The role of influenza virus neuraminidase in modulation of the immune response

The objective of this study was to understand the role of influenza virus neuraminidase (NA) in the regulation of immune responses. Our hypothesis was that influenza virus NA alters T cell proliferation as well as cytokine production. To test our hypothesis, we established an in vitro allogeneic culture system containing bone marrow-derived H2b dendritic cells (DC) and purified H2d T cells, and compared T cell responses to influenza virus-infected or NA-treated DC with responses to untreated DC. Results obtained from these studies were as follows: (1) The magnitude of allogeneic T cell proliferation to influenza virus (A/PR/8/34 (PR8))-infected DC was dependent on the dose of virus. (2) At low virus doses, NA activity on the DC surface resulted in increased allogeneic T cell proliferation. (3) At high virus doses, activation of latent TGFbeta-1 by NA resulted in decreased allogeneic T cell proliferation. Dose-dependent differences in cluster formation, rate of DC apoptosis, and production of inhibitory cytokines TGFbeta-1 and IL-10, were observed. (4) The cellular target of viral NA dictated the quality of the allogeneic T cell response. IL-2 and gamma-IFN were optimally produced in response to low dose infected DC, while IL-4 and IL-10 were optimally produced to DC infected with high doses of PR8. Increased secretion of IL-2 and gamma-IFN required desialylation of DC, while IL-4 and IL-10 production required desialylation of T cells. (5) T cells treated with NA, or responding to allogeneic DC infected with high doses of PR8, had altered ligation of CD40L. This NA-dependent change amplified the CD40-CD40L interaction, accentuating the secretion of IL-4 and decreasing gamma-IFN secretion. (6) Viral NA treatment of DC facilitated the activation of CD8+ T cells. Unlike CD4+ T cells, the CD8+ T cell response to PR8-infected DC was not dependent on infection dose. Viral NA treatment of DC resulted in increased CD8+ T cell proliferation and cytolytic activity. Proliferation was supported by the addition of IL-4, but inhibited by gamma-IFN.; These results support our hypothesis and show that viral NA plays an important role in the regulation of in vitro immune responses. Future studies will examine in vivo T cell responses to NA-treated DC, with the goal of developing NA as a vaccine adjuvant.