Plasmacytoid dendritic cell depletion leads to an enhanced mononuclear phagocyte response in lungs of mice with lethal influenza virus infection.

Plasmacytoid dendritic cells (pDCs) have been implicated both in the control and pathogenesis of influenza virus infection. We demonstrate that pDC depletion has marked effects on the response of mononuclear phagocytes, including conventional DCs (cDCs) and macrophages, to lethal influenza virus infection. Infection of mice lacking pDCs through antibody-mediated depletion resulted in substantially increased accumulation of mononuclear phagocytes and their progenitors in lungs compared to non-treated controls. pDC ablation resulted in a 5- to 35-fold enhancement of intracellular TNF-α and IL-6 production from inflammatory cDCs and exudate macrophages. Purified pulmonary cDCs and macrophages cultured from pDC-depleted mice produced significantly elevated levels of pro-inflammatory cytokines and chemokines compared to pDC-intact counterparts. Elimination of pDCs resulted in decreased lung IFN-α production and an immediate and transient reduction in lung virus burden but did not impact disease outcome. These data reveal a suppressive effect of pDCs on the inflammatory response to influenza virus infection in the lung.

Adjuvants that stimulate TLR3 or NLPR3 pathways enhance the efficiency of influenza virus-like particle vaccines in aged mice.

There is intense interest in the design and use of vaccine strategies against influenza to enhance protective immune responses in the elderly. To address the need for improved influenza vaccines for the aged, two inflammatory adjuvants, Imject(®) alum (a stimulator of the Nod-like receptor, Nalp3) and poly I:C (a toll-like receptor type 3 ligand), were used during vaccination with novel influenza virus-like particles (VLP). Adult (4 month old) or aged (24 month old) mice were vaccinated with VLPs alone or in combination with adjuvant. VLP-vaccinated adult mice were protected from a lethal influenza virus challenge without the use of either adjuvant. In contrast, only aged mice that were vaccinated with VLPs plus adjuvant survived challenge, whereas ∼33% of the mice vaccinated with VLP only survived challenge. Mice vaccinated with adjuvant only did not survive challenge despite similar levels of activation of CD11b(+)/CD11c(+) dendritic cells in the lungs. The protection was not associated with HAI titers or HA specific CD8(+) T cells, since both adjuvants boosted the VLP-induced serum HAI titers and CD8(+) responses in adult mice, but not aged mice. Influenza VLPs used in combination with two different inflammatory adjuvants during vaccination allow for the immune system to overcome the deficiency in the aged immune system to influenza virus infection.

Modeling host responses in ferrets during A/California/07/2009 influenza infection.

Immune responses during infection with pandemic H1N1 2009 influenza A virus (2009-H1N1) are still poorly understood. Using an experimental infection model in ferrets, we examined the pathological features and characterized the host immune responses by using microarray analysis, during infection with 2009-H1N1 A/California/07/2009 and seasonal A/Brisbane/59/2007. Chemokines CCL2, CCL8, CXCL7 and CXCL10 along with the majority of interferon-stimulated genes were expressed early, correlated to lung pathology, and abruptly decreased expression on day 7 following infection of A/California/07/2009. Interestingly, the drop in innate immune gene expression was replaced by a significant increase of the adaptive immune genes for granzymes and immunoglobulins. Serum anti-influenza antibodies were first observed on day 7, commensurate with the viral clearance. We propose that lung pathology in humans occurs during the innate phase of host immunity and a delay or failure to switch to the adaptive phase may contribute to morbidity and mortality during severe 2009-H1N1 infections.