Adaptive immune responses to SARS-CoV-2 persist in the pharyngeal lymphoid tissue of children

The study titled “Adaptive immune responses to SARS-CoV-2 persist in the pharyngeal lymphoid tissue of children” delves into the immune response to SARS-CoV-2, particularly focusing on the immune landscape in the upper respiratory tract. Utilizing samples from children undergoing tonsillectomy and adenoidectomy during the COVID-19 pandemic, this study provides insights into the long-term adaptive immune responses post-infection.

Here’s a detailed summary:

Study Overview:

  • Objective: To explore the adaptive immune responses to SARS-CoV-2 in the tonsils and adenoids of children post-COVID-19 infection.
  • Method: The study analyzed blood, tonsils, and adenoids from 110 children, identifying 24 samples with evidence of previous SARS-CoV-2 infection based on the presence of neutralizing antibodies, SARS-CoV-2-specific germinal center (GC), and memory B cells​​.

Key Findings:

  1. Persistent Tissue-Specific Immunity: The study observed persistent expansion of germinal center and antiviral lymphocyte populations, particularly in adenoids, indicating persistent tissue-specific immunity to SARS-CoV-2 in the upper respiratory tract of children post-infection. Viral RNA persisted in both tissues, suggesting long-term tissue-specific immune memory and potential viral remnants​​.
  2. S1+RBD+ B Cells and Memory Responses: High-dimensional flow cytometry analyses revealed that the majority of S1+RBD+ B cells were class-switched and memory B cells, present up to 10 months post-infection. These findings suggest a robust and sustained humoral memory response in the lymphoid tissues of the upper respiratory tract​​.
  3. CITE-Seq Analysis of S1+ B Cells: CITE-seq of S1-binding (S1+) and non-binding (S1−) B cells revealed distinct features of SARS-CoV-2-specific B cells. S1+ B cells were primarily IgG1 and IgA1 class-switched cells with high frequencies of somatic hypermutation and low clonal diversity, indicative of antigen-driven clonal expansion and GC origin​​.
  4. Expansion of Germinal Center Populations: Post-COVID-19 adenoids and tonsils showed expanded germinal center populations, indicating that SARS-CoV-2 infection could alter the immune landscape of mucosal tissues beyond acute infection. This was observed through unsupervised analyses and manual gating of high-dimensional flow cytometry data, comparing immune cell profiles from post-COVID-19 and uninfected control participants​​.

Conclusions and Implications: The study demonstrates that children who recover from COVID-19 have persistent adaptive immune responses in the pharyngeal lymphoid tissues, with sustained germinal center and antiviral lymphocyte populations. The presence of SARS-CoV-2-specific B cells and persistent viral RNA indicates a long-term tissue-specific immune memory. These findings underscore the importance of considering tissue-specific immunity when evaluating the overall immune response to SARS-CoV-2 and may have implications for understanding long-term immunity and potential reactivation or persistence of the virus in convalescent individuals.

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