Immunomodulatory properties of platelet factor 4: prevention of concanavalin A suppressor-induction in vitro and augmentation of an antigen-specific delayed-type hypersensitivity response in vivo.

The immunomodulatory properties of platelet factor 4 (PF4) have been examined in vitro and in vivo. This agent prevented the induction of concanavalin A (Con A)-induced suppressor cells in vitro in a dose-dependent manner but it did not affect the function of established Con A suppressor cells. This effect was not due to an enhanced production of interleukin-2 (IL-2) by lymphocytes exposed to PF4. The delayed-type hypersensitivity (DTH) reaction to sheep erythrocytes (SRBC) was used as a model for the generation of antigen-specific suppression in vivo. PF4 enhanced the magnitude of the swelling following SRBC challenge 10 days after sensitization by the i.p. route or following sensitization by both the s.c. and i.p. routes. These studies show that PF4 has immunomodulatory activities in well-defined models of cell-mediated immunity and suggest that this agent has a potential use in the dissection of events in antigen-specific suppression.