| Abstract: | Human macrophages (M phi) from most donors respond to inoculation with Mycobacterium avium serovar 4 (M. avium) by tumor necrosis factor alpha (TNF-alpha) production, which is of critical importance for proper defense against microorganisms. An initial infection of M phi with M. avium results in an incapacity to accumulate TNF-alpha mRNA after reinfection with M. avium, indicating adaptation to a hyporesponsive state by preexposure of the cells to M. avium. Adaptation to stimulation with M. avium is abrogated by the cyclooxygenase inhibitor indomethacin. In the presence of prostaglandin E2, indomethacin-exposed, M. avium-treated M phi remain unresponsive to a subsequent M. avium stimulus to increase steady-state TNF-alpha mRNA, suggesting that prostaglandin E2 is instrumental for the adaptation to an M. avium challenge. TNF-alpha mRNA accumulation induced by a second M. avium stimulus in the presence of indomethacin is blocked by the protein tyrosine kinase inhibitor herbimycin. In contrast, the initial M phi response to M. avium is inhibited by staurosporin, an inhibitor of phospholipid Ca(2+)-dependent protein kinases, indicating that the initial and the successive TNF-alpha responses to M. avium are dependent on different mechanisms. |
