Adaptive immunity to SARS-CoV-2 is persistent and robust for children in COVID recovery

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection elicits an adaptive cell-mediated immune response. Many SARS-CoV-2 studies analyze peripheral blood to study the immune response. A new study currently under consideration in the Nature Portfolio Journal is analyzing peripheral blood, tonsils, and adenoids in children to understand local and systemic immune responses to SARS-CoV-2. A preprinted version of the research paper is available at the following URL: Research SquareWhile undergoing peer review.

study: Robust and sustained adaptive immune response to SARS-CoV-2 in pediatric oropharyngeal lymphoid tissue.. Image Credit: Corona Borealis Studio / Shutterstock

Local adaptive immune response

Infection and replication of SARS-CoV-2 occur in the upper respiratory tract. The lymph glands closest to the site of virus entry are the tonsils and adenoids, which are located in the nose and throat areas.Here, tissue-specific T and B cell responses are generated against SARS-CoV-2. antigen In the upper respiratory tract. Tonsillectomy and adenoidectomy are common surgery in children. Tonsils and adenoids enable the study of locally adaptive immune responses.

Cell-cell interaction in lymph glands

Activation and maturation of T and B cells in the lymph occurs in the lymph glands. T-follicular helper cells (Tfh) and B cells interact in concert to enable immunoglobulin gene class switching. This promotes the formation of germinal centers (GCs), where B cells mature, producing antibodies and memory B cells.

Studies have shown that serum antibody levels are short-lived in adults with deadly coronavirus disease 2019 (COVID-19) due to the loss of GC from the thoracic lymph nodes. Conversely, some studies have shown persistent B-cell immunity derived from GC. In addition, some studies have shown the presence of Tfh cells in organ donors of lymphatic and lung tissue.

GC response in lymphatic tissue

In this study, researchers collected peripheral blood, tonsils, and adenoids from 110 children undergoing tonsillectomy or adenoidectomy.

When tested with the RT-PCR test 72 hours before surgery, all participants were COVID-19 negative. Twenty-four participants showed evidence of previous SARS-CoV-2 infection and confirmed a positive RT-PCR test. Neutralizing antibody In serum.

Neutralizing antibodies against the early SARS-CoV-2 strain WA-1 and six other variants of interest. Epsilon, alpha, gamma, beta, iota, and delta were observed in most COVID-19 convalescent subjects. Only 9 of the 23 participants had neutralizing antibodies against the Omicron mutant.

Neutralizing antibody levels were highest for the WA-1 strain and have decreased over time since SARS-CoV-2 infection. All but two participants had SARS-CoV-2 specific B cells in peripheral blood, tonsils, and adenoids.These S + RBD + B cells specifically bind Spike protein S1 domain and receptor binding domain (RBD).

High-dimensional flow cytometry of the B cell population showed that S1 + RBD + B cells are memory B cells. Therefore, a memory B cell response was evoked and maintained in the upper respiratory tract. In addition, this response was robust as it was observed 10 months after infection.

Flow cytometric data also showed a significant portion of GCB cells among the S1 + RBD + B cells of the tonsils and adenoids. The GC structure was also confirmed by multiple immunofluorescence microscopy.

Single cell analysis of B cells

S1 + and S1-B cells were classified and characterized using CITE-seq (Transcriptome and Epitope Cell Index by Sequence) in two participants and uninfected control tissue. This measured the expression of B cell surface markers and determined the sequence of a single B cell transcriptome and B cell receptor. The results of these experiments showed that some of the S1 + B cell clones were present in both the tonsils and adenoids. SARS-CoV-2 specific clones undergo class switch and somatic hypermutation in GC.

B and T cell populations after COVID-19 in lymphoid tissue

The tonsils and adenoids of COVID-19 convalescent children had a low proportion of naive B cells and T cells. Especially in adenoids, the GCB cell population was expanded. These changes were prolonged months after SARS-CoV-2 infection.

The tonsils and adenoids had a high proportion of GC-Tfh cells and T follicular regulatory (Tfr) cells. GC-Tfh cells signal B cells to form and maintain GC. In addition, these cells had a phenotype characteristic of memory T cells present in tissues and were present within the GC. In addition, their frequency was directly proportional to the frequency of GCB cells. Multifunctional assessment of T cells using SPICE (a simplified presentation of an incredibly complex assessment) showed that Tfh cells produce cytokines that enable GC formation and B cell antibody secretion. rice field. The IFN-γ type response was particularly enriched with adenoids. These data indicate that these T cells help form and maintain a SARS-CoV-2 specific GC response.

Activated and cytotoxic T cells with increased cytokine production and GC localization were also enriched in lymphoid tissue.

T cell population after COVID-19 in blood

Peripheral blood after COVID-19 was enriched with activated Tfh cells and stem cell-like memory T cells. Blood samples also contained SARS-CoV-2 reactive T cells that were not observed in the lymphatic glands. These cells were mainly memory cells.

Activated and cytotoxic T cells with increased cytokine production and GC localization were not enriched in peripheral blood.

Lymphoid tissue viral RNA

RNA isolated from formalin-fixed, paraffin-embedded tonsils and adenoid samples and analyzed using digital droplet PCR provides evidence of SARS-CoV-2 nucleocapsid RNA in multiple samples of COVID-19 convergent tissue. Shown.

Viral copies were present even when the nasal swab was negative for SARS-CoV-2. In addition, viral RNA copy correlated with the proportion of S1 + RBD + cells in the GCB cells of the tonsils. No viral protein was detected in any of the samples.

Research limits

In this study, researchers did not have information about the date of SARS-CoV-2 infection. Some participants lacked the awareness of having COVID-19. The researchers did not have a longitudinal sample to map the duration of immune change. Antigen-specific T cells in lymphoid tissue could not be depicted. COVID-19 convalescent children underwent tonsillectomy due to sleep-disordered breathing. This can be an immune disorder and can affect the immune response to SARS-CoV-2 infection.

Conclusion

This study provides evidence of persistent, localized immunity to SARS-CoV-2. In addition, COVID-19 convalescent children showed a strong lymphoid tissue-specific adaptive immune response weeks to months after acute infection.

*Important Notices

Research Square Publish preliminary scientific reports that should not be considered definitive as they have not been peer-reviewed, guide clinical practice / health-related behaviors, and should not be treated as established information.