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Background: The contribution of B-cell subsets and T-B cell interaction to the pathogenesis of allergic rhinitis (AR) and mechanisms of allergen immunotherapy (AIT) remain poorly understood. This study aimed to outline circulating B-cell signature, the underlying mechanism, and its association with clinical response to AIT in patients with AR. Methods: IgD/CD27 and CD24/CD38 core gating systems were used to determine frequencies and phenotypes of B cells. Correlations between B cells, T cells, antigenspecific IgE, and disease severity in AR patients were investigated. Switched memory B cells were co-cultured with type 2 follicular helper T (Tfh2) cells and follicular regulatory T (Tfr) cells. Associations between B-cell subsets and clinical benefits of AIT were analyzed. Results: Frequencies and absolute numbers of circulating memory B cells were increased in AR patients. CD23 expression on CD19 + CD20 + CD27 + IgD − switched memory B cells was significantly enhanced and positively correlated with antigen-specific IgE levels, symptom scores, and Tfh2/Tfr cell ratio in AR patients. Compared with those from healthy controls, Tfh2 cells from AR patients had a greater capacity to induce CD23 expression on switched memory B cells via IL-4, which was unable to be sufficiently suppressed by AR-associated Tfr cells with defective IL-10 expression.

Objectives We aimed to gain an understanding of the paradox of the immunity in COVID‐19 patients with T cells showing both functional defects and hyperactivation and enhanced proliferation. Methods A total of 280 hospitalised patients with COVID‐19 were evaluated for cytokine profiles and clinical features including viral shedding. A mouse model of acute infection by lymphocytic choriomeningitis virus (LCMV) was applied to dissect the relationship between immunological, virological and pathological features. The results from the mouse model were validated by published data set of single‐cell RNA sequencing (scRNA‐seq) of immune cells in bronchoalveolar lavage fluid (BALF) of COVID‐19 patients. Results The levels of soluble CD25 (sCD25), IL‐6, IL‐8, IL‐10 and TNF‐α were higher in severe COVID‐19 patients than non‐severe cases, but only sCD25 was identified as an independent risk factor for disease severity by multivariable binary logistic regression analysis and showed a positive association with the duration of viral shedding. In agreement with the clinical observation, LCMV‐infected mice with high levels of sCD25 demonstrated insufficient anti‐viral response and delayed viral clearance. The elevation of sCD25 in mice was mainly contributed by the expansion of CD25+CD8+ T cells that also expressed the highest level of PD‐1 with pro‐inflammatory potential. The counterpart human CD25+PD‐1+ T cells were expanded in BALF of COVID‐19 patients with severe disease compared to those with modest disease. Conclusion These results suggest that high levels of sCD25 in COVID‐19 patients probably result from insufficient anti‐viral immunity and indicate an expansion of pro‐inflammatory T cells that contribute to disease severity.

Autoimmune diseases are often treated by glucocorticoids and immunosuppressive drugs that could increase the risk for infection, which in turn deteriorate disease and cause mortality. Low-dose IL-2 (Ld-IL2) therapy emerges as a new treatment for a wide range of autoimmune diseases. To examine its influence on infection, we retrospectively studied 665 patients with systemic lupus erythematosus (SLE) including about one third receiving Ld-IL2 therapy, where Ld-IL2 therapy was found beneficial in reducing the incidence of infections. In line with this clinical observation, Ld-IL2 treatment accelerated viral clearance in mice infected with influenza A virus or lymphocytic choriomeningitis virus (LCMV). Noticeably, despite enhancing anti-viral immunity in LCMV infection, Ld-IL2 treatment exacerbated CD8+ T cell-mediated immunopathology. In summary, Ld-IL2 therapy reduced the risk of infections in SLE patients and enhanced the control of viral infection, but caution should be taken to avoid the potential risk of CD8+ T cell-mediated immunopathology in severe infections.