Immunoglobulin synthesis after HLA-identical marrow grafting. V. The role of peripheral blood monocytes in the regulation of in vitro immunoglobulin secretion stimulated by pokeweed mitogen.

The ability of purified monocytes to regulate in vitro immunoglobulin (Ig) production was examined in 12 patients after HLA-identical marrow grafting. Five patients were studied less than 3 mo after grafting and seven more than 1 yr after grafting. One of the former had acute graft-vs-host disease and five of the latter had chronic graft-vs-host disease. Ficoll-Hypaque-separated peripheral blood mononuclear cells from patients, normal marrow donors, or healthy unrelated individuals were separated into T and non-T cells by sheep erythrocyte rosetting. Highly enriched monocyte and B cell subpopulations were obtained by placing the non-T cells over discontinuous Percoll gradients. Co-cultures of patient or normal monocyte populations with either normal or patient T and B cells with pokeweed mitogen were performed. A hemolytic plaque assay was used to assess Ig secretion after 6 days of culture. Co-culture of T and non-T cells from 10 of 12 patients failed to produce Ig. Monocyte-enriched fractions from all patients provided normal accessory cell functions when co-cultured with normal T and B cells. Two of five patients with chronic graft-vs-host disease had monocytes that suppressed Ig synthesis at high ratios of monocytes to normal T and B cells. Normal monocyte-enriched fractions did not restore Ig production to T and B cells of patients whose T and non-T cells failed to produce Ig. These data indicate that the observed defects in pokeweed mitogen-driven Ig secretion after marrow grafting are due primarily to defective T and B cell functions and that the monocyte accessory function is intact in most patients studied.