Role of complement receptors in uptake of Mycobacterium avium by macrophages in vivo: evidence from studies using CD18-deficient mice

Mycobacterium avium is an intracellular pathogen that has been shown to inv ade macrophages by using complement receptors in vitro, but mycobacteria re leased from one cell can enter a second macrophage by using receptors diffe rent from complement receptors. Infection of CD18 (beta(2) integrin) knocko ut mice and the C57 BL/6 control mice led to comparable levels of tissue in fection at 1 day, 2 days, 1 week and 3 weeks following administration of ba cteria. A histopathological study revealed similar granulomatous lesions in the two mouse strains, with comparable numbers of organisms. In addition, transmission electron microscopy of spleen tissues from both strains of mic e showed bacteria inside macrophages. Our in vivo findings support the hypo thesis that M. avium in the host is likely to use receptors other than CR3 and CR4 receptors to enter macrophages with increased efficiency.