Subpopulations of T Lymphocytes in the Peripheral Blood, Dermal Lesions and Lymph Nodes of Post Kala-azar Dermal Leishmaniasis Patients

Distribution of different subpopulations of T cells in the dermal lesions, lymph nodes and peripheral blood of post kala-azar dermal leishmaniasis (PKADL) patients was studied by using appropriate phenotypic markers for CD2⁺, CD4⁺ and CD8⁺ cells. Histopathological studies of skin lesions showed marginal to massive infiltration of mononuclear cells depending upon the duration of illness and type of lesions. Thus, while the hypopigmented patches were represented by small focal collections of lymphocytes with scanty parasites in the dermis, these were replaced at the nodular stage with massive granulomas consisting of lymphocytes, plasma cells and histiocytes with numerous amastigotes. The involvement of CD4⁺ and CD8⁺ cell types in these lesions also showed a gradual change from the appearance of a few cells of both the phenotypes in early hypopigmented type to massive accumulation of cells, primarily of CD8⁺ phenotype, in the granuloma of nodular type. However, the observed preponderance of CD8⁺ cells at the lesion site of chronic PKADL patients is in contrast to their peripheral blood CD4⁺/CD8⁺ cell ratio (1.9:1) which remained within the normal limits. Similar studies of lymph nodes from PKADL patients with lymphadenopathy revealed infiltration of the cortical areas by T cells which were more of CD8⁺ than CD4⁺ phenotypes. All these results document the involvement of CD8⁺ cells in leishmanoid lesions. Thus, it is likely that these cells, in association with appropriate subpopulations of CD4⁺ cells, play a profound role in the evolution of dermal pathology in PKADL.