The effect of isoprinosine on the PHA response of monocyte-depleted and undepleted peripheral blood mononuclear cells.

Isoprinosine has been reported to stimulate immunological responses involving different cell types. This study attempted to identify which cell type responds to isoprinosine in the blast transformation assay using the mitogen phytohemagglutinin (PHA). Human peripheral blood mononuclear cells, and the same cell population depleted of monocytes, were used to determine whether the absence of monocytes alters the response to isoprinosine. To determine whether there is a critical period of time during the assay when isoprinosine has its effect, the cells were selectively preexposed to drug and/or mitogen for a limited period of time, then cultured. Depletion of monocytes in itself augmented the response to mitogen, but the response could still be potentiated by isoprinosine, indicating that the drug's effect was on cells other than monocytes. Preexposure to isoprinosine and/or PHA, followed by culture with PHA with or without isoprinosine, showed that PHA initiates transformation within the first 3 hours and that initiation, a monocyte function, is not sensitive to isoprinosine. Both approaches suggest that isoprinosine does not affect monocytes and that it probably acts on T cells to produce its stimulatory effect in this in vitro assay.