(Transcribed from Dr. Kalliecharan lectures beginning, 24 Feb 2000 by Brian Buschman)
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Note: For this note set I have not included everything that Dr. Kalli talked about in the lecture. This was written primarily as my personal study aid and made available as a general service. In this set of notes I have left out a number of things, because I know them but you should refer to your lecture notes to be sure you are not missing anything.
There are four distinct properties of the immune system:
1) Specificity
2) Diversity
3) Memory
4) Recognition of self v. non-self
T-lymphocytes stem in the bone marrow and are sent to the thymus to mature and become immunocompetent. They then migrate to peripheral, non-thymic, lymphoid organs to wait until they are needed.
B-lymphocytes are made in the bone marrow where they also become immunocompetent and then migrate directly to peripheral, non-thymic, lymphoid organs.
Cellular immunity is the immune process mediated by the T-lymphocytes where cells are produced and go out to take care of the business themselves.
Humoral immunity is the process that is mediated by B-lymphocytes where the cells produce antibodies that go out to take care of things.
There are five classes of antibodies:
1) IgG are the most abundant, migrate into intercellular spaces and are able to cross the placental barrier.
2) IgA are the secretory Ig. They are bound to Protein J that helps them be resistant to many enzymes. Due to this resistance, they are the secretory proteins that protect the respiratory tract, GI tract and are secreted in breast milk.
3) IgM are a pentamer. They are usually bound to B-cells and assist in the activation of the compliment system.
4) IgD have a unknown function.
5) IgE are bound to mast cells and basophils. They are usually bound and rarely found free. When antigens are encountered the complex releases histamine, leukotrine, heparin, eosinophilic-chemotactic factor (ECF-A). IgE is involved in the mediation of allergic reactions.
Initial contact of an antigen to a B-lymphocyte causes the production of IgM. Later after the second exposure, the mast cells will undergo class switching to produce other classes of antibodies.
B-lymphocytes develop in bone marrow and migrate to non-thymic lymphoid tissues. They then wait until stimulated and proliferate and differentiate into memory B-cells and plasma cells. The plasma cells produce and bind antibodies.
T-lymphocytes originate in bone marrow and migrate to the thymus where they proliferate and become immunocompetent. They then migrate to non-thymic peripheral lymphoid tissue. When stimulated they develop into:
1) Killer (CD-8, cytotoxic) T-cells that work directly on the antigenic cells by using perforins to cause osmolysis and they induce apoptosis.
2) Memory T-cells that wait and cause a rapid response to the second exposure of the same antigen.
3) Suppressor T-cells that regulate the immune responses (both T-cell and B-cell mediated responses).
4) Helper (CD-4) T-cells produce ILs to assist in the binding of B-cells to antigens. AIDS causes the death of these cells therefore inactivating the humeral response.
APCs are derived from the bone marrow and include a number of different cells that reside in different parts of the body.
They first grab the antigen and partially digest it (take a piece off of it). Some pieces are endocytosed and digested in liposomes. The remaining fragments are complexed with MHC II. Antigen fragments that are digested in the cytosol are transported to the ER where they are complexed with MCH I. Both are transported to the plasma membrane.
MHC I interacts with CD-8 T-cells (cytotoxic T-cells) and it is found on the surface of all cells.
MHC II interacts with CD-4 T-cells (helper T-cells) and it is only found on the surface of APCs making them necessary for the activation of humoral immunity.
The MHC complexes are essential to the process as the CD-4 and CD-8 cells are unable to directly recognize the fragment as antigen. They are the immune system’s way of telling the T-cells “here is a piece of antigen, go get it.”
1) Humoral Response:
a) An abnormal cell displays foreign Ag and macrophages bind the Ag.
b) Ag is given to the APC that takes chunk, digests it, complexes it with MHC II.
c) Helper (CD-4) t-cells recognize it, proliferates and begins to make ILs.
d) The ILs help the B-lymphocytes bind the Ag.
e) B-lymphocytes become memory B-cells and plasma cells.
f) Plasma cells make Abs that bind to Ag to make Ab-Ag complex (now jump over to compliment system).
2) Cell Mediated Response:
a) An abnormal cell displays foreign Ag and macrophages bind the Ag.
b) APC takes part of it, digests and complexes it with MHC I.
c) The MHC I is recognized by killer (CD-8 or cytotoxic) T-cells.
d) The cytotoxic T-cells find the antigenic cells and either induce apoptosis or produce perforins which cause osmolysis.
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