Adaptive immunity is a fundamental component in controlling COVID-19. In this process, follicular helper T (Tfh) cells are a subset of CD4+ T cells that mediate the production of protective antibodies; however, the SARS-CoV-2 epitopes activating Tfh cells are not well characterized. Here, we identified and crystallized TCRs of public circulating Tfh (cTfh) clonotypes that are expanded in patients who have recovered from mild symptoms. These public clonotypes recognized the SARS-CoV-2 spike (S) epitopes conserved across emerging variants. The epitope of the most prevalent cTfh clonotype, S864–882, was presented by multiple HLAs and activated T cells in most healthy donors, suggesting that this S region is a universal T cell epitope useful for booster antigen. SARS-CoV-2–specific public cTfh clonotypes also cross-reacted with specific commensal bacteria. In this study, we identified conserved SARS-CoV-2 S epitopes that activate public cTfh clonotypes associated with mild symptoms.

Immune potentiators,termed adjuvants,trigger early innate immune responses to ensure the generation of robust and long-lasting adaptive immune responses of vaccines. Presented here is as tudy that takes advantage of as elfassembling small-molecule library for the development of an ovel vaccine adjuvant. Cell-based screening of the library and subsequent structural optimization led to the discovery of as imple,c hemically tractable deoxycholate derivative (molecule 6,a lso named cholicamide) whose well-defined nanoassembly potently elicits innate immune responses in macrophages and dendritic cells.F unctional and mechanistic analyses indicate that the virus-like assembly enters the cells and stimulates the innate immune response through Toll-like receptor 7(TLR7), an endosomal TLR that detects singlestranded viral RNA. As an influenza vaccine adjuvant in mice, molecule 6 was as potent as Alum, ac linically used adjuvant. The studies described here pave the way for anew approachto discovering and designing self-assembling small-molecule adjuvants against pathogens,i ncluding emerging viruses.

IL-17A is a proinflammatory cytokine produced by many types of innate immune cells and Th17 cells and is involved in the elimination of extracellularly growing microorganisms, yet the role of this cytokine in the host defense against intracellularly growing microorganisms is not well known. Cryptococcus deneoformans is an opportunistic intracellular growth fungal pathogen that frequently causes fatal meningoencephalitis in patients with impaired immune responses. In the current study, we analyzed the role of IL-17A in the host defense against C. deneoformans infection. IL-17A was quickly produced by gdT cells at an innate immune phase in infected lungs. In IL-17A gene-disrupted mice, clearance of this fungal pathogen and the host immune response mediated by Th1 cells were significantly accelerated in infected lungs compared with wild-type mice. Similarly, killing of this fungus and production of inducible NO synthase and TNF-a were significantly enhanced in IL-17A gene-disrupted mice. In addition, elimination of this fungal pathogen, Th1 response, and expression of IL-12Rb2 and IFN-g in NK and NKT cells were significantly suppressed by treatment with rIL-17A. The production of IL-12p40 and TNF-a from bone marrow-derived dendritic cells stimulated with C. deneoformans was significantly suppressed by rIL-17A. In addition, rIL-17A attenuated Th1 cell differentiation in splenocytes from transgenic mice highly expressing TCR for mannoprotein 98, a cryptococcal Ag, upon stimulation with recombinant mannoprotein 98. These data suggest that IL-17A may be involved in the negative regulation of the local host defense against C. deneoformans infection through suppression of the Th1 response.

Streptococcus pneumoniae is a major causative bacterium of community-acquired pneumonia. Dectin-2, one of the C-type lectin receptors (CLRs), was previously reported to play a pivotal role in host defense against pneumococcal infection through regulating phagocytosis by neutrophils while not being involved in neutrophil accumulation. In the present study, to elucidate the possible contribution of other CLRs to neutrophil accumulation, we examined the role of CARD9, a common adaptor molecule for signal transduction triggered by CLRs, in neutrophilic inflammatory response against pneumococcal infection. Wild-type (WT), CARD9 knockout (KO), and Dectin-2KO mice were infected intratracheally with pneumococcus, and the infected lungs were histopathologically analyzed to assess neutrophil accumulation at 24 h post-infection. Bronchoalveolar lavage fluids (BALFs) were collected at the same time point to count the neutrophils and assess the production of inflammatory cytokines and chemokines. Neutrophil accumulation was significantly decreased in CARD9KO mice, but not in Dectin-2KO mice. TNF-α, KC and MIP-2 production in BALFs were also attenuated in CARD9KO mice, but not in Dectin-2KO mice. Production of TNF-α and KC by alveolar macrophages stimulated with pneumococcal culture supernatants were significantly attenuated in CARD9KO mice, but not in Dectin-2KO mice, compared to each group's respective control mice. In addition, pneumococcus-infected CARD9KO mice showed larger bacterial burdens in the lungs than WT mice. These data indicate that CARD9 is required for neutrophil migration after pneumococcal infection as well as inflammatory cytokine and chemokine production by alveolar macrophages and suggest that a CLR distinct from Dectin-2 may be involved in this response.

The tremendous potential of trehalose glycolipids as vaccine adjuvants has incentivized the study of how the structures of these ligands relate to their Mincle-mediated agonist activities. Despite this, structure-activity work in the field has been largely empirical, and less is known about how Mincle-independent pathways might be affected by different trehalose glycolipids, and whether Mincle binding by itself can serve as a proxy for adjuvanticity. There is also much demand for more water-soluble Mincle ligands. To address this need, we prepared polyethylene glycol modified trehalose glycolipids (PEG-TGLs) with enhanced water solubility and strong murine Mincle (mMincle) binding and signaling. However, only modest cytokine and chemokine responses were observed upon the treatment of GM-CSF treated bone-marrow cells with the PEG-TGLs. Notability, no IL-1β was observed. Using RNA-Seq analysis and a representative PEG-TGL, we determined that the more water-soluble adducts were less able to activate phagocytic pathways, and hence, failed to induce IL-1β production. Taken together, our data suggests that in addition to strong Mincle binding, which is a pre-requisite for Mincle-mediated cellular responses, the physical presentation of trehalose glycolipids in colloidal form is required for inflammasome activation, and hence, a strong inflammatory immune response.