B-229. Cellular and Immunological Responses of Alveolar Macrophages to Mycobacterium immunogenum, a Species Associated with Occupational Hypersensitivity Pneumonitis
Non-tuberculous mycobacteria (NTM) have been associated with hypersensitivity pneumonitis (HP), which is an immune-mediated human lung disease. In particular, Mycobacterium immunogenum (MI), a relatively newly identified species of the M. chelonae-M. abscessus group of NTM, is considered as the etiological agent in occupational HP reported in machinists as a result of exposure to mycobacteria-contaminated metal working fluid (MWF) aerosols. Our laboratory has isolated several genotypes of M. immunogenum from HP-associated and other MWF operations. Macrophages play a central role in host defense in the exposed lung. Hence, understanding their response to MI exposure will help understand the HP pathogenesis mechanisms. In this study, murine alveolar macrophage cell line, MH-S was used to understand the interaction between MI and the exposed host lung. The MH-S cells were infected with varying doses (0.001, 0.01, 0.1, 1.0, 10. and 100 MOI) of the three individual MI genotypes (isolated from HP-associated MWF) for different time intervals and the macrophage response to infection was measured in terms of cytokine expression, nitric oxide (NO) induction, loss of cell viability and cytotoxicity. All MI genotypes markedly induced NO and cytotoxicity in the macrophage cells in a dose- and time- dependent manner. Macrophage viability decreased up to 68% at 24h of MI infection (10 MOI). Among the three genotypes, MJY-3 induced the most intense macrophage cellular response to in terms of NO production, cytotoxicity and cell viability. All three MI genotypes up-regulated the expression of pro-inflammatory cytokines and down-regulated the anti-inflammatory cytokine (IL-10) expression in dose- and time- dependent manner. Majority of the tested cytokines peaked at 24h and 10 MOI, except some that peaked at 12h of infection. Regardless of their origin, the three MI genotypes activated the alveolar macrophages and the overall macrophage response peaked at 10 MOI at 24h. This is the first report on the host macrophage response to M. immunogenum.