Identification of a chemotactic, MCP-1-like protein from Mycobacterium avium

In the immunocompetent host, Mycobacterium avium is responsible for chronic localized pulmonary disease, which is characterized by the presence of increased numbers of activated T cells and macrophages in the lungs. M. avium organisms as well as sonic extracts of M. avium were found to act as chemoattractants for THP-1 cells as well as monocytes, monocyte-derived macrophages and alveolar macrophages obtained from normal human donors in an in vitro chemotaxis assay, where a significantly higher number of cells were found in wells containing M. avium compared to control wells. Proteolytic treatment of M. avium sonicate resulted in significant loss (50%) of chemotactic activity. Monoclonal antibodies against recombinant human monocyte chemoattractant protein-1 (MCP-1) were found to cross-react with a 34-kDa protein of M. avium sonicate on Western blot and inhibit M. avium sonicate-mediated chemotaxis of THP-1 cells (47%). These data suggest the presence of an 'MCP-1 like' molecule on M. avium. Recruitment of host immune regulatory cells to the site of infection by pathogens may be involved in generating a local immune response or may be a bacterial strategy for survival within the host by recruiting the cells that they infect, i.e. macrophages.