Modulation of human lymphocyte mitogen responsiveness and interleukin-2 production by polymorphonuclear leukocytes

The response of human peripheral blood lymphocytes to the mitogenic lectins phytohemagglutinin (PHA) and pokeweed mitogen (PWM) was examined in the presence of autologous polymorphonuclear leukocytes (PMN). Experiments were performed at sub-optimal and optimal mitogen concentrations employing lymphocyte: PMN ratios over a three log cell concentration range. Increases of up to 25,000-fold in mitogen stimulated lymphocyte proliferation as determined by 3H-thymidine incorporation were observed in PMN supplemented lymphocyte cultures as compared to lymphocytes cultured in the absence of PMN or with irradiated lymphocytes serving as filler cells. Similar results were obtained for PHA stimulated IL-2 production. The degree of enhancement of lymphocyte reactivity by PMN was also shown to be dependent on the source of serum supplementation (autologous versus xenogeneic). These results indicate that cell ratio is a critical factor in examining lymphocyte-PMN interactions as well as serum supplementation used. Early reports which have indicated a suppressive or no effect of PMN on lymphocyte reactivity based on a single lymphocyte: PMN cell ratio may need to be re-evaluated.