The role of B lymphocytes in coxsackievirus B3 infection

Coxsackieviruses are important human pathogens, frequently causing myocarditis, pancreatitis, and a variety of less severe diseases. B lymphocytes appear central to the interaction between these viruses and their mammalian hosts, because agammaglobulinemic humans, genetically incapable of antibody production, are susceptible to chronic infections by coxsackieviruses and related enteroviruses, such as poliovirus and echovirus. However, recent studies show that Type B coxsackievirus (CVB) infects B lymphocytes soon after infection, suggesting the possibility that these cells may play some role in virus dissemination and/or that the virus may be able to modulate the host immune response. We analyzed the role of B lymphocytes in CVB infection and confirmed that CVB infects B lymphocytes, and extended these findings to show that this is a productive infection involving approximately 1 to 10% of the cells; however, infectious center assays show that other splenocytes are infected at approximately the same frequency. Virus is readily detectable by in situ hybridization in the spleen of immunocompetent mice but is difficult to detect in mice deficient in B cells (BcKO mice), consistent with much of the splenic signal being the result of B cell infection. Surprisingly, given the extent of their infection, B cells express barely detectable levels of the murine coxsackievirus-adenovirus receptor (mCAR), suggesting that another means of cell entry may be used. We found no evidence of B cell depletion following CVB infection, indicating that this is not the explanation for the transient immunosuppression previously reported. Virus replication and dissemination are slightly delayed in BcKO mice, consistent with B cells' playing a role as an important early target of infection and/or a means to distribute the virus to many tissues. In addition, we show that BcKO mice recapitulate a central feature of human agammaglobulinemia: CVB establishes chronic infection in a variety of organs (heart, liver, brain, kidney, lung, pancreas, spleen). In most of these tissues the viral titers remain high (10(5)-10(8) plaque forming units (pfu) per gram of tissue) for the life of the mouse, and in several there is severe pathology, particularly severe myocardial fibrosis with ventricular dilation, reminiscent of the dilated cardiomyopathy seen in humans with chronic enteroviral myocarditis. Transfer of B and/or T cells from non-immune mice had no discernible effect, whereas equivalent transfers from immune mice often resulted in transient or permanent disappearance of detectable CVB.