Modulation of human mononuclear cell responses by neutrophil-derived factors

We previously reported that neutrophil (PMN)-derived factors modulated human mononuclear cell (MNC) responses. These interactions are important in understanding MNC localization, growth, and activation in inflammatory events such as occur in the rheumatoid synovium. We have partially identified and characterized a human neutrophil-derived, lymphocyte-enhancing factor (N-LEF). Highly purified PMN, devoid of MNC or platelets, were obtained by density gradient sedimentation. Supernatants (spt) were prepared from PMN phagocytosis of complement-coated zymosan particles. N-LEF was determined by [3H]TdR uptake or Ig secretion by stimulated MNC of cell lines. Neutral protease activity was quantitated by digestion of 125I-labeled Hb. Sodium dodecylsulfate (SDS) polyacrylamide gel electropheresis (PAGE) was carried out in 15% gels. We found (1) N-LEF biologic activity was cold stable, heat labile, nondialyzable, and diminished at acid pH (less than 4) or alkaline pH (greater than 10); (2) N-LEF biologic activity was abrogated by human plasma; (3) spt contained neutral protease and granule-associated but not cytoplasmic enzyme activities; (4) protease activities (for Hb, fibrin, ATEE, and Ac-Phe-BNa) were recovered from aprotinin-sepharose affinity columns and contained approximately 25,000 and approximately 28,000 molecular weight material on SDS-PAGE; (5) absorbtion of N-LEF spt on aprotinin-sepharose diminished both protease and biologic activities; and (6) N-LEF biologic activity and nonelastase neutral protease activity were found in approximately 13,000 mol wt fractions of Sephadex G100 (where cathepsin G chromatographs). Our observations suggest that phagocytosis of immune complexes by PMN induces release of a mononuclear cell enhancing factor, N-LEF, which may be an important mediator of inflammation, promoting transition from an acute to a chronic inflammatory response. Biologic properties of N-LEF are those of cathepsin G.