Flow cytometric determination of cellular sources and frequencies of key cytokine-producing lymphocytes directed against recombinant LACK and solubleleishmania antigen in human cutaneous leishmaniasis

Leishmaniasis, caused by infection with the protozoan parasite Leishmania, affects millions of individuals worldwide, causing serious morbidity and mo rtality, This study directly determined the frequency of cells producing ke y immunoregulatory cytokines in response to the recombinant antigen Leishma nia homolog of receptors for activated kinase C (LACK) and soluble leishman ia antigen (SLA), and it determined relative contributions of these antigen s to the overall cytokine profile in individuals infected for the first tim e with Leishmania braziliensis. All individuals presented with the cutaneou s clinical form of leishmaniasis and were analyzed for proliferative respon ses to LACK antigen and SW, frequency of lymphocyte subpopulations (analyze d ex vivo), and antigen-induced (LACK and SLA) cytokine production at the s ingle-cell level (determined by flow cytometry). The following were determi ned. (i) The Th1-type response previously seen in patients with cutaneous l eishmaniasis is due to gamma interferon (IFN-gamma) production by several d ifferent sources, listed in order of contribution: CD4+ T lymphocytes, CD4( -), CD8(-) lymphocytes, and CD8(+) T lymphocytes. (ii) SLA induced a higher frequency of lymphocytes producing IFN-gamma and tumor necrosis factor alp ha (TNF-alpha) than did LACK. (iii) LACK induced an activation of monocyte populations as reflected by an increased percentage of CD14-positive cells. (iv) Neither SLA nor LACK induced detectable frequencies of cells producin g interleukin-4 (IL-4) or IL-5. These data demonstrated a multifaceted immu ne response to SLA in human Leishmaniasis involving Th1 CD4(+) T lymphocyte s (IFN-gamma (+) and IL-10(-)/IL-4(-)), Tcl CD8(+) T cells (IFN-gamma (+), and IL-10(-)/IL-4(-)), and a high frequency of TNF-alpha -producing lymphoc ytes. Moreover, it was determined that the recombinant antigen LACK acts as a weak inducer of Th1-type lymphocyte responses compared to SLA.