LIPOARABINOMANNAN INDUCED CYTOTOXIC EFFECTS IN HUMAN MONONUCLEAR-CELLS

Mycobacteria produce large quantities of lipoarabinomannan, a cell wal l associated glycolipid, which confers virulence in many of the diseas e causing members of the genus. We studied the lipoarabinomannan induc ed altered signaling mechanism in human peripheral mononuclear cells. Lipoarabinomannan isolated from Mycobacterium smegmatis (a non-pathoge nic species) at concentrations of 2, 5 and 10 mu g ml(-1) was used for the study. It was found that protein kinase C activity of human monon uclear cells was significantly inhibited by lipoarabinomannan at these concentrations in a dose dependent manner. Calcium, phosphatidyl seri ne and diglyceride dependent phosphorylation of endogenous proteins (m ainly 90-, 80-, 66-, 38-, 36- and 34-kDa proteins) were also inhibited . Potentially cytotoxic superoxide anions generated by peripheral bloo d mononuclear cells were scavenged by lipoarabinomannan. It was also o bserved that incubation of peripheral blood mononuclear cells with lip oarabinomannan at concentrations of 5 and 10 mu g ml(-1) for 6 h direc ted the cells towards apoptotic cell death, confirmed by DNA degradati on analysis, microscopic observation of Wright-Giemsa as well as DAPI stained nuclei. These results clearly demonstrate that lipoarabinomann an from M. smegmatis may exert its cytotoxic activity via inhibition o f protein kinase C, a key signaling molecule inside the mononuclear ce lls, which ultimately affects the phosphorylation of various proteins imperative for cellular defence and survival. (C) 1998 Federation of E uropean Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.