Abstract
The leishmaniases are diseases caused by pathogenic protozoan parasites of the genus Leishmania. Infections are initiated when a sand fly vector inoculates Leishmania parasites into the skin of a mammalian host. Leishmania causes a spectrum of inflammatory cutaneous disease manifestations. The type of cutaneous pathology is determined in part by the infecting Leishmania species, but also by a combination of inflammatory and anti-inflammatory host immune response factors resulting in different clinical outcomes. This review discusses the distinct cutaneous syndromes described in humans, and current knowledge of the inflammatory responses associated with divergent cutaneous pathologic responses to different Leishmania species. The contribution of key hematopoietic cells in experimental cutaneous leishmaniasis in mouse models are also reviewed and compared with those observed during human infection. We hypothesize that local skin events influence the ensuing adaptive immune response to Leishmania spp. infections, and that the balance between inflammatory and regulatory factors induced by infection are critical for determining cutaneous pathology and outcome of infection.
Highlights
Leishmaniasis is the group of diseases initiated through the bite of a female phlebotomine sand fly vector
Most fatalities are due to visceral leishmaniasis, in which Leishmania spp. parasites disseminate from the site of skin infection to visceral organs where they can cause pathology [3]
Subclinical infection is common in localized cutaneous leishmaniasis (LCL) and other forms of leishmaniasis, and can be detected by a lack of lesions or scars suggestive of healed CL, and lack of a history of chronic ulcer but a positive delayed type hypersensitivity (DTH) skin response to leishmanial antigen, or production of Interferon γ (IFNγ) by blood cells stimulated with Leishmania antigen, indicative of a functional cellular immune response [68,69,70]
Summary
Leishmaniasis is the group of diseases initiated through the bite of a female phlebotomine sand fly vector. Sci. 2017, 18, 1296 leishmaniasis characterized by multiple nodular lesions full of parasites It is not well defined what drives these differences in clinical outcome. Despite their different clinical manifestations, all forms of vector-borne leishmaniasis start with a similar series of events in host skin These include the initial interactions among Leishmania promastigotes, vector components, and host skin cells, all serving to influence the innate immune activation cascade. Leishmania parasites establish intracellular infection among macrophages, the primary Leishmania host cell housing a majority of parasites throughout chronic infection These local events lead to presentation of Leishmania antigen to T lymphocytes to initiate a T cell-mediated immune response. We review the different types of tegumentary leishmaniasis during infection with different Leishmania species, and examine how host cutaneous responses contribute to or protect from disease
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