Analysis of the effect of mast cell granules on lymphocyte blastogenesis in the absence and presence of mitogens: identification of heparin as a granule-associated suppressor factor.

To explore the effect of mast cell products on lymphocytes, the blastogenic response of lymphocytes to mast cell granules in the absence and presence of mitogens was determined. Membrane-free granules (MFG) and dialyzed, washed histamine-free granules (DWG) in the absence of mitogens did not induce significant blastogenesis in peripheral blood mononuclear cells (PBMC) before or after partial depletion of macrophages (5 to 10%). In contrast, concanavalin A- (Con A) (5 micrograms/ml), pokeweed mitogen- (PWM) (1/200 dilution), tetanus toxoid-, and Candida-, but not phytohemagglutinin-, induced blastogenesis in macrophage-depleted PBMC were inhibited by both MFG and DWG. Fractionation of solubilized DWG by anion exchange Dowex chromatography into protein- and heparin-rich fractions revealed the inhibitory activity resided in the heparin-containing fractions. The ability of commercial porcine heparin glycosaminoglycan as well as native rat heparin proteoglycan to inhibit lectin-induced blastogenesis in a dose-response fashion confirmed the previous data with the use of fractionated DWG. Histamine and commercial porcine heparin glycosaminoglycan were not additive in inhibiting lectin-induced lymphocyte blastogenesis. The inhibitory effect of heparin on Con A-induced blastogenesis could be overcome by adding excess Con A to macrophage-depleted mononuclear cell preparations and could be reproduced by using over-sulfated chondroitin 6-sulfate. This is the first examination of the ability of mast cell granules to influence lymphocyte function and the first demonstration of the ability of native heparin proteoglycan to modulate lymphocyte blastogenesis.