Amaya I. Wolf

A Promiscuous Lipid-Binding Protein Diversifies the Subcellular Sites of Toll-like Receptor Signal Transduction

The Toll-like receptors (TLRs) of the innate immune system are unusual in that individual family members are located on different organelles, yet most activate a common signaling pathway important for host defense. It remains unclear how this common signaling pathway can be activated from multiple subcellular locations. Here, we report that, in response to natural activators of innate immunity, the sorting adaptor TIRAP regulates TLR signaling from the plasma membrane and endosomes. TLR signaling from both locations triggers the TIRAP-dependent assembly of the myddosome, a protein complex that controls proinflammatory cytokine expression. The actions of TIRAP depend on the promiscuity of its phosphoinositide-binding domain. Different lipid targets of this domain direct TIRAP to different organelles, allowing it to survey multiple compartments for the presence of activated TLRs. These data establish how promiscuity, rather than specificity, can be a beneficial means of diversifying the subcellular sites of innate immune signal transduction.

Plasmacytoid Dendritic Cells Are Dispensable during Primary Influenza Virus Infection

Plasmacytoid dendritic cells (pDC) are thought to be pivotal in the first line of defense against viral infections. Although previous studies have suggested that pDC regulate the immune response against respiratory syncytial virus, their role in pulmonary infection with influenza virus has remained unclear. Using mice with GFP-tagged pDC, we observed a marked increase in pDC numbers in the lung airways 3 days after intranasal infection with influenza virus A/PR/8/34. To further investigate their potential involvement in the disease, we made use of pDC-deficient IkarosL/L mice. In the absence of pDC, the recruitment of T cells to the bronchoalveolar space was delayed, which could be reversed by the adoptive transfer of pDC before infection. Surprisingly, however, when compared with wild-type animals, IkarosL/L mice revealed a similar course of disease, as determined by weight loss, viral titers, levels of neutralizing Ab, and lung pathology. Moreover, the activation and differentiation of influenza-specific CD8+ effector T cells was unaltered in the absence of pDC, as was the generation of CD8+ memory T cells. Taken together, our study suggests that pDC regulate the accumulation of T cells in the bronchoalveolar space during early influenza virus infection, but are dispensable for the control of this disease.

Cooperativity Between CD8+ T Cells, Non-Neutralizing Antibodies, and Alveolar Macrophages Is Important for Heterosubtypic Influenza Virus Immunity

Seasonal epidemics of influenza virus result in ∼36,000 deaths annually in the United States. Current vaccines against influenza virus elicit an antibody response specific for the envelope glycoproteins. However, high mutation rates result in the emergence of new viral serotypes, which elude neutralization by preexisting antibodies. T lymphocytes have been reported to be capable of mediating heterosubtypic protection through recognition of internal, more conserved, influenza virus proteins. Here, we demonstrate using a recombinant influenza virus expressing the LCMV GP33-41 epitope that influenza virus-specific CD8+ T cells and virus-specific non-neutralizing antibodies each are relatively ineffective at conferring heterosubtypic protective immunity alone. However, when combined virus-specific CD8 T cells and non-neutralizing antibodies cooperatively elicit robust protective immunity. This synergistic improvement in protective immunity is dependent, at least in part, on alveolar macrophages and/or other lung phagocytes. Overall, our studies suggest that an influenza vaccine capable of eliciting both CD8+ T cells and antibodies specific for highly conserved influenza proteins may be able to provide heterosubtypic protection in humans, and act as the basis for a potential “universal” vaccine.

Protective antiviral antibody responses in a mouse model of influenza virus infection require TACI

Antiviral Abs, for example those produced in response to influenza virus infection, are critical for virus neutralization and defense against secondary infection. While the half-life of Abs is short, Ab titers can last a lifetime due to a subset of the Ab-secreting cells (ASCs) that is long lived. However, the mechanisms governing ASC longevity are poorly understood. Here, we have identified a critical role for extrinsic cytokine signals in the survival of respiratory tract ASCs in a mouse model of influenza infection. Irradiation of mice at various time points after influenza virus infection markedly diminished numbers of lung ASCs, suggesting that they are short-lived and require extrinsic factors in order to persist. Neutralization of the TNF superfamily cytokines B lymphocyte stimulator (BLyS; also known as BAFF) and a proliferation-inducing ligand (APRIL) reduced numbers of antiviral ASCs in the lungs and bone marrow, whereas ASCs in the spleen and lung-draining lymph node were surprisingly unaffected. Mice deficient in transmembrane activator and calcium-modulator and cyclophilin ligand interactor (TACI), a receptor for BLyS and APRIL, mounted an initial antiviral B cell response similar to that generated in WT mice but failed to sustain protective Ab titers in the airways and serum, leading to increased susceptibility to secondary viral challenge. These studies highlight the importance of TACI signaling for the maintenance of ASCs and protection against influenza virus infection.

Vaccination with M2e-Based Multiple Antigenic Peptides: Characterization of the B Cell Response and Protection Efficacy in Inbred and Outbred Mice

Background The extracellular domain of the influenza A virus protein matrix protein 2 (M2e) is remarkably conserved between various human isolates and thus is a viable target antigen for a universal influenza vaccine. With the goal of inducing protection in multiple mouse haplotypes, M2e-based multiple antigenic peptides (M2e-MAP) were synthesized to contain promiscuous T helper determinants from the Plasmodium falciparum circumsporozoite protein, the hepatitis B virus antigen and the influenza virus hemagglutinin. Here, we investigated the nature of the M2e-MAP-induced B cell response in terms of the distribution of antibody (Ab) secreting cells (ASCs) and Ab isotypes, and tested the protective efficacy in various mouse strains. Methodology/Principal Findings Immunization of BALB/c mice with M2e-MAPs together with potent adjuvants, CpG 1826 oligonucleotides (ODN) and cholera toxin (CT) elicited high M2e-specific serum Ab titers that protected mice against viral challenge. Subcutaneous (s.c.) and intranasal (i.n.) delivery of M2e-MAPs resulted in the induction of IgG in serum and airway secretions, however only i.n. immunization induced anti-M2e IgA ASCs locally in the lungs, correlating with M2-specific IgA in the bronchio-alveolar lavage (BAL). Interestingly, both routes of vaccination resulted in equal protection against viral challenge. Moreover, M2e-MAPs induced cross-reactive and protective responses to diverse M2e peptides and variant influenza viruses. However, in contrast to BALB/c mice, immunization of other inbred and outbred mouse strains did not induce protective Abs. This correlated with a defect in T cell but not B cell responsiveness to the M2e-MAPs. Conclusion/Significance Anti-M2e Abs induced by M2e-MAPs are highly cross-reactive and can mediate protection to variant viruses. Although synthetic MAPs are promising designs for vaccines, future constructs will need to be optimized for use in the genetically heterogeneous human population.

T Regulatory Cells Support Plasma Cell Populations in the Bone Marrow

Long-lived plasma cells (PCs) in the bone marrow (BM) are a critical source of antibodies after infection or vaccination, but questions remain about the factors that control PCs. We found that systemic infection alters the BM, greatly reducing PCs and regulatory T (Treg) cells, a population that contributes to immune privilege in the BM. The use of intravital imaging revealed that BM Treg cells display a distinct behavior characterized by sustained co-localization with PCs and CD11c-YFP+ cells. Gene expression profiling indicated that BM Treg cells express high levels of Treg effector molecules, and CTLA-4 deletion in these cells resulted in elevated PCs. Furthermore, preservation of Treg cells during systemic infection prevents PC loss, while Treg cell depletion in uninfected mice reduced PC populations. These studies suggest a role for Treg cells in PC biology and provide a potential target for the modulation of PCs during vaccine-induced humoral responses or autoimmunity.

Coinfection with Streptococcus pneumoniae Modulates the B Cell Response to Influenza Virus

ABSTRACT Pathogen-specific antibodies (Abs) protect against respiratory infection with influenza A virus (IAV) and Streptococcus pneumoniae and are the basis of effective vaccines. Sequential or overlapping coinfections with both pathogens are common, yet the impact of coinfection on the generation and maintenance of Ab responses is largely unknown. We report here that the B cell response to IAV is altered in mice coinfected with IAV and S. pneumoniae and that this response differs, depending on the order of pathogen exposure. In mice exposed to S. pneumoniae prior to IAV, the initial virus-specific germinal center (GC) B cell response is significantly enhanced in the lung-draining mediastinal lymph node and spleen, and there is an increase in CD4+ T follicular helper (TFH) cell numbers. In contrast, secondary S. pneumoniae infection exaggerates early antiviral antibody-secreting cell formation, and at later times, levels of GCs, TFH cells, and antiviral serum IgG are elevated. Mice exposed to S. pneumoniae prior to IAV do not maintain the initially robust GC response in secondary lymphoid organs and exhibit reduced antiviral serum IgG with diminished virus neutralization activity a month after infection. Our data suggest that the history of pathogen exposures can critically affect the generation of protective antiviral Abs and may partially explain the differential susceptibility to and disease outcomes from IAV infection in humans. IMPORTANCE Respiratory tract coinfections, specifically those involving influenza A viruses and Streptococcus pneumoniae, remain a top global health burden. We sought to determine how S. pneumoniae coinfection modulates the B cell immune response to influenza virus since antibodies are key mediators of protection.

Distinct Modes of Antigen Presentation Promote the Formation, Differentiation, and Activity of Foxp3+ Regulatory T Cells In Vivo

How the formation and activity of CD4+Foxp3+ regulatory T cells (Tregs) are shaped by TCR recognition of the diverse array of peptide:MHC complexes that can be generated from self-antigens and/or foreign Ags in vivo remains poorly understood. We show that a self-peptide with low (but not high) stimulatory potency promotes thymic Treg formation and can induce conventional CD4+ T cells in the periphery to become Tregs that express different levels of the transcription factor Helios according to anatomical location. When Tregs generated in response to this self-peptide subsequently encountered the same peptide derived instead from influenza virus in the lung-draining lymph nodes of infected mice, they proliferated, acquired a T-bet+CXCR3+ phenotype, and suppressed the antiviral effector T cell response in the lungs. However, these self-antigen–selected Tregs were unable to suppress the antiviral immune response based on recognition of the peptide as a self-antigen rather than a viral Ag. Notably, when expressed in a more immunostimulatory form, the self-peptide inhibited the formation of T-bet+CXCR3+ Tregs in response to viral Ag, and Ag-expressing B cells from these mice induced Treg division without upregulation of CXCR3. These studies show that a weakly immunostimulatory self-peptide can induce thymic and peripheral Foxp3+ Treg formation but is unable to activate self-antigen–selected Tregs to modulate an antiviral immune response. Moreover, a strongly immunostimulatory self-peptide expressed by B cells induced Tregs to proliferate without acquiring an effector phenotype that allows trafficking from the draining lymph node to the lungs and, thereby, prevented the Tregs from suppressing the antiviral immune response.