Microfilariae of Brugia malayi contain a T cell mitogen

We investigated the mechanisms that lead to polyclonal hypergammaglobulinemia in persons exposed to or infected with lymph-dwelling filarial parasites. Extracts of microfilariae of Brugia malayi induce the in vitro proliferation of lymphocytes from nonsensitized donors. The mitogenic factor(s) responsible for this effect is of low molecular weight (Mr) and acts on T4+ cells but not on T8+ T lymphocytes or on B cells. T4+ lymphocytes stimulated with filarial mitogen augment the in vitro production of immunoglobulins by autologous B lymphocytes.