Avaliação da Imunogenicidade de Dois Novos Imunobiológicos Candidatos a Vacina Contra Leishmaniose Visceral Canina

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Considering the importance of immunoprophylactic strategies for the control of visceral leishmaniasis, and the lack of studies concerning the cellular and humoral events that occur during vaccination in dogs, we have attempted to evaluate the immune response of a promising new vaccines candidate against canine visceral leishmaniasis (CVL). Thirty five mongrel dogs were treated within seven experimental groups as follow: (i) control group C (n = 10) received 1 ml of sterile 0.9% saline; (ii) LB group (n = 5) received 600 μg of Leishmania braziliensis promastigote protein in 1 ml sterile 0.9% saline; (iii) Sap group (n = 5) received 1 mg of saponin in 1 ml sterile 0.9% saline; (iv) LBSap group (n = 5) received 600 μg of L. braziliensis promastigote protein and 1 mg of saponin in 1 ml sterile 0.9% saline; (v) Sal group (n = 5) received sand fly gland extract (SGE) prepared from 5 acini of salivary glands of Lutzomyia longipalpis in 1 mL sterile 0.9% saline; (vi) LBSal group (n = 5) received 600 μg of L. braziliensis promastigote protein plus SGE in 1 mL sterile 0.9% saline; and (vii) the LBSapSal group (n = 5) received 600 μg of L. braziliensis promastigote protein plus 1 mg of saponin together with SGE in 1 mL sterile 0.9% saline. Each animal received three subcutaneous injections in the right flank at intervals of 4 weeks. The results obtained indicate that some dogs exhibit local swelling or mild local induration reactions, but no ulcerated lesions or other adverse reactions, after receiving saponin as an adjuvant (Sap, LBSap or LBSapSal groups). The overall tolerance of the candidate vaccines in dogs appeared to be adequate. The evaluation of immunogenicity revealed that animals treated with LBSap and LBSapSal presented higher (P <0.05) amounts of anti- Leishmania total IgG that were associated with increased (P <0.05) levels of IgG1 and IgG2, suggesting a mixed Th1/Th2 immune response. Likewise, LBSapSal elicited the production of elevated levels of anti-SGE total IgG, IgG1 and IgG2, that was previously associated in establishing an anti-immune L. chagasi response in human. Additionally, anti-SGE Western blot experiments showed predominance in the recognition of seric proteins with molecular weights of 35, 45 and 71 kDa, particularly following LBSapSal vaccination, and were related to the resistance pattern against Leishmania infection. The immunophenotypic evaluation in peripheral blood mononuclear cells (PBMC) reveal in the LBSap and LBSapSal increased (P <0.05) counts of circulating CD21+ B-cells, CD5+ T-cells and CD4+ and CD8+ T-cell subset, suggesting protective immunity against Leishmania infection as has been suggested previously for CVL. Whilst lower stimulation index by either VSA (vaccine soluble antigen) or SLcA (soluble Leishmania chagasi antigen) were recorded for the LB and Sal groups, higher cell reactivities in the presence of both stumuli were related to LBSap and LBSapSal groups. Interestingly, a negative association was demonstrated between cell reactivity and CD4+ T-lymphocytes or CD14+ monocytes following in vitro stimulation in the Sal group. These data support the hypothesis that Sal treatment inhibits CD14+ monocytes in the promotion of CD4+ T-lymphocyte activation and the induction of cell proliferation. In contrast, when in vitro cultures of peripheral blood mononuclear cells (PBMC) were stimulated with SLcA in the LBSap treatment and VSA or SLcA in the LBSapSal group, increased lymphoproliferation activity was accompanied by a higher frequency of antigen-specific CD8+ T-cells. These results support the hypothesis that induction of CD8+ T-cells may play a protective role in the mechanism of control of parasitism by Leishmania after LBSap and LBSapSal treatment associated with the antigen-specific immune response to antigens from the etiological agent of CVL. The evaluation of potential antigen presenting cells (APC) revealed increased numbers of circulating CD14+ monocytes in the LBSap and LBSapSal groups. Furthermore, the largest APC counts were associated XIII with the highest expression of MHC-I in lymphocytes in the LBSap and CD80 and MHC-I in lymphocytes in the LBSapSal, suggesting that this association could represent interaction between the innate and adaptive immune responses, reflecting an improvement in activation status during immunization. The results obtained from the analysis of nitric oxide (NO) levels (determined as nitrite) in culture supernatants stimulated by SLcA in the LBSap and in the serum of the LBSapSal confirmed the hypothesis that these vaccines induce a potential resistance profile against Leishmania infection. Our data suggested that the potential resistance profile elicited by LBSap and LBSapSal were compatible with effective control of the etiological agent of CVL.

ASSUNTO(S)

imunogenicidade imunobiológicos candidatos imunologia vacina contra leishmaniose visceral canina

ACESSO AO ARTIGO

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