In Vivo Identification and Characterization of CD4+ Cytotoxic T Cells Induced by Virulent Brucella abortus Infection

CD4 + T cells display a variety of helper functions necessary for an efficient adaptive immune response against bacterial invaders. This work reports the in vivo identification and characterization of murine cytotoxic CD4 + T cells (CD4 + CTL) during Brucella abortus infection. These CD4 + CTLs express granzyme B and exhibit immunophenotypic features consistent with fully differentiated T cells. They express CD25, CD44, CD62L ,CD43 molecules at their surface and produce IFN-γ. Moreover, these cells express neither the co-stimulatory molecule CD27 nor the memory T cell marker CD127. We show here that CD4 + CTLs are capable of cytolytic action against Brucella -infected antigen presenting cells (APC) but not against Mycobacterium -infected APC. Cytotoxic CD4 + T cell population appears at early stages of the infection concomitantly with high levels of IFN-γ and granzyme B expression. CD4 + CTLs represent a so far uncharacterized immune cell sub-type triggered by early immune responses upon Brucella abortus infection.