Role of T Lymphocytes in the Humoral Immune Response

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Abstract
The humoral response to dinitrophenyl-keyhole limpet hemocyanin (DNP-KLH) was measured in thymectomized, irradiated, bone marrow-reconstituted, and rabbit antimouse thymocyte antiserum-(ALS)treated (Tx-BM) mice. The total anti-DNP antibody response, as measured by plaque-forming cells, was not severely decreased, but was changed in character from the normal predominantly IgG secondary response to a persistently IgM response. The IgG secondary response was partially restored to Tx-BM mice by injecting syngeneic thymocytes i.v. as late as 1 week before or activated thymus-derived (T) lymphocytes on the day of secondary antigen administration, implying that significant changes occur in the precursor population in the absence of T cells. This was supported by the finding that antigen-binding cells (ABC), the presumed precursors of antibody-secreting cells, proliferated normally in Tx-BM mice. However, instead of the replacement of µ-bearing ABC by significant numbers of ABC bearing other classes of immunoglobulin, as seen in the normal response to antigen, the ABC in Tx-BM animals possessed µ-receptors throughout the immune response. It is suggested that the generation or activation of non-µ-bearing ABC is strikingly impaired in the absence of a normal complement of T cells and may be responsible for the decreased IgG antibody production.

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