Evaluation of immune associated cellular phenotypes in lesions of vervet monkeys (cercopithecus aethiops) experimentally infected with leishmania malor.

Abstract

Studies were conducted to evaluate immune associated cellular phenotypes in the lesion areas ofvervet monkeys (Cercopithecus aethiops) experimentally infected with Leishmania major. Different immune associated cell types recruited into the lesion sites as a result of primary, secondary infections were characterized using established cross reactive antihuman monoclonal antibodies in combination with the immunoperoxidase methods. Nine adult vervet monkeys were used in this study. The primary infection group consisted of 4 adult naive animals of either sex. The secondary infection group also consisted of 4 adult animals of either sex which had self cured from experimental L. major infection. One extra naive control animal was also included. Animals in both groups were inoculated with 5x107 stationary phase promastigotes of L. major and observed after every 2 weeks for lesion development. Samples from the skin and draining lymph node were obtained at six weeks post infection and used for staining. Studies from non infected areas taken as control'skin sections in all the animals revealed the presence of resident CD8 positive T cells both in the epidermis and dermal layers of the skin. These (CD8 positive T cells) were smooth in morphology with majority being in the dermal layer. B cells, CD 16 and CD4 positive cells were virtually absent in the normal skin while there was a negligible population of macrophages. These cells, including the keratinocytes only expressed MHC class 1 antigens. A heavy cellular infiltration consisting primarily of mononuclear cells was observed at the lesion sites in both primary and secondary infection groups. Majority of these cells expressed both MHC class 1 and 2 and the CD8+ phenotypes. The main cell type in the infiltration was CD8 positive T cell. CD 16 positive cells were also recruited into the lesions and these had a Lymph nodes draining the control skin sites recorded a lower population of cells than those draining lesions. Majority of these cells were both MHC class 1 and 2 positive. There continued to be a higher population of CD8 positive T cells than both B cells and CD4 positive T cells. The difference in CD 16 positive cells between nodes draining control sites and lesions was not clear. In general, cellular changes occurring in the skin were reflected in the draining lymph nodes in both infection groups. Nodes draining lesion sites were enlarged, a feature not observed in those draining control sites. There were positive delayed type hypersensitivity (DTH) reactions in animals with active infection and those that had self cured. This indicated that the experimental animals developed cell mediated immunity. The results show that the CD8+T cell phenotype is the main c.elltype restricting parasites to the lesion site in both primary and secondary L. major infection in vervet monkeys. The results .also show that cellular phenotypes expressing CD3, CD8, CD16 and MHC classes 1 and 2 antigens restricted parasites to the lesion site in both primary and secondary L. major infections in vervet monkeys.