Lymph node.............? - jamebond

[ArchivalUser]

http://img259.imageshack.us/img259/4690/83338327.jpg
Thanks..........

[ArchivalUser]

germinal center, isotype switching

[ArchivalUser]

agree

-"Constant Region" of heavy chain rearrange (Isotype Switching)
-"Variable Region" undergo "Somatic Hypermutation"

[ArchivalUser]

Isotype switching..............

B-cell precursors proliferate and mature in the bone marrow. Mature B-cells leave the bone marrow and migrate to lymphoid organs where they are exposed to antigens. On first exposure to a new antigen, a clone of B-cells becomes activated.

Some activated B-cells differentiate into short-lived plasma cells that release antigen-specific IgM (primary response). The majority of activated B-cells migrate into the lymphoid follicles located in the cortical region of lymph nodes. The lymphoid follicle germinal center is the site of B-cell proliferation during the immune response. The arrow points to the germinal center of a lymphoid follicle.

In the germinal center, activated B-cells form memory cells that remain in the lymph node until the next encounter with the same antigen. Isotype switching (from IgM to other types of immunoglobulins) also occurs in the germinal centers late in the primary response. This gives activated B-cells the ability to produce antigen-specific antibodies of different types (e.g. lgG, IgA, IgE). Isotope switching is stimulated by T-cell cytokines like IL-2, IL-4, IL-5, IL-6, and INF-y. All subsequent encounters with the same antigen generate a response of predominantly lgG release.

Heavy chain differences distinguish the five isotypes: IgM, lgG, IgA, IgE, and lgD. Heavy chain constant regions are isotype specific, while their variable regions are antigen-specific. Light chains are also antigen-specific, and do not determine isotypes. In isotype switching, the genes responsible for the heavy chain constant regions are rearranged.