Normal macrophage functions,but impaired induction of γδ T cells,at the site of bacterial infection in CD45 exon 6-deficient mice

We investigated the protective functions of macrophages and γδ T cells in adult CD45 exon 6-deficient (CD45?/?) mice against an intraperitoneal (i.p.) infection with Listeria monocytogenes. γδ T cells are preferentially localized in the spleen, liver, and intraperitoneal cavity of the adult CD45?/? mice. Increased numbers of γδ T cells were observed after i.p. infection with L. monocytogenes in the peritoneal cavity of C57BL/6 (CD45+/+) mice but not in CD45?/? mice. The γδ T cells showed predominant usage of Vδ5 and Vδ6 rearranged to Jδ1 in the infected CD45?/? mice which are the same as those used by resident γδ T cells of noninfected CD45+/+ and CD45?/? mice. Furthermore, we analyzed the protective abilities of the CD45?/?, CD45+/+, and γδ T cell-depleted mice at the early stage of the listerial infection. The numbers of bacteria in the spleens and livers of the CD45?/? mice 5 days after the listerial infection were almost ten times larger than those in the CD45?/? and γδ T cell-depleted CD45+/+ mice. Macrophages showed normal antigen presentation, nitric oxide production and bactericidal activity for L. monocytogenes despite their lacking CD45 surface expression, suggesting that CD45-negative macrophages have a minimal influence on the increased bacterial multiplication in the CD45?/? mice. These results suggest that the γδ T cells are induced by the bacterial infection in a CD45-dependent manner, and that unresponsiveness of the γδ T cells results in only weak protection against L. monocytogenes in CD45?/? mice.