Ahnak-knockout mice show susceptibility to Bartonella henselae infection because of CD4+ T cell inactivation and decreased cytokine secretion

The present study evaluated the role of AHNAK in Bartonella henselae infection. Mice were intraperitoneally inoculated with $2{\times}10^8$ colony-forming units of B. henselae Houston-1 on day 0 and subsequently on day 10. Blood and tissue samples of the mice were collected 8 days after the final B. henselae injection. B. henselae infection in the liver of Ahnak-knockout and wild-type mice was confirmed by performing polymerase chain reaction, with Bartonella adhesion A as a marker. The proportion of B. henselae-infected cells increased in the liver of the Ahnak-knockout mice. Granulomatous lesions, inflammatory cytokine levels, and liver enzyme levels were also higher in the liver of the Ahnak-knockout mice than in the liver of the wild-type mice, indicating that Ahnak deletion accelerated B. henselae infection. The proportion of CD4+interferon-${\gamma}$ ($IFN-{\gamma}^+$) and $CD4^+$ interleukin $(IL)-4^+$ cells was significantly lower in the B. henselae-infected Ahnak-knockout mice than in the B. henselae-infected wild-type mice. In vitro stimulation with B. henselae significantly increased $IFN-{\gamma}$ and IL-4 secretion in the splenocytes obtained from the B. henselae-infected wild-type mice, but did not increase $IFN-{\gamma}$ and IL-4 secretion in the splenocytes obtained from the B. henselae-infected Ahnak-KO mice. In contrast, $IL-1{\alpha}$, $IL-1{\beta}$, IL-6, IL-10, RANTES, and tumor necrosis $factor-{\alpha}$ secretion was significantly elevated in the splenocytes obtained from both B. henselae-infected wild-type and Ahnak-knockout mice. These results indicate that Ahnak deletion promotes B. henselae infection. Impaired $IFN-{\gamma}$ and IL-4 secretion in the Ahnak-knockout mice suggests the impairment of Th1 and Th2 immunity in these mice.