Estudo da supressão bystander na infecção experimental por Leishmania amazonensis em animais geneticamente selecionados para tolerância oral: estabelecimento de protocolos para utilização em leishmaniose

Abstract

Oral tolerance (OT) is an induction of peripheral immune suppression and has been considered as a therapeutic strategy for inflammatory autoimmune diseases. Recent results (Tavares et al 2006) with strains of mice selected for extreme phenotypes of susceptibility (TS mice) and resistance (TR mice) to oral tolerance, showed differences in lesion development and parasite load after infection with Leishmania amazonensis. The bystander suppression by oral tolerance was initially described as a mechanism in which regulatory T cells triggered by an antigen-specific ingested, are capable of suppressing the response to an antigen-nonspecific, when given concurrently with antigen-specific. The TR and TS strains were used for the development of bystander suppression protocols in order to inhibit the inflammatory response induced by infection with L. amazonensis. The mice received 1, 2, 5 or 25 mg of OVA intragastrically (IG) for two consecutive days and a week later 107 were infected with promastigotes of L. amazonensis and challenged with 50 mg soluble OVA in the same place. In another protocol, mice were treated IG with OVA and challenged one week later with the same antigen followed by leishmania antigen in CFA in the same "bystander place". The following week were infected in the opposite foot. TR mice immunized with 25 mg OVA developed exaggerated inflammatory lesions when compared with the control group, while animals immunized with 1, 2 or 5 mg OVA developed a minor injury. The effect of bystander did not alter the parasite load. Regardless of the protocol used, the TS mice developed a minor injury. The cytokines IFN-y and IL-10 were increased in animals infected with both strains compared to uninfected animals. In the TR mice underwent IG OVA low-dose bystander (1, 2 and 5 mg) observed reduction of IFN-y and increased IL-10 suggesting a shift to regulatory status consistent with the reduction of inflammatory lesions in these groups. In immunized TS mice, observed a reduction of IFN-y and increased IL-10, although they remain higher than in TR, regardless of the oral dose to which they were submitted. The bystander effect with low or high doses did not alter the parasite burden. The levels of IFN-y were not associated with the reduction of parasite burden in TR and TS, since TS in the line there was a high parasite load despite high levels of IFN-y while TR strain showed a lower level of IFN- g and low parasite load. The TS strain had an inherently higher proportion of Treg cells (CD25 + Foxp3 +) that the strain TR, but animals of both strains reached the same proportion of Treg cells after infection with L. amazonensis. A better understanding of the regulatory mechanisms of innate and adaptive immunity in the early stages of infection is necessary for the development of protocols that may limit inflammation and promote the elimination of parasites.