Comparison of the plaque-stimulating and thymocyte-stimulating activities derived from human monocytes.

Human monocytes have been reported to release factors that can elicit distinct responses from a number of different target cells. In this report, it is shown that most of the thymocyte-stimulating activity in supernatants of endotoxin-stimulated monocytes can be separated from the plaque-stimulating factor (BAF) by gel filtration and isoelectric focusing; however, since these activities could not be entirely resolved, the question was addressed whether the plaque-stimulating activity of BAF depends upon the stimulation of T-cells. Several critical experiments are reported which fail to support this hypothesis. On the other hand, these experiments led to the observation that the response to BAF depends on both an IgM-positive B-cell and a G10-adherent, plastic nonadherent, IgM-negative, irradiation-insensitive cell found in nude splenocytes. Finally, the possibility is discussed that this factor may be responsible for many of the physiological sequelae of infection.