Hamster and mouse CD25+CD4+ T cell responses to the C-terminal of leptospiral Ig-like protein A

Leptospirosis is a major public health problem in humans and animals worldwide. The variable carboxy-terminal domain 7–13 of LigA (LigAc) is currently the most promising immunogen for the leptospirosis subunit vaccine. Its protective evidence was investigated in susceptible hamsters whose immunity was mostly based on the knowledge of resistant mice. The difference in immunity of these two animals might be an obstacle to successful vaccine development. The protective immunity induced by LigAc was reported to be specific antibodies while T-cell-mediated immunity has never been investigated. We reported for the first time that hamsters and mice gave dissimilar T-cell responses. Mice and hamsters were divided into 3 groups: an adjuvant plus recombinant LigAc (rLigAc) immunized, an adjuvant-injected, and a negative control group. Immunizations were done three times at 2-week intervals. The rLigAc-specific IgG antibody titers in rLigAc immunized mice and hamsters were significantly higher than in the control groups but no significant difference between the animals. The percentages of hamster CD4⁺ T cells were significantly higher than those of mice. Mouse CD25⁺CD4⁺ T cells responded to rLigAc significantly higher than hamsters. Interestingly, the rLigAc significantly reduced the percentage of IFN-^γ+CD4⁺ cells in mice (≅30 %) and more decrease (≅70 %) was found in hamsters. Remarkably, it also reduced considerably hamster IL^-4⁺CD4⁺ T cells (≅80 %) but an extremely low decrease in mice (≅20 %). Our result indicated that mice and hamsters gave different responses to leptospiral antigens which might be the possible key that plays a role in the outcome of disease.