Interaction of Mycobacterium avium complex with human respiratory epithelial cells.

Adherence of Mycobacterium avium complex (MAC) to human respiratory epithelial cells (HEp-2) induced 2 distinct modes of internalization. In the first, MAC induced ruffling of HEp-2 cell membrane and formation of surface projections securing the bacilli on the surface, and concurrent membrane depressions, beneath the sites of attachment of bacilli, resulted in internalization of the organisms. The second mode involved formation of membrane folds wrapping around the bacilli, followed by internalization. Two MAC proteins of approximately 31 kD and approximately 25 kD, respectively, were identified that mediated these interactions specific for HEp-2 cells. The N-terminal amino acid sequence of the 31-kD MAC protein displayed homology with the 21-kD hypothetical protein of Mycobacterium tuberculosis, and the 25-kD MAC protein showed homology with Mn-superoxide dismutase of MAC and Mycobacterium leprae. These 2 HEp-2 cell-specific MAC proteins may be involved in the interaction of MAC with epithelial cells.