The Dual Nature of the Specific Immune Response
Stage I. Lymphocytes originate in hemopoietic tissue but go on to diverge into two distinct types: B cells, which produce antibody, and T cells, which produce lymphokines that initiate and coordinate the entire immune response.

Stage II. Macrophages detect invading foreign antigens and present them to lymphocytes, which recognize the antigen and initiate the specific immune response.

Stage III. Lymphocytes proliferate, producing clones of progeny which include groups of responder cells and memory cells.

Stage IV. Activated B lymphocytes become plasma cells which produce and secrete large quantities of antibody.

Stage V. Activated T lymphocytes differentiate into one of four subtypes, which regulate and participate directly in the specific immune response.

Essential Preliminary Concepts for Understanding Immune Reactions of Sections I-V
The surfaces of all cell membranes contain identity markers known as protein receptors. These cell markers function in identification, communication, and cell development. They are also self-identity markers.

Human cell markers are genetically determined by MHCs. MHC I codes for identity markers on all host cells. MHC II codes for immune receptors on macrophages and B cells. MHC III codes for secretion of complement C2 and C4.

The clonal selection theory explains that the immune system does not ordinarily attack its own host because all self-reacting lymphocyte clones are destroyed during fetal development.

During prenatal development, both B and T cells develop millions of genetically different clones through independent segregation, random reassortment and mutation. Together these clones possess enough genetic variability to respond to many millions of different antigens. Each clone, however, can respond to only one specific antigen.

The Lymphocyte Response System in Depth
Immature lymphocytes released from hemopoietic tissue migrate to one of two sites for further development. B cells mature in the stromal cells of the bone marrow. T cells mature in the thymus.

Antigens or immunogens are proteins or other complex molecules of high molecular weight which trigger the immune response in the host

Lymphocytes respond to a specific portion of an antigen called the antigenic determinant. A given microorganism has many such determinants, all of which stimulate individual specific immune responses.

Haptens are molecules which are too small to trigger an immune response alone, but which can be immunogenic when they attach to a larger substance, such as host serum protein.

Autoantigens and allergens are types of antigens which cause damage to host tissue as a consequence of the immune response.

Macrophages or other antigen processing cells (APC) bind foreign antigen to their cell surfaces for presentation to lymphocytes. Physical contact between the APC, T cells, and B cells activates these lymphocytes to proceed with their respective immune responses.

B cells produce five classes of antibody: IgM, IgG, IgA, IgD, and IgE. IgM and IgG predominate in plasma. IgA predominates in the body secretions. IgD binds to B cells as an antigen receptor. IgE binds to tissue cells, promoting inflammation.

Antibodies bind physically to the specific antigen that stimulates their production, thereby immobilizing the antigen and enabling it to be destroyed by other components of the immune system.

The anamnestic response means that the second exposure to antigen calls forth a much faster and more vigorous response that the first.

Monoclonal, or pure, antibodies can be produced commercially by fusing a plasma cell with a myeloma cell to produce an immortal hybridoma.

T cells do not produce antibodies. Instead they produce different lymphokines which play diverse roles in the immune response. Each subset of T cell produces a particular lymphokine that stimulates lymphocytes or destroys foreign cells.

Active immunity means that your body produces antibodies to some disease agent. If you contract the disease, you can develop natural active immunity. If you are vaccinated, your body will produce artificial active immunity.