Early induction of interleukin-10 limits antigen-specific CD4⁺ T cell expansion, function, and secondary recall responses during persistent phagosomal infection

Diverse pathogens have evolved to survive and replicate in the endosomes or phagosomes of the host cells and establish persistent infection. Ehrlichiae are Gram-negative, intracellular bacteria that are transmitted by ticks. Ehrlichiae reside in the endosomes of the host phagocytic or endothelial cells and establish persistent infection in their vertebrate reservoir hosts. CD4⁺ T cells play a critical role in protection against phagosomal infections. In the present study, we investigated the expansion, maintenance, and functional status of antigen-specific CD4⁺ T cells during persistent Ehrlichia muris infection in wild-type and interleukin-10 (IL-10)-deficient mice. Our study indicated that early induction of IL-10 led to reduced inflammatory responses and impaired bacterial clearance during persistent Ehrlichia infection. Notably, we demonstrated that the functional production of gamma interferon (IFN-γ) by antigen-specific CD4⁺ T cells maintained during a persistent phagosomal infection progressively deteriorates. The functional loss of IFN-γ production by antigen-specific CD4⁺ T cells was reversed in the absence of IL-10. Furthermore, we demonstrated that transient blockade of IL-10 receptor during the T cell priming phase early in infection was sufficient to enhance the magnitude and the functional capacity of antigen-specific effector and memory CD4⁺ T cells, which translated into an enhanced recall response. Our findings provide new insights into the functional status of antigen-specific CD4⁺ T cells maintained during persistent phagosomal infection. The study supports the concept that a better understanding of the factors that influence the priming and differentiation of CD4⁺ T cells may provide a basis to induce a protective immune response against persistent infections.