IL10 and B cell deficiency: This hypothesis is supported by a previous study (10) demonstrating that B cell deficiency in mice increases the severity of histopathological changes during virulent C. burnetii NMI primary infection but did not affect the bacterial burden in spleens and our previous report that showed B1a cells secreted a high level of anti-inflammatory cytokine, IL-10 in response to C. burnetii infection in vitro (37).