Influenza-specific B cell responses in HLA-DR1 transgenic mice

HLA-DR1 transgenic (DR1 Tg) mice provide a model for evaluating the breadth and specificity of CD4 T cell responses that may develop in humans following influenza infection or vaccination. Recent studies identified a tremendously broad HLA-DR1-restricted CD4 T cell responses in DR1 Tg mice infected intranasally with influenza A/New Caledonia/20/99 (NC). In this study, our goals were to characterize B cell responses after NC infection in DR1 Tg mice and establish the correlation between B cell responses and CD4 T cell responses in this system. Influenza-specific B cell responses following virus administration were analyzed in DR1 Tg mice and in the genetically matched H-2b strain C57BL/10J (B10). Following intranasal (i.n.) NC infection, B cell responses in B10 mice featured strong IgG2b and IgG2c production and were typical of previously described B cell responses to a variety of mouse-adapted influenza strains. In contrast, B cell responses in DR1 Tg mice followed delayed kinetics and were strongly skewed to IgG1 production, suggesting the Th2 polarization of CD4 T cell responses. The different antibody isotype profile in DR1 Tg mice compared to B10 mice was evident in antibody secreting cells (ASCs) frequencies and in circulating Abs levels. Surprisingly, although DR1 Tg mice had lower influenza-specific Abs levels, they exhibited higher neutralizing Abs titers early in the response. B cell responses following intranasal infection of influenza A/Puerto Rico/8/1934 (PR8) or intramuscular vaccination of inactivated NC in DR1 Tg mice were different from the observed IgG1 bias after i.n. NC infection. After i.n. PR8 infection, B cell responses were similar in DR1 Tg mice and B10 mice, characterized by predominant IgM/IgG3 production. Additionally, following intramuscular administration of inactivated NC, B cell responses were skewed towards IgG2c production in both DR1 Tg mice and B10 mice, suggesting the Th1 polarization of CD4 T cell responses. A mechanistic understanding of IgG1/Th2 biased B cell responses and better neutralizing Abs production in DR1 Tg mice following i.n. NC infection may have implications for the optimal control of influenza infection