Selective IgM deficiency: functional assessment of peripheral blood lymphocytes in vitro.

The functional aspects of the peripheral blood lymphocytes from 6 patients with primary selective IgM deficiency (sIgMD) were analyzed to elucidate its pathogenesis. The surface IgM positive B cells were present at almost the same percentage as in controls, but the percentage of cluster of differentiation (CD)4+ T cells was higher and that of CD8+ T cells was low. The patient B cells showed a significantly lower proliferative response to Staphylococcus aureus Cowan strain I (SAC) than control B cells and did not produce a significant amount of IgM when co-cultured with control T cells. Interestingly, mitomycin C (MMC)-treated patient T cells induced a greater amount of IgM production by control B cells. In addition, patient B cells treated with SAC and B cell differentiation factors (BCDF) failed to secrete IgM. These results suggest that the pathogenesis of sIgMD may be mainly due to an intrinsic defect in B cell maturation.