Human CD8+ T Cells Release Extracellular Traps Co-Localized With Cytotoxic Vesicles That Are Associated With Lesion Progression and Severity in Human Leishmaniasis.

Cell death plays a fundamental role in mounting protective and pathogenic immunity. Etosis is a cell death mechanism defined by the release of extracellular traps (ETs), which can foster inflammation and exert microbicidal activity. While etosis is often associated with innate cells, recent studies showed that B cells and CD4+ T cells can release ETs. Here we investigate whether CD8+ T cells can also release ETs, which might be related to cytotoxicity and tissue pathology. To these ends, we first employed an in vitro system stimulating human CD8+ T cells isolated from healthy volunteers with anti-CD3/anti-CD28. Using time-frame video, confocal and electron microscopy, we demonstrate that human CD8+ T cells release ETs upon stimulation (herein LETs - lymphocyte extracellular traps), which display unique morphology and functional characteristics. CD8+ T cell-derived LETs form long strands that co-localize with CD107a, a marker of vesicles containing cytotoxic granules. In addition, these structures connect the LET-releasing cell to other neighboring cells, often resulting in cell death. After demonstrating the release of LETs by human CD8+ T cells in vitro, we went on to study the occurrence of CD8-derived LETs in a human disease setting. Thus, we evaluated the occurrence of CD8-derived LETs in lesions from patients with human tegumentary leishmaniasis, where CD8+ T cells play a key role in mediating pathology. In addition, we evaluated the association of these structures with the intensity of the inflammatory infiltrate in early and late cutaneous, as well as in mucosal leishmaniasis lesions. We demonstrated that progression and severity of debilitating and mutilating forms of human tegumentary leishmaniasis are associated with the frequency of CD8+ T cells in etosis, as well as the occurrence of CD8-derived LETs carrying CD107a+ vesicles in the lesions. We propose that CD8+ T cell derived LETs may serve as a tool for delivering cytotoxic vesicles to distant target cells, providing insights into mechanisms of CD8+ T cell mediated pathology.

A Th2-Type Response Is Associated With Exuberant Lesions in Pregnant Women Infected With Leishmania braziliensis.

Background: Cutaneous leishmaniasis (CL) is characterized by an exaggerated inflammatory response. During pregnancy there is a decreased inflammatory response, and we have shown that pregnant women with CL develop exuberant lesions. Methods: Cytokine production by peripheral blood mononuclear cells and the frequency of cells expressing cytokines in lesions from pregnant and nonpregnant women with CL were evaluated. Results: We observed that CL lesions from pregnant women displayed a more intense cellular infiltrate, associated with an increase in neutrophils and CD4+ cells. While no difference was observed regarding the number of interferon-gamma (IFN-γ)+ cells in lesions from pregnant compared to nonpregnant women with CL, interleukin-10 (IL-10) and IL-4 expression were approximately 3-times higher in lesions in pregnant women. Main sources of IL-4 and IL-10 were CD4+ and CD68+ cells, respectively. Expression of IL-4, but not IFN-γ or IL-10, was positively correlated with the intensity of inflammatory infiltrate in lesions from pregnant women. Conclusions: These results provide evidence of an IL-4-mediated pathology in Leishmania braziliensis-infected pregnant women. These differences in lesion pathogenesis in pregnant and nonpregnant women may open possibilities for new therapies for CL treatment during pregnancy, which are currently lacking.