THE BODY’S DEFENSE

CHAPTER 43

Immunity• Invertebrates have nonspecific

systems• Plants have molecular recognition of

pathways to defend against pathogens; leads to destruction of infected cells

• Vertebrates have nonspecific and nonheritable defense systems

• Mammals have nonspecific, humoral and cell mediated.

Figure 43.4 The human lymphatic system

Figure 43.0 Specialized lymphocytes attacking a cancer cell

Figure 43.2 First-line respiratory defenses. Inside the lining of the trachea.

Yellow cells are ciliated. Orange cells secrete mucus.

•Innate immunity is present before any exposure to pathogens and is effective from the time of birth

• It involves nonspecific responses to pathogens

• Innate immunity consists of external barriers plus internal cellular and chemical defenses

•Acquired immunity, or adaptive immunity, develops after exposure to agents such as microbes, toxins, or other foreign substances

• It involves a very specific response to pathogens

NONSPECIFIC DEFENSE

•Skin•Mucus•Secretions

CELLS:Nonspecific

•Neutrophils - engulf microbes (phagocytosis); self-destruct after destroy microbes

•Macrophages - can migrate into tissues and engulf microbes

•Esinophils - destroy parasitic worms

•Natural killer cells - destroy viral-infected cells

Figure 43.x1 Anabaena (a blue-green algae that makes a toxin, which causes cell death)

phagocytosed by a human neutrophil

Anabaena

Figure 43.3x Macrophage

Figure 43.3 Phagocytosis by a macrophage

Bacilli

Pseudopodia of macrophage

INFLAMMATORY RESPONSE

•Arterioles dilate to increase blood flow to damaged area

• Increased WBC in damaged area

•Histamine and prostaglandins released to dilate arterioles

•Chemokines - chemical signals for cells to follow

Fig. 43-8-3

Pathogen Splinter

Macrophage

Mast cell

Chemicalsignals

Capillary

Phagocytic cellRed blood cells

Fluid

Phagocytosis

SPECIFIC DEFENSE

•Response is to a specific microbe

•Antigen - foreign molecule•Antibody - proteins made to

attach to specific antigens

CELLS:Specific

•B lymphocytes - develop in bone marrow; differentiate into plasma cells which secrete antibodies; also make memory cells

•T lymphocytes - develop in thymus; activate B cells and other WBC; also make memory cells

Figure 43.8 The development of lymphocytes

Figure 43.8x B lymphocyte

Figure 43.6 Clonal selection

•Primary immune response - first exposure; 10 - 17 days; make antibodies

•Secondary immune response - already been exposed; 2 - 7 days; memory cells make antibodies quickly

Figure 43.7 Immunological memory

TOLERANCE FOR SELF•Major histocompatibility complex (MHC) on cells–Class I MHC on all nucleated cells

–Class II MHC on macrophages, B cells and activated T cells

–Biochemical fingerprint–As your cells develop, if fingerprint is wrong then cell death occurs

–MHC molecules cradle foreign antigens. They present the antigen to other cells.•MHC I presents antigens to Cytotoxic T cells which kill bad cells

•MHC II presents antigens to Helper T cells

–Cells that present antigens are called antigen presenting cells (APCs). These include macrophages and B cells.

Figure 43.9 The interaction of T cells with MHC molecules

HUMORAL VS. CELL MEDIATED IMMUNITY

•Humoral - B cells activated by free antigens (free bacteria, toxins, viruses)

•Cell mediated - depends on T cells; active against cells infected with viruses and bacteria; as well as free fungi, protozoa, and worms

Fig. 43-16

Humoral (antibody-mediated) immune response

B cell

Plasma cells

Cell-mediated immune response

Key

Stimulates

Gives rise to

+

+

++

+

+

+Memory B cells

Antigen (1st exposure)

Engulfed by

Antigen-presenting cell

MemoryHelper T cells

Helper T cell Cytotoxic T cell

MemoryCytotoxic T cells

ActiveCytotoxic T cells

Antigen (2nd exposure)

Secretedantibodies

Defend against extracellular pathogens by binding to antigens,thereby neutralizing pathogens or making them better targetsfor phagocytes and complement proteins.

Defend against intracellular pathogensand cancer by binding to and lysing theinfected cells or cancer cells.

+

+ +

Immune System Players•Antigen presenting cells (APC) include B cells and macrophages

•Present antigen on class II MHC

•T helper cell (Th) binds to MHC II with antigen

•CD4 on Th cell holds APC cell and Th cell together

•Th then activates T cytotoxic cells

•T cytotoxic cells can then lyse infected cells

Figure 43.11 The central role of helper T cells: a closer look

Figure 43.12a The functioning of cytotoxic T cells

Figure 43.12b A cytotoxic T cell has lysed a cancer cell

ANTIBODY PRODUCTION

•T-dependent antigens - B cell must be activated by Th cell; most protein antigens

•T-independent antigens - directly stimulate B cells to make antibodies; mostly polysaccharide antigens

Figure 43.13 Humoral response to a T-dependent antigen (Layer 3)

ANITBODY MEDIATED DISPOSAL OF ANITGEN

•Opsonization - many antibodies bound to antigen enhance macrophage phagocytosis

•Agglutination - antibodies attach to many antigens; clumping them together to enhance phagocytosis

Figure 43.16 Effector mechanisms of humoral immunity

ACTIVE IMMUNITY

•Depends on response of infected person’s immune system

•May be artificially induced by vaccinations

Figure 43.x2 Vaccination

PASSIVE IMMUNITY

•Antibodies transferred from one individual to another

•Some antibodies can move across placenta to baby in pregnant women

•Nursing

HEALTH AND DISEASE•Review ABO blood types

and Rh•MHC causes tissue and

organ rejections•In bone marrow transplants,

donated marrow (with WBC) will react against recipient

•Allergies - overproduction of certain antibodies causes histamine to be released–Runny nose–Teary eyes–Smooth muscle contractions = hard breathing

Figure 43.x4 Alternaria spores, a cause of allergies in humans

•Anaphylactic shock - life-threatening reaction; abrupt dilation of arteries causes serious drop in blood pressure

•Autoimmune diseases - attack own body–Lupus, rheumatoid arthritis, MS

• Immunodeficiency Diseases –Severe combined immunodeficiency (SCID), Hodgkin’s

Figure 43.x3 X-ray of hands with arthritis

•AIDS - acquired immunodeficiency syndrome–Two major strain: HIV I and HIV II

–Bind to CD4 and therefore Th cells

–Insert its RNA and reverse transcriptase makes viral DNA that is inserted into host’s DNA

–Exists as provirus so antibodies can’t get rid of it easily

–Mutates often

–May cause Th cell death

–HIV positive = presence of HIV antibodies

Figure 43.19 A T cell infected with HIV

Figure 43.19x1 HIV on a lymphocyte, detail

Figure 43.20 The stages of HIV infection

Figure 43.x5 AIDS posters