Parasite persistence leishmaniasis in human
Parasite persistence in leishmaniasis, rather than being an exception, seems to be part of the natural history of the human Leishmania infection. The immunological response is crucial to the establishment of the process ofresolution, which will lead to clinical cure but seems unable to promote parasitological cure. Parasite persistence has been observed through PCR, a technique of high sensitivity, and has demonstrated the presence of parasite DNA in more than 80% of the scars, confirming the finding of viable parasites isolated by culture in scarred tissues. However, the mechanisms, which may favor this permanence, are not yet fully clarified, although they might be responsible for the appearance of recurrent lesions, either cutaneous or mucosal. These secondary lesions can be generated either by an exogenous orendogenous reinfection. The first hypothesis is difficult to be discarded in individuals living in endemic areas, and the second takes into account the possibility of dissemination form the primary site through a lymphatic or blood route. In the present study we have analyzed by histopathology the microenvironment of scars cured spontaneously of by specific therapy with antimonials, in the attempt to evaluate the immunopathological phenomenainvolved in the resolution process and, at the same time, in the maintenance of the parasites in the healed tissue. All the scars showed a residual inflammatory infiltrate of variable intensity but tending to reduce in parallel with the time of cure. Lymphocytes predominate in the inflammatory foci, most of them being CD4+. Functionally, there is a mixture of cytokines of type 1 and 2, with cellsexpressing IFN-amp;#947; or IL-4. The expression of IFN-amp;#947; was positively correlated with the expression of IL-4, but not IL-10, whereas iNOS, found in all cases, is directly proportional to the amount of IFN-amp;#947; and TNF-amp;#945;. There is no correlation of the expression of cytokines or phenotype with the time or kind of cure. However, parasite DNA is more frequently found in tissue scarred for less thana year as compared to those treated more than one year before, suggesting that time may be important to define parasitological cure. IL-10 was particularly more frequent in cases, which had presented secondary lesions, suggestingthat this cytokine may have an important role in the establishment of lesions due to endogenous reinfection.
School:Faculdades Oswaldo Cruz
Source Type:Master's Thesis
Keywords:Leishmania braziliensis scars human infection.
Date of Publication:11/17/2005