Response and How they Develop

• B and T cell receptors and immunglobulins (antibodies)

• Antibody Structure and Classes

• Activation of B cells and Clonal Selection

• Immunity and Secondary Response Time

• Antibody Actions

• Passive and Active Immunity

• Monoclonal Antibodies

• Cell-Mediated Immune System: T cells, Grafting

Body Defenses: Innate and AcquiredDefense Systems of the Body

Non-specific defense system (Innate Immune System)

• Mechanisms protect against a variety of invaders

• Responds immediately to protect body from foreign materials

(Innate immunity)

Specific defense system (Acquired Immune System: Humoral and Cell-Mediated)

• Specific defense is required for each type of invader

• Also known generically as just “the immune system”

Nonspecific (Innate) Body DefensesMechanical, Chemical, and Competitive Barriers

Saliva and tears destroy bacteria because they contain lysozyme.

Skin produces acidic sebum to limit bacterial growth and sebum fatty acids are fungistatic

, urine, blood, saliva

Nitric oxide (NO) released by macrophages inhibit ATP production

Iron-binding proteins in blood block microbial reproduction

Inflammation

Figure 16.9c, d

Serum proteins activated in a cascade.

Results:

• Opsonization

• Chemotaxis

• Transmembrane channel formation in cells tagged by antibodies (causing cytolysis)

• Triggers inflammation

The Complement System

Figure 16.10

Body Defenses: Innate and AcquiredDefense Systems of the Body

Non-specific defense system (Innate Immune System)

• Mechanisms protect against a variety of invaders

• Responds immediately to protect body from foreign materials

(Innate immunity)

Specific defense system (Acquired Immune System: Humoral and Cell-Mediated)

• Specific defense is required for each type of invader

• Also known generically as just “the immune system”

Acquired Immune System – Third Line of Defense

Antigen specific – recognizes and acts against particular foreign substances

Systemic – not restricted to the initial infection site

Has memory – recognizes and mounts a stronger attack on previously encountered pathogens

The Acquired Immune System is:

Types of Acquired Immunity

1. Humoral Immunity

• Antibody-mediated immunity in blood and lymph

• Cells produce chemicals for defense

2. Cellular immunity of the Cell-Mediated Immune System

• Cell-mediated immunity

• Cells target virally infected cells

Antigens (Nonself) Antigen: Any substance capable of

exciting the immune system and provoking an immune response

Examples of common antigens

• Foreign proteins

• Nucleic acids

• Large carbohydrates

• Some lipids

• Pollen grains

• Microorganisms

Antigenic determinants: substances (like glycoproteins) on the surface of antigens to which the immune system actually responds Receptor in the

immune system that "fits" the

antigenic determinant

Antigen

Antigens

Self-Antigens Human cells have many

surface proteins called major histocompatability complexes (MHC).

All body cells have MHC Class I proteins.

Our immune cells do not attack our own proteins

Our cells in another person’s body can trigger an immune response because they are foreign

• Restricts donors for transplants

Allergies Many small molecules (called

haptens or incomplete antigens) are not antigenic, but link up with our own proteins

The immune system may recognize and respond to a carrier-hapten combination

This immune response can be harmful rather than protective because it can attack small molecules mounted on our own cells or small molecules normally found in the environment that bind to carriers allergy or autoimmunity

Humoral (Innate) Immune Response

• Distinction of Humoral/Innate versus Cell-Mediate Response



• B and T cell receptors and immunglobulines (antibodies)







Cells of the Immune System Lymphocytes

• Originate from hemocytoblasts in the red bone marrow

• B lymphocytes become immunocompetent in the bone marrow

• T lymphocytes become immunocompetent in the thymus

Macrophages (certain mature granulocytes)

• Arise from monocytes

• Become widely distributed in lymphoid organs

Development of Lymphocytes

T cell maturation and "education"

B Cell Receptors, T Cell Receptors, and Immunoglobulins

B cell

Secreted (Exported) Immunoglobulin or

Antibody (Same V and C Regions as in B cell

receptors)

Variable (binding

) regions

Receptors on T Cells

Constant

regions

Receptors on B cells

T cell

Immunoglobulins and Receptors Bind To Antigens

Agglutination of antigens

Different Classes of Antibodies

B Cell Activation and Clonal Selection

Humoral

immunity movie

Secondary Response (Immunity)

Figure 12.13

Results of Antibody Binding to Antigen• Agglutination (coralling of the invader)

• Precipitation (removal of soluble antigens from blood and lymph)

• Neutralization (blocking antigen's activity and binding)

• Opsonization (faciliating macrophage phagocytosis)

• Tagging, complement fixation, and transmembrane channel formation (lysis of pathogen)

Agglutination Precipitation (soluble antigens)

Transmembrane channel

formation and lysis

Antibody Function movie

Active vs Passive Immunity Active Immunity

• Your B cells encounter antigens and produce antibodies

• Active immunity can be naturally or artificially acquired (e.g via vaccination)

Passive Immunity

• Antibodies are obtained from someone else

o Conferred naturally from a mother to her fetus

o Conferred artificially from immune serum or gamma globulin

• Immunological memory does not occur

• Protection provided by “borrowed antibodies”

Monoclonal Antibodies Antibodies prepared for

clinical testing or diagnostic services

Produced from descendents of a single cell line

Examples of uses for monoclonal antibodies

• Diagnosis of pregnancy

• Treatment after exposure to hepatitis and rabies

• HIV/AIDS detection in ELISA Assays

Cell Mediated Immune Response

Players in the Cell Mediated Response

Activation of Cytotoxic T and B cells via TH cells

Other T cells and their function

Tissue grafting

Cellular (Cell-Mediated) Immune Response

1. Antigens must be presented by macrophages to an immunocompetent T cell (antigen presentation)

2. T cells must recognize non-self antigen and self MHC proteins (double recognition)

3. After antigen binding, clones form as with B cells, but different classes of cells are produced

Activation of T and B Cells Through TH cells

MHC "self"

identifying

protein

Types of T Cells Cytotoxic T (Tc) cells

• Specialize in killing infected cells

• Insert a toxic chemical (perforin)

Helper T (TH) cells

• Recruit other cells to fight the invaders

• Interact directly with B cells

Suppressor T cells

• Release chemicals to suppress the activity of T and B cells

• Stop the immune response to prevent uncontrolled activity

A few members of each clone are memory cells

Helper t cells animation

Cytotoxic t cells animation

Summary of B Cell Activation

B cells can be activated directly by antigen or from a TH cell activated by an antigen-presenting macrophage

Summary of the Immune Response

Organ Transplants and Rejection Major types of grafts

• Autografts – tissue transplanted from one site to another on the same person

Hey buddy, my patch of skin is damaged! Can I have your autograft?

• Isografts – tissue grafts from an identical person (identical twin)

• Allografts – tissue taken from an unrelated person (sometimes successful)

• Xenografts – tissue taken from a different animal species (rarely successful)

Acquired Immunity: Humoral Response Distinction of Humoral versus Cell-Mediated Acquired Immunity...

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