Thursday, May 31, 2012

Anatomy and Physiology: The Humoral and Cell Mediated Immune Responses

Humoral (Antibody-Mediated) Immune Response


When there is a first exposure to an antigen, these free antigens activates B cells.  The lymphocyte "switches on" and undergoes clonal selection, which is when the lymphocyte grow and multiplies rapidly to form many identical cells called clones.  This clone formation is the primary humoral response.  Most of the B cell clone members become plasma cells, which produce the same highly specific antibodies.  The plasma cells die off after 4-5 days and the antibody level in the blood goes down.  There are some B cell clone members that don't become plasma cells but instead, become memory cells that can respond to the same antigen later.  As a result, in later immune responses or secondary humoral responses, the response to the presence of the antigen is more faster, prolonged, and effective.


Cellular (Cell-Mediated) Immune Response


In the cellular immune response, T cells are sensitized by binding to an antigen and a self-protein on the macrophage surface.  After clonal selection, clone members differentiate into memory T cells and effector T cells.  There are several different classes of T cells: cytotoxic (killer) T cells, helper T cells, memory T cells, and suppressor T cells.


Cytotoxic (killer) T cells: directly attack and kill infected and cancerous cells


Helper T cells: binds with specific antigen presented by a macrophage; stimulates production of other immune cells (cytotoxic T cells and B cells); acts directly and indirectly by releasing lymphokines


Memory T cells: descendant of a T cell; forms during initial immune response (primary response); may exist in the body for years to allow it to respond more quickly to later infections by the same antigens


Suppressor T cells: slows or stops activity of B and T cells when the infection or attack has been conquered




Sources:
Elaine N. Marieb's Essentials of Human Anatomy and Physiology, Eighth Edition

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