Mitogen-induced human IgG subclass expression.

To investigate human isotype expression among lymphocyte populations, we have studied IgG subclass production by splenocytes, tonsil cells, and peripheral blood lymphocytes (PBL) after stimulation with a panel of nine mitogens. Response magnitudes varied with tissues: all mitogens produced the strongest responses with splenocytes and the smallest with PBL. In addition, the IgG subclass maximally stimulated by a particular mitogen also depended on the tissue studied. For example, LPS mainly stimulated IgG2 in PBL and IgG1 in spleen. Interestingly, the response patterns seen in splenocytes suggest a large and coordinate expression of IgG1 and IgG3 subclasses. Implications of these findings are discussed with respect to immunoglobulin gene organization and human disease states.