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Interleukin-21 signaling is important for germinal center B-cell responses, isotype switching and generation of memory B cells. However, a role for IL-21 in antibody-mediated protection against pathogens has not been demonstrated. Here we show that IL-21 is produced by T follicular helper cells and co-expressed with IFN-γ during an erythrocytic-stage malaria infection of Plasmodium chabaudi in mice. Mice deficient either in IL-21 or the IL-21 receptor fail to resolve the chronic phase of P. chabaudi infection and P. yoelii infection resulting in sustained high parasitemias, and are not immune to re-infection. This is associated with abrogated P. chabaudi-specific IgG responses, including memory B cells. Mixed bone marrow chimeric mice, with T cells carrying a targeted disruption of the Il21 gene, or B cells with a targeted disruption of the Il21r gene, demonstrate that IL-21 from T cells signaling through the IL-21 receptor on B cells is necessary to control chronic P. chabaudi infection. Our data uncover a mechanism by which CD4+ T cells and B cells control parasitemia during chronic erythrocytic-stage malaria through a single gene, Il21, and demonstrate the importance of this cytokine in the control of pathogens by humoral immune responses. These data are highly pertinent for designing malaria vaccines requiring long-lasting protective B-cell responses.

Malaria is caused by parasites of the genus Plasmodium. All human-infecting Plasmodium species can establish long-lasting chronic infections1–5, creating an infectious reservoir to sustain transmission1,6. It is widely accepted that maintenance of chronic infection involves evasion of adaptive immunity by antigenic variation7. However, genes involved in this process have been identified in only two of five human-infecting species: P. falciparum and P. knowlesi. Furthermore, little is understood about the early events in establishment of chronic infection in these species. Using a rodent model we demonstrate that only a minority of parasites from among the infecting population, expressing one of several clusters of virulence-associated pir genes, establishes a chronic infection. This process occurs in different species of parasite and in different hosts. Establishment of chronicity is independent of adaptive immunity and therefore different from the mechanism proposed for maintainance of chronic P. falciparum infections7–9. Furthermore, we show that the proportions of parasites expressing different types of pir genes regulate the time taken to establish a chronic infection. Since pir genes are common to most, if not all, species of Plasmodium10, this process may be a common way of regulating the establishment of chronic infections.

Objective The goal of this study was to define a pharmacodynamic biomarker based on gene expression in skin that would provide a biological measure of disease extent in patients with diffuse cutaneous systemic sclerosis (dcSSc) and that could be used to monitor skin disease longitudinally. Methods Skin biopsies taken from a cohort of dcSSc patients that included longitudinal samples were analyzed by microarray. Expression of genes correlating with the modified Rodnan skin score (MRSS) were examined by nanostring for change over time, and a generalized estimating equation used to define and validate longitudinal, pharmacodynamic biomarkers composed of multiple genes. Results Microarray analysis of genes parsed to include only genes correlating with the MRSS revealed prominent clusters of profibrotic/TGFβ-regulated, IFN-regulated/proteasome, macrophage and vascular marker genes. Using genes changing longitudinally with the MRSS, two multigene, pharmacodynamic biomarkers were defined. The first was defined mathematically, applying a generalized estimating equation to longitudinal samples. This modeling method selected cross-sectional THBS1 and longitudinal THBS1 and MS4A4A genes. The second model was based on a weighted selection of genes, including additional genes with statistically significant change over time: CTGF, CD163, CCL2 and WIF1. Biomarker levels calculated using both models correlated highly with the MRSS in an independent validation dataset. Conclusion Skin gene expression can be used effectively to monitor SSc skin disease change over time. We have implemented these relatively simple models on a nanostring platform permitting highly reproducible assays that can be applied directly to samples from patients or collected as part of clinical trials.

Scleroderma (SSc) is a complex and heterogeneous connective tissue disease mainly characterized by autoimmunity, vascular damage, and fibrosis that mostly involve the skin and lungs. Epstein–Barr virus (EBV) is a lymphotropic γ-herpesvirus that has co-evolved with human species, infecting >95% of the adult population worldwide, and has been a leading candidate in triggering several autoimmune diseases. Here we show that EBV establishes infection in the majority of fibroblasts and endothelial cells in the skin of SSc patients, characterized by the expression of the EBV noncoding small RNAs (EBERs) and the increased expression of immediate-early lytic and latency mRNAs and proteins. We report that EBV is able to persistently infect human SSc fibroblasts in vitro, inducing an aberrant innate immune response in infected cells. EBV–Toll-like receptor (TLR) aberrant activation induces the expression of selected IFN-regulatory factors (IRFs), IFN-stimulated genes (ISGs), transforming growth factor-β1 (TGFβ1), and several markers of fibroblast activation, such as smooth muscle actin and Endothelin-1, and all of these genes play a key role in determining the profibrotic phenotype in SSc fibroblasts. These findings imply that EBV infection occurring in mesenchymal, endothelial, and immune cells of SSc patients may underlie the main pathological features of SSc including autoimmunity, vasculopathy, and fibrosis, and provide a unified disease mechanism represented by EBV reactivation.