![](/olcweb/styles/shared/spacer.gif) | ![](/sites/dl/free/0072320427/title/cover_image.JPG) Foundations in Microbiology, 4/e Kathleen Park Talaro,
Pasadena City College Arthur Talaro
The Acquisition of Specific Immunity and Its Applications
Chapter Overview- The most specific host defenses are derived from a dual system of lymphocytes that are genetically programmed to react with foreign substances (antigens) found in microbes and other organisms.
- These cells carry glycoprotein receptors that dictate their specificity and reactivity.
- B lymphocytes have antibody receptors, T lymphocytes have T-cell receptors, and macrophages have histocompatibility receptors such as MHC and HLA.
- B cells and T cells arise in the bone marrow, where they proliferate and develop extreme variations in the expression of receptor genes.
- Differentiation of lymphocytes creates billions of genetically different clones that each have a unique specificity for antigen.
- The B cells reach final maturity in special bone marrow sites, and the T cells reach final maturity in the thymus gland.
- Both types of lymphocytes home (migrate) to separate sites in lymphoid tissue where they serve as a constant source of immune cells primed to respond to their correct antigen.
- Antigens are foreign cells, viruses, and molecules that meet a required size and complexity. They are capable of triggering immune reactions by lymphocytes.
- The B and T cells react with antigens through a complex series of cooperative events that involve the processing of antigens by macrophages and the assistance of helper T cells and cytokine stimulants (interleukins).
- B cells activated by antigen enter the cell cycle and mitosis, giving rise to plasma cells that secrete antibodies (humoral immunity) and long-lived memory cells.
- Antibodies have binding sites that affix tightly to an antigen and hold it in place for agglutination, opsonization, complement fixation, and neutralization.
- The amount of antibodies increases during the initial contact with antigen and rises rapidly during subsequent exposures due to memory cells ready for immediate reactions.
- T cells have various receptors that signal their ability to respond as helper cells, suppressor cells, and cytotoxic cells that kill complex pathogens and cancer cells.
- Acquired immunities fall into the categories of natural, artificial, active, and passive.
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