FcγRIIB modulates splenic germinal center response against immune subversion during acute influenza A virus infection

Background: B cells are essential for providing humoral protection against acute influenza A virus (IAV) infection. FcγRIIB, a regulator of antibody (Ab) production, influences immune responses during pathogen infections, but its specific impact on humoral protection and B cell-mediated responses against IAV remains unclear. Methods: To investigate FcγRIIB's role in host defense and B cell function during acute IAV infection, we generated mice with systemic FcγRIIB deficiency, functional impairment, and B cell-specific FcγRIIB deletion. We infected these mice with PR8 (H1N1) or Hkx31 (H3N2) IAVs and evaluated body weight preservation, survival rates, Ab production, viral neutralization, Ab affinity maturation, and germinal center B cell development. Results: Mice lacking FcγRIIB or with impaired function showed improved protection, preserved body weight, and increased survival rates during IAV infection. Notably, mice with haploinsufficient FcγRIIB function displayed protective effects. Selective deficiency of FcγRIIB in B cells led to enhanced Ab production, resulting in elevated IAV-specific Abs in the serum with superior viral neutralizing potency. However, the impact on the affinity maturation index of virus-specific Abs was modest. Accordingly, FcγRIIB-deficient B cells maintained normal germinal center B cell development during IAV infection, whereas wild-type mice exhibited delayed differentiation. Conclusion: Our research underscores the pivotal role of FcγRIIB in host defense and B cell-mediated immunity during acute IAV infection. Additionally, our discoveries hold implications for antiviral treatments, particularly during the initial stages of IAV infection, aimed at enhancing the host's humoral immune response.