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

We investigated the protective functions of macrophages and gamma delta T cells in adult CD45 exon 6-deficient (CD45 -/-) mice against an intraperitoneal (i.p.) infection with Listeria monocytogenes. gamma delta T cells are preferentially localized in the spleen, liver, and intraperitoneal cavity of the adult CD45-/- mice. Increased numbers of gamma delta 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 gamma delta T cells showed predominant usage of V delta 5 and V delta 6 rearranged to J delta 1 in the infected CD45 -/- mice which are the same as those used by resident gamma delta T cells of noninfected CD45 +/+ and CD45 -/- mice. Furthermore, we analyzed the protective abilities of the CD45 -/-, CD45 +/+, and gamma delta 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 gamma delta 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 gamma delta T cells are induced by the bacterial infection in a CD45-dependent manner, and that unresponsiveness of the gamma delta T cells results in only weak protection against L. monocytogenes in CD45 -/- mice.