CCL1-producing monocytes with immunosuppressive properties (M2bMonocytes) have been demonstrated in peripheral blood of severely burned patients. Also, these burned patients are shown to be carriers of CCL2-producing PMN (PMN-II). Neither M2bMonocytes or PMN-II has been demonstrated in peripheral blood of healthy donors. In this study, the role of PMN-II on the conversion of naive monocytes to M2bMonocytes was investigated. PMN-II were induced from immuature PMN after stimulation with 0.0075% SAC and 10-6 M terubutaline. Immature PMN were obtained from peripheral blood of healthy volunteers 3 hrs after 1-hr of programmed exercise, as previously described. PMN-II (upper chamber) were transwell-cultured with naive monocytes (syngeneic to PMN-II, lower chamber) for 24 hrs. Cells harvested from the lower chamber were re-cultured for 24 hrs for the production of CCL1 (a biomarker of M2bMonocytes), and culture fluids obtained were assayed for CCL1 by ELISA. Naive monocytes did not produce CCL1 even when they were transwell-cultured with healthy donor PMN (normal PMN). However, CCL1 was detected in culture fluids of naive monocytes that were previously cultured with PMN-II. Anti-CCL2 mAb inhibited the appearance of M2bMonocytes in transwell-cultures between naive monocytes and PMN-II. Also, M2bMonocytes were generated from naive monocytes after they were cultured with recombinant CCL2. These results indicate that PMN-II, or CCL2 produced by PMN-II, play an important role on the generation of M2bMonocytes commonly demonstrated in burn patient peripheral blood. This study was supported by SHC NA #8840.