SDSU GENERAL PARASITOLOGY: 467

PARTICIPANTS OF A TYPICAL IMMUNE RESPONSE


CENTRAL HUMORAL CHARACTERS IN A PRIMARY IMMUNOLOGICAL RESPONSE

Antigens = sluffed or excreted molecules (primarily proteins) from infectious agents

Antibodies = secreted receptors which bind to antigens

 

Antibodies (immunoglobulins) are proteins that are initially borne on the surface of B-lymphocytes and secreted by plasma cells.  The basic antibody molecule consists of 4 polypeptide chains: 2 identical light chains and 2 identical heavy chains.  These 2 chains are held together into the shape of a "Y" by disulfide and hydrogen bonds.  The amino acid sequence toward the end of the "Y" are quite variable (for both heavy and light chains).  This variable (Fab) region of the antibody determines with which antigen the antibody will bind to.  The remainder of the antibody (Fc) is known as the constant region.  The heavy chains may be any of 5 types, and constitutes the 5 different types of antibodies present in mammalian systems: IgM, IgG, IgA, IgD and IgE.  Each of these 5 classes have slightly different roles in the immune response.  

 


CELLULAR PARTICIPANTS IN A PRIMARY RESPONSE

a3.       B-cells - transform into plasma cells once they are stimulated by an antigen

b3.       Plasma cells - produce specific antibodies once stimulated by the appropriate antibody

c3.       T-cells - helps coordinate antibody production in B-cells (by presenting the antigen to the B-cells; it also helps coordinate the inflammatory response to large parasites by secreting interleukins

d3.       Macrophage - "eats" antigens, and presents them to T-cells (in a proper form); also "eats" protozoan parasites that are coated with antibodies

immuncls.gif

Cellular participants in the immune response develop from a common multipotential stem cell found in bone marrow. Developed B- cells are are released from the bone marrow into the bloodstream or lymph vessels. When they come in contact with appropriate antigens, the B-cells differentiate into plasma cells. Plasma B- cells secrete antibodies, while memory B cells provide lasting immunity. Precursor T-cells migrate from the bone marrow to the thymus gland to mature. As these cells are then released into the blood stream and lymph vessels, they differentiate biochemically and functionally into T4 helper/inducer cells, and intoT8 cytotoxic/suppressor cells. Macrophage development begins in the bone marrow as myeloid stem cells which enter into the blood stream. Mature macrophages eventually migrate to the skin, spleen and lymph nodes, where they wait to be stimulated by antigens.

 

Immunological "Bullets"

  1. Antibody directed agglutination of foreign cells immobilize protozoan parasites

  2. Compliment - cascading system of proteins which can be cytolytic and play a central role in the regulation of inflammation

  3. Macrophage phagocytosis of protozoan parasites

  4. Lyosome-carrying cells (eosinophils, cytotoxic T-cells, etc.)

 

 



immunrsp.gif

 

TYPICAL IMMUNOLOGICAL RESPONSE TO PARASITES

  1. Antigens (+) are continually sluffed from the parasite

  2. The antigens bind to the receptors (Y) of their antigen-specific B-cell population (B)

  3. These antigens are then phagocytosed into the B-cell,

  4. partially digested portions of the antigen are presented to the surface of the B-cell attached to a Class II major histocompatibility complex coded protein (h)

  5. Antigens are also phagocytosed by specific macrophages (Mh or Mc),

  6. partially digested and presented to the macrophage surface attached either to a Class I (Mc= Macrophage for the cytotoxic T-cells) or

  7. a Class II (Mh= Macrophage for the helper T-cells) major histocompatibility complex.

  8. The antigens associated with each macrophage (Mc or Mh) are then presented to the receptors (w or u) of their specific T-cell population (Tci= immature cytotoxic T-cell; Thi= immature helper T-cell)

  9. Once the antigen is presented to the immature cytotoxic T-cell and the immature helper T-cell, they proliferate and differentiate into mature cytotoxic T-cells and mature helper T-cells.

  10. Mature helper T-cells bind to those B-cells that are directed against the same antigen.

  11. The binding of the helper T-cell to the B-cell causes the B-cell to proliferate and differentiate into plasma cells. As plasma cell, these cell continually secrete their "receptors" as antibodies.

  12. Some of the mature cells (helper and cytotoxic) revert back to memory cells (Tci(m) and Tci(m)).

  13. Mature cytotoxic cells bind to the parasite and attempt to kill it through a variety of means.

  14. Interleukins secreted by the helper T-cell regulates the proliferation and differentiation of the cytotoxic cells relative to the presence or absence of antigens.