The antigen-specific responses among individuals infected with L. braziliensis also

revealed a significant expansion of T cells expressing Vβ12 (Fig. 3). Interestingly, this was the same subpopulation identified by Clarencio et al. in CL caused by L. braziliensis and stimulated by SLA of L. amazonensis[29]. This finding may suggest an existence of common dominant response between different species of Leishmania leading to the expansion of a similar subpopulation of T cells. Frequency differences are only one possible measure of check details the involvement of a specific subpopulation of T cells in an active immune response. It is possible that slight changes or no global change in the frequency of T cell subpopulations will be noted due to a balance between expansion and death of responding T cells. However, by determining the portion of a given subpopulation committed to an activated phenotype, memory phenotype or producing specific cytokines, we can determine

their relative involvement and possible functional role in a protective or pathogenic immune response. Thus, we performed comparative analyses between the different Vβ subpopulations of the proportion of cells expressing either a marker of late T cell activation, the class II molecule, HLA-DR, or a marker associated with many memory T cells, CD45RO. These markers were measured without in vitro antigenic restimulation with the goal of determining their involvement in the host actively infected with Leishmania. Strikingly, CD4+ T cells expressing Vβ BI2536 regions 5·2, 11 and 24 displayed a significantly higher portion of cells expressing CD45RO and HLA-DR (Fig. 4). Thus, these subpopulations demonstrated a phenotype consistent with greater involvement in an ongoing immune response

than the Megestrol Acetate other T cell subpopulations. Importantly, two of these subpopulations (Vβ5·2 and Vβ11 CD4+ T cells) also displayed an expansion after antigen specific stimulation in vitro (Fig. 3). In order to understand more clearly the functional potential of specific subpopulations of CD4+ T cells based on Vβ expression, we went on to measure their relative commitment to production of antigen-specific proinflammatory (IFN-γ and TNF-α) and anti-inflammatory (IL-10) cytokines. Strikingly, the same three Vβ-expressing subpopulations arose as having a disproportionately high percentage of the SLA-stimulated T cells committed to cytokine production compared to the majority of the other Vβ-expressing T cell populations (Fig. 5). Thus, CD4+ T cell subpopulations defined by Vβ 5·2, 11 and 24 in CL patients displayed higher production of IFN-γ, TNF-α and IL-10 compared to several other subpopulations of T cells in CL patients. An important aspect of human leishmaniasis and other infectious diseases is the balance of inflammatory and down-regulatory cytokines.