Differential infection of porcine alveolar macrophage subpopulations by nonopsonized Mycobacterium bovis involves CD14 receptors

The resurgence in mycobacterial infection worldwide has led to renewed attention to the pathogenesis of Mycobacterium species. The purpose of this study was to characterize the infection of alveolar macrophages (AMs) by nonopsonized Mycobacterium bovis, and to elucidate the mechanism by which a differential infection of subpopulations of AM may occur. A difference in susceptibility to Mycobacterium bovis infection of subpopulations of AMs was observed, such that the least dense cells were the least susceptible (21.4 ± 10.7%) and the most dense cells were the most readily infected (61.8 ± 5.6%). The percentage of AMs staining for CD14 receptors showed a similar differential distribution, with fewer of the least dense cells expressing CD14 and a greater percentage of the most dense cells staining for CD14 receptor expression. To investigate the role of CD14 receptors in the infection of AMs, anti-CD14 antibody was added to the cell cultures, Infection of AM by Mycobacterium bovis was blocked by up to 60.2% by anti-CD14 antibody but not by isotype control antibody. The results of this study suggest that Mycobacterium bovis selectively infects AM subpopulations, specifically those with the greatest expression of CD14, a putative receptor mechanism for Mycobacterium bovis infection of porcine AM.