Hamster IFN-γ+CD4+ and IL-4+CD4+ T cell responses against leptospires are significantly higher than those of mice.

Background: Leptospirosis is a bacterial disease caused by the Leptospira interrogans. The hamster is considered a susceptible host while the mouse is resistant. The knowledge of hamster T cell immunity is limited compared to the mouse. The reason why the hamster and the mouse give different responses to leptospires remains unclear.

Objective: To determine the differential responses of CD4+ T cells between hamsters and mice using Leptospira interrogans as an infectious model.

Methods: The CD4+ T-cell reactivity and their intracellular cytokine responses after infection with live L.interrogans serovar Autumnalis or leptospiral antigens, or injection with recombinant LipL32 protein (rLipL32) were elucidated. For secondary immune responses, mononuclear cells were re-stimulated with leptospiral crude antigens (LAg) or rLipL32. Intracellular cytokines and CD4+ T cells were determined using flow cytometry.

Results: There were no significant differences between the percentages of hamster and mouse CD4+ and CD25+CD4+ T cell responses to live bacteria. Mouse CD4+ (24.50±1.98%) and CD25+CD4+ T cells (3.83±0.88) responded significantly higher than those of hamster (15.07±2.82% and 2.00±0.37%) when infected and re-stimulated with LAg. The numbers of IFN-γ and IL-4 producing cells in hamsters at 1.76±0.10% and 0.82±0.25% for IFN-γ+CD4+ and IL-4+CD4+ T cells were significantly higher than those in resistant mice at 0.10±0.02% and 0.23±0.03% for IFN-γ+CD4+ and IL-4+CD4+ T cells.

Conclusion: Hamsters responded significantly higher in secondary stimulation especially in the levels of the IFN-γ+ and IL-4+CD4+ T cells. The mechanisms of this dissimilarity remain to be elucidated.