1. MHC Molecules
Our immune system has the remarkable ability, and responsibility, of responding appropriately to a wide variety of potential pathogens in our environment.
The proteins that are used as cell-markers to “flag” self from non-self are called MHC molecules, and are coded for by a group of genes called the major histocompatibility complex (MHC).
MHC genes are diverse, and vary greatly from individual to individual.
Our adaptive immune system has the remarkable ability to respond to at least a billion different epitopes
Genetic recombination is the shuffling and rearranging of a few hundred versions of several small gene segments

2. MHC Molecules
There are two general classes of MHC molecules, and at least one or the other, or both, are found on the surface of all nucleated cells in the body.
Class I molecules (MHC-I) are built into almost all body cells and are used to present non-self proteins (from bacteria or viruses, for example) to cytotoxic T cells.
Class II molecules (MHC-II) are only found only on APCs.
Both classes are important for antigen processing and presentation.
Genetic recombination is the shuffling and rearranging of a few hundred versions of several small gene segments

3. MHC Molecules
When APCs come across foreign antigens, they are broken down and loaded onto MHC-II molecules of APCs.
The Class II MHC molecules on the APCs present the fragments to helper T cells, which stimulate an immune reaction from other cells.
Clones of activated T cells (and the antibodies from plasma cells) are now “competent” to recognize similar antigenic fragments displayed by infected cells throughout the body and respond harshly.

4. MHC Molecules Infected body cells present antigens using
22_14

5. MHC Molecules
Cytotoxic T cell destruction of an infected cell by release of perforins that cause cytolysis
Microbes are destroyed by granulysin.
22_14

6. Clonal Selection
Clonal selection is the process by which a lymphocyte proliferates and differentiates in response to a specific antigen.
A clone is a population of identical cells, all recognizing the same antigen as the original cell.
Lymphocytes undergo clonal selection to produce:
Effector cells (the active helper T cells, active cytotoxic T cells, and plasma cells) that die after the immune response.
Memory cells that do not participate in the initial immune response but are able to respond to a subsequent exposure - proliferating and differentiating into more effector and memory cells.
Memory cells have long life spans

7. Cytokines
Cytokines are chemical signals from one cell that influences another cell.
They are small protein hormones that control cell growth and differentiation:
Interferon
Interleukins
Erythropoietin
Tumor necrosis factor

9. Antibodies
Antibodies (also called immunoglobulins or Igs) are produced by plasma cells through antibody-mediated immunity.
Antibodies are composed of 4 peptide chains:
Two heavy chains and two light chains
Disulfide bonds link the chains together in a Y-shaped arrangement.
The variable region (antigen-binding region) gives an antibody its specificity.
The stem is similar for each class of antibody.

10. Antibodies
Single-Unit antibody structure
22_19

11. Antibodies Some of the ways antibodies are effective include:
Neutralizing a bacterial or viral antibody, or a toxin by covering the binding sites and causing agglutination and precipitation (making what was soluble, insoluble)
Activating the classical
complement pathway
Enhancing phagocytosis -
a process called
opsonization

12. Antibodies
The complement system is a series of blood proteins that often work in conjunction with antibodies – it can be activated by multiple pathways in a step-wise or cascading fashion. It encourages vasodilation and inflammation, antigen opsonization,
and antigen
destruction.
The main proteins
are C1-C9.