CD62L defines a subset of pathogen-specific bovine CD4 with central memory cell characteristics

Central memory T cells (Tcm) have not previously been characterized in cattle and any other ruminant species. Here we described two phenotypically and functionally different subsets of pathogen-specific memory CD4+ T cells in cattle that survived infection with Mycoplasma mycoides subsp. mycoides small colony (MmmSC). The first subset is CD45RO+CD45R−CD62L− and comprises two thirds of IFN-γ producing CD4+ T cells after MmmSC recall stimulation. The second is CD45RO+CD45R−CD62L+ and represents the majority of proliferating CD4+ T cells after 7 days of stimulation. Cell sorting experiments confirmed that both CD4+CD62L+ and CD4+CD62L− subsets are present in vivo and proliferate independently in recall responses to MmmSC. In addition, MmmSC stimulation strongly decreased CCR7 and increased CCR5 transcripts levels in CD4+CD62L− cells whereas CD4+CD62L+ were only slightly affected. High levels of recall proliferation but low IFN-γ production, together with the capacity to preferentially migrate through the lymph nodes (i.e., expression of CD62L and CCR7), are characteristics of Tcm, in humans and mice. Tcm are associated with long-term protective immunity and a privileged target for vaccine development. Our results demonstrate the existence of Tcm in cattle and suggest that CD62L may serve as a marker to monitor Tcm in infections and vaccine development studies in ruminant.