Phenotypic characterisation of the monocyte subpopulations in healthy adult pigs and Salmonella-infected piglets by seven-colour flow cytometry

The present study describes the distinct bone marrow (BM) and peripheral blood (PB) monocyte subpopulations detected by seven-colour flow cytometry. Mononuclear phagocytes were identified as viable CD172a+ SWC8− CD203a− mononuclear leukocytes. After that, monocyte subpopulations were differentiated by using CD14, CD163 and SLA-DR markers. Four distinct monocyte subpopulations were found in the BM and PB. Based on the discovered populations two possible maturation pathways have been proposed. The first pathway was characterised by release of CD14hi CD163− SLA-DR− BM monocytes into the PB where they matured into CD14low CD163+ SLA-DR+ monocytes. In the alternative pathway the monocytes finalised their phenotypical maturation in the BM and then they were released into the PB as CD14low CD163+ SLA-DR+ cells. In Salmonella-infected piglets, the population of CD14low CD163+ SLA-DR+ monocytes was elevated in the BM and mesenteric lymph nodes (MLN), suggesting the role of this population in pathogenesis of Salmonella infection in pigs.