Cellular phenotypes in Trypanosoma congolense infected sheep: the local skin reaction

Mononuclear cell subpopulations in local skin reactions (chancres) in sheep infected with metacyclic forms of Trypanosoma congolense were studied by indirect immunoperoxidase staining using a panel of monoclonal antibodies (MoAbs) specific for ovine leucocyte subsets. Morphometric analysis revealed significant increases in numbers of cells expressing CD5, CD4, CD8, CD45R (mainly B cells), major histocompatibility complex (MHC) class II antigens, Fc receptors (FcR) on macrophages (VPM32) and FcR on B cells and macrophages (VPM33) from five days post-infection. B cells which also expressed MHC class II were found mainly in dense aggregates. The CD4/CD8 ratios were raised over pre-infection levels at 5-7 days post-infection. In sheep which had been infected, treated with trypanocidal drugs and then challenged with an heterologous serodeme of T. congolense, changes in cellular phenotype kinetics were similar to those seen in the skin in primary infections. Sheep superinfected with either an homologous or an heterologous, T. congolense serodeme showed only mild cellular infiltration and slight increases in various cellular phenotypes at the sites of inoculation.