Release of a suppressor cell-inducing factor by monocytes from patients with pulmonary tuberculosis

We observed that blood monocytes from tuberculous patients secreted a factor which induced suppressor cells. Monocyte-enriched adherent cells were prepared from peripheral blood mononuclear cells (PBMC) of 14 patients with active pulmonary tuberculosis or nine healthy tuberculin skin reactors and were cultured without any stimulus for 5 days. For induction of suppressor cells, PBMC from a healthy tuberculin reactor were cultured with the monocyte culture supernatants (MN SUP). After 2 days, those cells were washed and irradiated, then tested for their ability to suppress blastogenesis in autologous PBMC stimulated with purified protein derivative (PPD). Mean activity of suppressor cell induction in MN SUP of patients with pulmonary tuberculosis was significantly greater than that of healthy controls. In contrast, PPD-induced blastogenic responses in PBMC from tuberculous patients were lower than in controls. When we divided those tuberculous patients into high and low secretor groups on the basis of the magnitude of suppressor cell induction by MN SUP, PBMC from the high secretors had lower direct blastogenic responses to PPD than those of the low secretors. The blastogenic responses of PBMC from the high secretors, but not the low secretors, were significantly lower than those of healthy subjects. MN SUP which contained high suppressor cell-inducing activity had no effect on PPD-induced blastogenesis of PBMC from a healthy donor. These data suggest that monocytes from some tuberculous patients indirectly depress lymphocyte blastogenesis through a suppressor cell-inducing factor.