IL-10 Producing B Cells Dampen Protective T Cell Response and Allow Chlamydia muridarum Infection of the Male Genital Tract

Abstract

A significant proportion of individuals develop chronic, persistent and recurrent genital tract infections with <i>Chlamydia trachomatis</i>, which has been attributed to the numerous strategies that the bacterium uses to subvert host immune responses. Animal chlamydia models have demonstrated that protective immune response is mediated by CD4⁺ Th1 cytokine responses. Herein, we demonstrate that early after infecting the male genital tract, <i>C. muridarum</i> triggers the production of IL-10 by splenic and lymph node cells. In addition, <i>C. muridarum</i> triggers IL-6 and TNFα secretion. Data obtained from <i>in vitro</i> and <i>in vivo</i> experiments revealed B cells as the major IL-10 contributors. Indeed, purified B cells produced high amounts of IL-10 and also exhibited enhanced expression of inhibitory molecules such as CD39, PD-L1 and PD1 after <i>C. muridarum</i> stimulation. <i>In vitro</i> experiments performed with sorted cell subsets revealed that Marginal Zone B cells were the main IL-10 producers. <i>In vitro</i> and <i>in vivo</i> studies using TLR-deficient mice indicated that TLR4 signaling pathway was essential for IL-10 production. In addition, <i>in vivo</i> treatments to neutralize IL-10 or deplete B cells indicated that IL-10 and B cells played a significant role in delaying bacterial clearance ability. Moreover, the latter was confirmed by adoptive cell transfer experiments in which the absence of IL-10-producing B cells conferred the host a greater capability to induce Th1 responses and clear the infection. Interestingly, NOD mice, which were the least efficient in clearing the infection, presented much more Marginal Zone B counts and also enhanced TLR4 expression on Marginal Zone B cells when compared to B6 and BALB/c mice. Besides, treatment with antibodies that selectively deplete Marginal Zone B cells rendered mice more capable of inducing enhanced IFNγ responses and clearing the infection. Our findings suggest that B cells play a detrimental role in <i>C. muridarum</i> infection and that activation by innate receptors like TLR4 and IL-10 production by these cells could be used by <i>Chlamydia</i> spp. as a strategy to modulate the immune response establishing chronic infections in susceptible hosts.