T follicular helper (TFH) cells select high-affinity, antibody-producing B cells for clonal expansion in germinal centers (GCs), but the nature of their interaction is not well defined. Using intravital imaging, we found that selection is mediated by large but transient contacts between TFH and GC B cells presenting the highest levels of cognate peptide bound to major histocompatibility complex II. These interactions elicited transient and sustained increases in TFH intracellular free calcium (Ca2+) that were associated with TFH cell coexpression of the cytokines interleukin-4 and -21. However, increased intracellular Ca2+ did not arrest TFH cell migration. Instead, TFH cells remained motile and continually scanned the surface of many GC B cells, forming short-lived contacts that induced selection through further repeated transient elevations in intracellular Ca2+.

Germinal center (GC) B cells undergo affinity selection, dependent upon interactions with CD4+ follicular helper T (TFH) cells. We demonstrate that TFH cells progressed through transcriptionally and functionally distinct stages, providing differential signals for GC regulation. They initially localized proximally to mutating B cells, secreted IL-21, induced expression of the transcription factor Bcl-6 and selected high affinity B cell clones. As the GC response evolved, TFH cells extinguished IL-21 and switched to IL-4 production, showed robust CD40 ligand expression and promoted the development of antibody-secreting B cells via upregulation of the transcription factor Blimp-1. Thus, TFH cells in the B cell follicle progressively differentiated through stages of localization, cytokine production and surface ligand expression to fine-tune of the GC reaction.

Summary Control of chronic viral infections by CD8 T cells is critically dependent on CD4 help. In particular, helper-derived IL-21 plays a key role in sustaining the CD8 T cell response, however the molecular pathways by which IL-21 sustains CD8 T cell immunity remain unclear. We demonstrate that IL-21 causes a phenotypic switch of transcription factor expression in CD8 T cells during chronic viral infection characterized by sustained BATF expression. Importantly, BATF expression during chronic infection is both required for optimal CD8 T cell persistence and anti-viral effector function, and sufficient to rescue “unhelped” CD8 T cells. Mechanistically, BATF sustains the response by cooperating with IRF4, an antigen-induced transcription factor that is also critically required for CD8 T cell maintenance, to preserve Blimp-1 expression and thereby sustain CD8 T cell effector function. Collectively, these data suggest that CD4 T cells “help” the CD8 response during chronic infection via IL-21-induced BATF expression.

Tumor necrosis factor (TNF)-alpha is a pleiotropic cytokine involved in a broad spectrum of inflammatory and immune responses including proliferation, differentiation and cell death induction in several cell types. The biological effects of TNF-alpha are mediated via the cell-surface TNF receptors TNFR1 and TNFR2. Soluble forms of these two receptors, which contain the extracellular ectodomains, are proteolytically cleaved from the membrane. High levels of soluble (s) TNFR2 in serum have been documented in multiple inflammatory pathologies. We describe here a new differential spliced isoform of human TNFR2 missing exons 7 and 8, DS-TNFR2(Delta7,8). This novel isoform lacks the transmembrane and cytoplasmic domains. Expression studies with DS-TNFR2(Delta7,8) cDNA transiently transfected COS cells showed that it encodes a sTNFR2 receptor of approximately 42 kDa. Soluble DS-TNFR2(Delta7,8) blocked TNF-alpha-induced apoptosis, which suggests that it regulates TNF-alpha function by antagonizing its biological activity. An ELISA was developed that quantifies sTNFR2 generated by alternative splicing. Our data show that sTNFR2 generated by alternative splicing can be found in sera of healthy individuals, at increased levels in patients with sepsis and at high concentrations in rheumatoid arthritis patients.