Immunoglobulin synthesis in a patient with C4 deficiency: functional immaturity of peripheral blood lymphocytes

Peripheral blood lymphocytes from a systemic lupus erythematosus patient with homozygous C4 deficiency were stimulated in vitro. Although T cell independent stimulation (Epstein-Barr virus) induced normal proportions of IgM secreting cells. IgG and IgA secreting cells were almost absent. Virtually no immunoglobulin secretion was obtained after T cell dependent stimulation (pokeweed mitogen). Cell fractionation experiments indicated that the low pokeweed mitogen response, at least with regard to IgG and IgA production, was mainly due to impaired B-lymphocyte function. The serum IgG subclass distribution pattern of specific antibodies against certain carbohydrate antigens demonstrated a relative lack of IgG2 antibodies. The findings were consistent with functional immaturity of B lymphocytes in the patient.