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Immune Processes

Outline

A. Properties of immune system

    a. protection

    b. surveillance

    c. recognition

    d. memory

    e. activation of a variety of response mechanisms

B. Innate and Adaptive Immune Responses

C. Classes and Function of Antibodies

a. Classes of antibodies

b. how antibodies function   

        1. opsonize bacteria (making it easier to be attacked by phagocytes)

        2. bind to receptors on bacteia and viruses preventing them from binding to host cells

        3. fix (activate complement)

        4. bind to exotoxin (thus neutralizing it)

c. Humoral Immunity vs Cellular Immunity

    a. Humoral Immunity

    b. Cellular Immunity

d. Active and Passive Immunity

e. Primary and Secondary Immune Responses

f. Immunogenesis

g. Class I MHC and Class II MHC molecules

Discussion  

    Memory is an important property of the immune system. The first time the immune system encounters a foreign substance (primary response)  it "learns". The second time it encounters the same foreign substance (secondary response) it recalls aspects of the first encounter through both memory T and memory B cells.Because of this memory it is able to respond faster. This is the basis for vaccines.
    When an antigen enters body fluids, both an innate and adaptive response are triggered, the innate response is faster. If antigen penetrates a cell, then the cell can express Class I MHC protein on the surface (in which case killer T cells respond by destroying the infected cell) or it can express Class II MHC protein on the surface (in which case helper T cells are activated either to increase macrophage activity or B cell activity).
    MHC stands for major histocompatibility complex. It is a series of genes that code for proteins unique to each individual. Basically, these genes code for two classes of proteins, referred to as Class I MHC molecules and Class II MHC molecules. Each individual's Class I and Class II MHC proteins differ from other individual's Class I and Class II MHC proteins, the diffrence being genetically determined. These proteins, which are like individual fingerprints, play an important role in enabling the immune system to recognize self from non self. Class II MHC proteins are produced by macrophages and helper T cells. Class I MHC proteins are expressed by virtually all other cells of the body. Class II MHC proteins are used by macrophages in the procesing of antigens for presentation to helper T cells.
    A consideration of immune processes reveals that
1. there is tremendous communication and cooperation between different elements of the immune system. This comunication can lead to modulation, either amplification or suppression of the immune response. It gives direction, or intelligence, to the immune response. communication and cooperation rely heavily on cell surface receptors and chemical messages released by wbc's.
2.There is a great diversity of antibodies and cell surface receptors. The immune system has enough different antibodies and cell surface receptors to match virtually every antigen it might encounter
3. There is an ability to distinguish self from non self , largely through the presence of unique, genetically determined proteins, the Class I and II MHC proteins
4. there is a wide variety of immune mechanisms which, when activated, are capable of destroying antigens

Clinically  

    The pluripotential stem cell is responsible for creating and reconstituting all the cells that circualte in the blood: red bllod cells, platelets and white blood cells. Precursor cells that derive from stem cells can replicate and differentiate at an astounding rate. The average person makes 3- 10 billion platelets, rbcs, neutrophils and lymphocytes in just one hour. The bone marrow can increase this by 10 fold in response to a need. Platelets stay in circulation for one week, rbcs for 120 days and neutrophils for just 8 hours. Hormones can act on the bone marrow to stimulate the pluipotential stem cell. For example, granulocyte colony stimulating factor (G-CSF) can increase production of granulocytes, erythropoietin (produced by renal tissue) can stimulate production of rbc's etc.
    People can be tissue typed. The basis for this tissue typing is a determination of  MHC proteins (virtually unique to each idividual) expressed on the surface of cells. There are seven genes which code for MHC proteins. These genes are located on the short arm of chromosome number 6. These seven genes which are closely linked are deignated HLA-A, HLA-B , HLA-C, HLA-D, HLA-DR, HLA-DQ and HLA-DP. Each of these seven genes have multiple alleles.For example, HLA-A has at least 23 different proteins assciated with it, HLA-B has 47 possible antigens associated with it etc. The possible combination of genes that can be inherited makes for tremendous diversity in the expresion of MHC protiens. It is unlikely that 2 people will have exactly the same set of MHC proteins. ( Historically, the proteins coded for by these genes were first found on the surface of leukocytes and were designated human leukocyte antigens. Hence, the term HLA stuck.  Thus HLA is synonymous with MHC). If a person needs a transplant, then HLA tissue typing is done. . Based on tissue distribution and structure, HLA's have been divided into two groups:
Those derived from Class I MHC
HLA-A, HLA-B , HLA-C

Those derived from Class II MHC
HLA-D, HLA-DR, HLA-DQ, HLA-DP