Bartonella henselae-specific cell-mediated immune responses display a predominantly Th1 phenotype in experimentally infected C57BL/6 mice

Immune responses of the immunocompetent host to Bartonella henselae infecti on were investigated in the marine infection model using C57BL/6 mice. Foll owing intraperitoneal infection with human-derived B. henselae strain Berli n-1, viable bacteria could be recovered from livers and spleens during the first week postinfection, while Bartonella DNA remained detectable by PCR i n the liver for up to 12 weeks after infection. Granulomatous lesions devel oped in livers of infected mice, reached maximal density at 12 weeks after infection, and persisted for up to 20 weeks, indicating that B. henselae in duced a chronic granulomatous hepatitis in the immunocompetent marine host. T-cell-mediated immune responses were analyzed in vitro by means of spleen cell proliferation and cytokine release assays as well as analysis of immu noglobulin G (IgG) isotypes. Spleen cells from infected mice proliferated s pecifically upon stimulation with heat-killed Bartonella antigen. Prolifera tive responses were mainly mediated by CD4(+) T cells, increased during the , course of infection, peaked at 8 weeks postinfection, and decreased there after. Gamma interferon, but not interleukin-4, was produced in vitro by sp leen cells from infected animals upon stimulation with Bartonella antigens. Bartonella-specific IgG was detectable in serum of infected mice by 2 week s, and the antibody concentration peaked at 12 weeks postinfection. IgG2b w as the prominent isotype among the Bartonella-specific serum IgG antibodies . These data indicate that B. henselae induces cell-mediated immune respons es with a Th1 phenotype in immunocompetent C57BL/6 mice.