leukotriene-b4 and Leishmaniasis--Cutaneous

Recruitment of neutrophil granulocytes to sites of infectious tissue damage is an early event in innate immune responses. Following chemotactic signals neutrophils establish a first line of defense in a swarm-like manner. Intracellular pathogens such as

Topics: Humans; Leishmania major; Leishmaniasis, Cutaneous; Leukotriene B4; Lipoxins; Neutrophils

Neutrophils mediate early responses against pathogens, and they become activated during endothelial transmigration toward the inflammatory site. In the current study, human neutrophils were activated in vitro with immobilized extracellular matrix proteins, such as fibronectin (FN), collagen, and laminin. Neutrophil activation by FN, but not other extracellular matrix proteins, induces the release of the granules' contents, measured as matrix metalloproteinase 9 and neutrophil elastase activity in culture supernatant, as well as reactive oxygen species production. Upon contact with Leishmania amazonensis-infected macrophages, these FN-activated neutrophils reduce the parasite burden through a mechanism independent of cell contact. The release of granule proteases, such as myeloperoxidase, neutrophil elastase, and matrix metalloproteinase 9, activates macrophages through TLRs, leading to the production of inflammatory mediators, TNF-α and leukotriene B4 (LTB4), which are involved in parasite killing by infected macrophages. The pharmacological inhibition of degranulation reverted this effect, abolishing LTB4 and TNF production. Together, these results suggest that FN-driven degranulation of neutrophils induces the production of LTB4 and TNF by infected macrophages, leading to the control of Leishmania infection.

Topics: Cell Degranulation; Cell Line; Coculture Techniques; Fibronectins; Humans; Leishmania; Leishmania mexicana; Leishmaniasis, Cutaneous; Leukotriene B4; Macrophages; Microscopy, Electron, Transmission; Neutrophil Activation; Neutrophils

Neutrophils are rapidly recruited to the site of Leishmania infection and play an active role in capturing and killing parasites. They are the main source of leukotriene B4 (LTB4), a potent proinflammatory lipid mediator. However, the role of LTB4 in neutrophil infection by Leishmania amazonensis is not clear. In this study, we show that L. amazonensis or its lipophosphoglycan can induce neutrophil activation, degranulation, and LTB4 production. Using pharmacological inhibitors of leukotriene synthesis, our findings reveal an LTB4-driven autocrine/paracrine regulatory effect. In particular, neutrophil-derived LTB4 controls L. amazonensis killing, degranulation, and reactive oxygen species production. In addition, L. amazonensis infection induces an early increase in Toll-like receptor 2 expression, which facilitates parasite internalization. Nuclear factor kappa B (NFkB) pathway activation represents a required upstream event for L. amazonensis-induced LTB4 synthesis. These leishmanicidal mechanisms mediated by neutrophil-derived LTB4 act through activation of its receptor, B leukotriene receptor 1 (BLT1).

Topics: Antigens, Surface; Humans; Leishmania mexicana; Leishmaniasis, Cutaneous; Leukotriene B4; Neutrophils; NF-kappa B; Reactive Oxygen Species; Receptors, Leukotriene B4; Toll-Like Receptor 2

Ex vivo culture of spleen cells from BALB/c mice infected with 2 x 10(6) Leishmania major (L. major) promastigotes were cultured with ConcanavalinA (ConA) or leishmanial antigen (L. Ag) and tested for prostaglandin E2 (PGE2) and for leukotriene B4 (LTB4), in order to study their involvement in the evolution of cutaneous leishmaniasis and the connexion with lymphokine-mediated responses. The data were compared with those obtained in BALB/c mice protected against L. major by sublethal irradiation (550 rad; cured mice). In the unprotected BALB/c mice the levels of PGE2 that were responsible for the depression of interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF alpha) Th1-associated cytokines and for the relative increase in the interleukin-4 (IL-4) became higher and higher as the lesion progressed. On the contrary, the cured mice produced levels of PGE2 similar to normal uninfected controls, high levels of TNF alpha and IFN-gamma and low levels of IL-4. Elevated levels of LTB4 were detected in the early stage of infection in the unprotected mice compared to cured ones, a sign of more intense inflammation and a stimulus for the recruitment of inflammatory cells. The observation that exogenous LTB4 was able to enhance in vitro both Th1 cytokines in cured mice and Th2 cytokines in unprotected ones suggests that LTB4 could act in the recruitment of the T cells already committed to Th1 or Th2 phenotype.

Topics: Animals; Cells, Cultured; Dinoprostone; Female; Interferon-gamma; Interleukin-4; Leishmania major; Leishmaniasis, Cutaneous; Leukotriene B4; Mice; Mice, Inbred BALB C; Spleen; Th1 Cells; Th2 Cells; Tumor Necrosis Factor-alpha; Whole-Body Irradiation