B Lymphocyte Stimulation and Suppression by the Fc Portion of Immunoglobulin
The Fc region of immunoglobulin (Ig), whether in the form of an Fc fragment1, aggregated Ig1,2 or an immune complex3 can induce normal murine splenic B cells and human peripheral blood B lymphocytes to proliferate and differentiate to polyclonal antibody-secreting cells. Only the Fc portion of Ig is able to induce this response. Fab or F(ab′)2 fragments, either soluble or heat aggregated, are inactive. Some change has to occur in the Fc part of the molecule since unaggregated intact IgG is inactive. It appears that the alterations of IgG that occur with heat aggregation and after interaction of IgG antibody with antigen, as well as by splitting Fc from the parent molecule by papain digestion, all expose a site in the Fc portion that is masked in the intact molecule and which is critical in mitogenesis. The mitogenic signal of Fc fragments does not appear to depend on approximation of Fc regions by aggregation. Mitogenically active human Fc fragments obtained by cleavage with papain have a sedimentation rate of Fc monomers and do not appear to aggregate in the culture medium1. Further, heat aggregation or chemical crosslinking of purified Fc fragments does not increase their mitogenicity (unpublished observation).
KeywordsSpleen Cell Mitogenic Signal Lymphocyte Stimulation Spleen Cell Culture Papain Digestion
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