Trypanosoma cruzi: Killing and enhanced uptake by resident peritoneal macrophages treated with alpha-2-macroglobulin

We report that alpha-2-macroglobulin (A2M), the physiologically important plasma protease inhibitor and suspected immunomodulator, alters the functional ability of murine resident peritoneal macrophages (RM) to ingest and kill the infective trypomastigote stage ofTrypanosoma cruzi, the aetiological agent of Chagas' disease. Treatment of RM with 500 g/ml A2M for 30 min enhanced the uptake of trypomastigotes, epimastigotes, and amastigotes by 125%, 46%, and 300%, respectively. The same treatment also increased the phagocytosis of sheep erythrocytes opsonized with complement and IgG as well as of galactosylated asialoerythrocytes. After 60–90 min parasite-cell interaction, epi-and amastigotes were killed by the RM, whereas the infection with trypomastigotes was controlled only after 24 h. Other protease inhibitors, bovine serum albumin, and LPS showed no such effect. The production of hydrogen peroxide was not affected by A2M treatment, but the ultrastructural aspects showed trypomastigote damage and enhancement of macrophage membrane ruffling, indicative of macrophage activation. These results suggest that A2M has the ability to modulate, at least functionally, certain receptor-mediated endocytic pathways that, in concert with an activation of possibly oxygen-independent microbicidal mechanisms, could contribute to resistance against the parasite.Abbreviations A2M alpha-2-macroglobulin - F-A2M fast A2M - S-A2M slow A2M - RM resident macrophages - BT bloodstream trypomastigotes - EPI epimastigotes - AMA amastigotes - DMEM Dulbecco's Modified Eagle Medium - PBS phosphate-buffered saline - BSA bovine serum albumin - LPS bacto lipopolysaccharide - STI sovoean trypsin inhibitor - PPA pepstatin A - LPT leupeptin - PNT 1, 10-phenanthroline - TLCK N--tosy-L-lysine-chloromethylketone - E sheep erythrocyte - aE asialoerythrocyte - Gal R receptors for galactosylated particles