Acute influenza infection has been reported to be associated with neurological symptoms. However, the long-term consequences of an infection with neurotropic and non-neurotropic influenza A virus (IAV) variants for the CNS remain elusive. We can show that spine loss in the hippocampus after infection with neurotropic H7N7 (rSC35M) and non-neurotropic H3N2 (maHK68) in female C57BL/6 mice persists well beyond the acute phase of the disease. Although spine number was significantly reduced at 30 d postinfection (dpi) with H7N7 or H3N2, full recovery could only be observed much later at 120 dpi. Infection with H1N1 virus, which was shown previously to affect spine number and hippocampus-dependent learning acutely, had no significant long-term effects. Spine loss was associated with an increase in the number of activated microglia, reduced long-term potentiation in the hippocampus, and impairment in spatial memory formation, indicating that IAV-associated inflammation induced functional and structural alterations in hippocampal networks. Transcriptome analyses revealed regulation of many inflammatory and neuron- and glia-specific genes in H3N2- and H7N7-infected mice at day 18 and in H7N7-infected mice at day 30 pi that related to the structural and functional alterations. Our data provide evidence that neuroinflammation induced by neurotropic H7N7 and infection of the lung with a non-neurotropic H3N2 IAV result in long-term impairments in the CNS. IAV infection in humans may therefore not only lead to short-term responses in infected organs, but may also trigger neuroinflammation and associated chronic alterations in the CNS. In the acute phase of influenza infection, neuroinflammation can lead to alterations in hippocampal neuronal morphology and cognitive deficits. The results of this study now also provide evidence that neuroinflammation induced by influenza A virus (IAV) infection can induce longer-lasting, virus-specific alterations in neuronal connectivity that are still detectable 1 month after infection and are associated with impairments in spatial memory formation. IAV infection in humans may therefore not only lead to short-term responses in infected organs, but may also trigger neuroinflammation and associated chronic alterations in the CNS.

Objective. Rituximab is a therapeutic anti-CD20 antibody used for in vivo depletion of B cells in proliferative and autoimmune diseases. However, the mechanisms of action are not fully understood, since not all of the therapy-mediated effects can be explained by the depletion of antibody-secreting cells. In addition to B cells, there is also a small population of T cells coexpressing CD20 in all individuals. This study was conducted to examine the phenotype and function of CD3؉CD20؉ T cells in patients with rheumatoid arthritis (RA) and healthy controls.Methods. The phenotype and apoptosis of peripheral blood mononuclear cells from healthy donors and RA patients were examined by 4-color fluorescenceactivated cell sorting analyses. Cytokine production was determined by intracellular staining and measurement of cytokines in the supernatants. Proliferation of sorted T cell populations was analyzed using 3 H-thymidine uptake assays.Results. In healthy individuals, 0.1-6.8% of peripheral blood T cells (mean 1.6%; n ‫؍‬ 142) coexpressed CD20, which was not significantly different from that in the peripheral blood of RA patients, in whom 0.4-2.6% of T cells (mean 1.2%; n ‫؍‬ 27) were CD20؉. During rituximab therapy, the CD20؉ T cells along with the B cells were eliminated from the RA peripheral blood. Among the CD20؉ T cells, 45% coexpressed CD8 and 55% coexpressed CD4. Polyclonal CD3؉CD20؉ cells were functionally characterized by constitutive cytokine production (i.e., interleukin-1␤ and tumor necrosis factor ␣), a low proliferative capacity, a high activation state, and enhanced susceptibility to apoptosis.Conclusion. These findings suggest that CD20؉ T cells represent a terminally differentiated cell type with immune-regulatory and proinflammatory capacities. Depletion of CD20؉ T cells may be an additional mechanism by which anti-CD20 therapy functions in patients with RA.

Influenza A virus (IAV) infection represents a global threat causing seasonal outbreaks and pandemics. Additionally, secondary bacterial infections, caused mainly by Streptococcus pneumoniae, are one of the main complications and responsible for the enhanced morbidity and mortality associated with IAV infections. In spite of the significant advances in our knowledge of IAV infections, holistic comprehension of the interplay between IAV and the host immune response (IR) remains largely fragmented. During the last decade, mathematical modeling has been instrumental to explain and quantify IAV dynamics. In this paper, we review not only the state of the art of mathematical models of IAV infection but also the methodologies exploited for parameter estimation. We focus on the adaptive IR control of IAV infection and the possible mechanisms that could promote a secondary bacterial coinfection. To exemplify IAV dynamics and identifiability issues, a mathematical model to explain the interactions between adaptive IR and IAV infection is considered. Furthermore, in this paper we propose a roadmap for future influenza research. The development of a mathematical modeling framework with a secondary bacterial coinfection, immunosenescence, host genetic factors and responsiveness to vaccination will be pivotal to advance IAV infection understanding and treatment optimization.

The consequences of influenza virus infection are generally more severe in individuals over 65 years of age (the elderly). Immunosenescence enhances the susceptibility to viral infections and renders vaccination less effective. Understanding age-related changes in the immune system is crucial in order to design prophylactic and immunomodulatory strategies to reduce morbidity and mortality in the elderly. Here, we propose different mathematical models to provide a quantitative understanding of the immune strategies in the course of influenza virus infection using experimental data from young and aged mice. Simulation results suggested a central role of CD8 ؉ T cells for adequate viral clearance kinetics in young and aged mice. Adding the removal of infected cells by natural killer cells did not improve the model fit in either young or aged animals. We separately examined the infection-resistant state of cells promoted by the cytokines alpha/beta interferon (IFN-␣/␤), IFN-␥, and tumor necrosis factor alpha (TNF-␣). The combination of activated CD8؉ T cells with any of the cytokines provided the best fits in young and aged animals. During the first 3 days after infection, the basic reproductive number for aged mice was 1.5-fold lower than that for young mice (P < 0.05). IMPORTANCEThe fits of our models to the experimental data suggest that the increased levels of IFN-␣/␤, IFN-␥, and TNF-␣ (the "inflammaging" state) promote slower viral growth in aged mice, which consequently limits the stimulation of immune cells and contributes to the reported impaired responses in the elderly. A quantitative understanding of influenza virus pathogenesis and its shift in the elderly is the key contribution of this work.

An infection represents a highly dynamic process involving complex biological responses of the host at many levels. To describe such processes at a global level, we recorded gene expression changes in mouse lungs after a non-lethal infection with influenza A virus over a period of 60 days. Global analysis of the large data set identified distinct phases of the host response. The increase in interferon genes and up-regulation of a defined NK-specific gene set revealed the initiation of the early innate immune response phase. Subsequently, infiltration and activation of T and B cells could be observed by an augmentation of T and B cell specific signature gene expression. The changes in B cell gene expression and preceding chemokine subsets were associated with the formation of bronchus-associated lymphoid tissue. In addition, we compared the gene expression profiles from wild type mice with Rag2 mutant mice. This analysis readily demonstrated that the deficiency in the T and B cell responses in Rag2 mutants could be detected by changes in the global gene expression patterns of the whole lung. In conclusion, our comprehensive gene expression study describes for the first time the entire host response and its kinetics to an acute influenza A infection at the transcriptome level.