Modulation of monocytic cell activity and virus susceptibility during differentiation into macrophages

A major component of innate immune responses relies on monocytes and macrop hages, virus infection of which will pose a particular problem for immunolo gical defense. Consequently, the monocytic cell differentiation pathway was analyzed in terms of cellular modulations therein and their relation to mo nocytotropic virus infection. Differentiation was characterized by downregu lation of CD14, MHC Ags, the monocytic SWC1 marker, and p53; concomitant up -regulation of the SWC9 macrophage marker, a putative porcine CD80 (detecte d with anti-human CD80 Ab), and acid phosphatase secretion were also charac teristic. Elevated phagocytic and endocytic activities as well as endosomal /lysosomal acidification were identified as being important to the macropha ge, In contrast, monocytes possessed high accessory activity, This was mult ifactorial, concomitantly requiring 1) high MHC Ag expression; 2) enzyme ac tivity of esterase, peroxidase, myeloperoxidase, and. 5' nucleotidase in pr eference to glucosidase, galactosidase, and glucuronidase; and 3) elevated capacity for spontaneous IL-1 production, Only with all parameters was effi cient stimulation of Ag-specific lymphocytes possible. These results point to a continuous process during differentiation, involving inter-related cha racteristics linking the more accessory monocyte to the scavenger macrophag e, both in vitro and in vivo. Of particular interest was how these characte ristics related to monocytotropic virus infection, and how a particular vir us could show a clear preference for the differentiating macrophages, Such results not only further our understanding of porcine immunology, but also provide evidence and a potential model for the determination and characteri zation of monocytotropic virus-host cell interactions.