Microbio Lecture 7

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Immunity

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1. Immunity → the ability to specifically counteract foreign organisms or substances
2. Antigens → (Ag) chemical substances that cause the body to produce specific antibodies or sensitized T-cells
3. Antibodies → (Ab) proteins produced by B-cells in response to the presence of an antigen
4. B-cells and T-cells → specialized lymphocytes that play a key role in the immune response

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Two basic types of immunity

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Naturally Acquired Immunity
Artificially Acquired Immunity

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Naturally acquired passive immunity

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1. Ab’s transferred from mother to developing fetus
2. Ab’s transferred to a newborn in colostrum
a. May last for up to several months

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Artificially acquired active immunity

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Immunity resulting from vaccination
May be long lasting

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Artificially acquired passive immunity

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Humoral Ab’s acquired by injection

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The humoral immune system

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1. Ab’s produced by B-cells in response to a specific antigen
2. Defend against bacteria, viruses, & toxins

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Cell-mediated Immunity

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1. Depends on T-cells
2. Does not depend on Ab production
3. A response to intracellular bacteria & viruses as well as multicellular parasites, transplanted tissue, and cancer cells

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Antigenic Determinants / Epitopes

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specific regions on the surface of an Ag that combines with specific Ab

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Hapten

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small mw substance that cannot cause Ab formation unless combined with a carrier molecule

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Antibody / Immunoglobulin

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A protein produced by B-cells in response to an Ag.

Immunoglobulins are found in the gamma-globulin or beta-globulin portion of serum proteins

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Antibody Structure

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1. An Ab has at least two identical Ag-binding sites
2. Valence → the number of Ag-binding sites
3. A single bivalent AB molecule is a monomer
4. Monomers consist of four polypeptide chains → two heavy chains and two light chains

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five major classes of Ab molecules

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IgG
IgM
IgA
IgD
IgE

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Functions of IgG

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Provide naturally acquired passive immunity
Neutralize bacterial toxins
Enhance phagocytosis
Participate in complement fixation

Also, IgG is a monomer

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FUnctions of IgM

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IgM is a pentamer

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IgA Abs

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Monomers, secretory IgA Abs are dimers that protect mucosal surfaces from invasion by pathogens

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Which cells actually secrete antibodies?

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Plasma cells

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Primary response

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Response of the body to first contact with an antigen.

1. Production of IgM
2. Followed by IgFG

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Secondary response

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Anamnestic / memory response
Will result in very high antibody titer
Primarily uses IgG

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Cytokines

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cellular messagners by which cells communicatino with each other

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Examples of cytokines

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1. Interleukins (IL) → serve as communicators between leukocytes
2. Interferons → protect cells against viruses
3. Chemokines → cause leukocytes to move to the site of infection

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Details about T-cells

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T-cells migrate to lymphoid tissue after differentiation in the thymus
1. T-cells differentiate into effector 2. T-cells when stimulated by an Ag
3. Some effector T-cells become memory cells

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Natural Killer cells

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help kill cancerous cells

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Hypersensitivity

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1. Harmful immune reactions → hay fever, transplant rejection, autoimmunity
2. Infection & immunosuppression represent a failure of the immune system
3. Superantigens activate T-cell receptors
4. Hypersensitivity represents an immune response to an Ag that leads to tissue damage

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4 types of hypersensitivity

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1. Types I,II, and III are immediate reactions that are based on humoral immunity
2. Type IV is based on CMI and is a delayed reaction

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Mast cells and basophils

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1. Have granules
2. When we're infected, they degranulate and destroy bad orgs quickly

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Anaphylactic reactions

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Anaphylactic reactions involve the production of IgE Abs which bind to mast cells and basophils (sensitizing the host)

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Cytotoxic Reactions

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-Mediated by IgG or IgM Abs and complement
-Abs are directed toward foreign cells or host cells
-Complement fixation may result in cell lysis
-Macrophages & other cells may also damage the Ab-coated cells

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Rh blood group system

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Rh+, Rh-, exposure to Rh+ during delivery. Then

Prevented by passive immunization of mother with anti-Rh Abs

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Type III Complex Reactions

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1. Immune complex diseases occur when IgG Abs and soluble Ag form small complexes that lodge in the basemembrane of cells
2. Subsequent complement fixation results in an inflammatory response
3. Glomerulonephritis is an example of an immune complex disease

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Type IV Cell - Mediated Reactions

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1. Delayed-type hypersensitivity is primarily due to TD cell proliferation
2. Sensitized T cells secrete cytokines in response to the appropriate Ag
3. Cytokines attract and activate macrophages and initiate tissue damage
4. The tuberculin skin test and allergic contact dermatitis are examples
5. Hypersensitivity to latex in latex gloves also falls into this category

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Autoimmune Diseases

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1. Autoimmunity results from a loss of self-tolerance
2. Self-tolerance occurs during fetal development → T-cells that will target host cells are eliminated (clonal deletion) or inactivated
3. Type I autoimmunity may be due to Abs against infectious agents
4. Type II autoimmunity involves reactions in which Abs react to cell-surface Ags

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Examples of type II autoimmune disease

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Examples of Type II autoimmune disease are Grave’s disease and myasthenia gravis

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Autoimmune disease results from

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A loss of self-tolerance

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B-cells and T-cells

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special types of lymphocytes

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Humoral Immune system

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In the body fluids

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B-cells originate as

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Bone marrow stem cells

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Examples of lymphoid organs

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spleen, lymph nodes

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How do antibodies form?

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1. B-cells exposed to Ag become activated, divide and differentiate into a clone of many effector cells called plasma cells
2. The plasma cells produce Abs that fight the original antigen that activated the B-cell
3. Other activated B-cells instead become memory cells

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What cells are responsible for cell-mediated immunity?

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T-cells

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What do cytokines do?

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They help cells of the immune system communicate with each other