647 - Tonsils serve as a reservoir for protective responses against SARS-CoV-2 in Children

Publication Number: 647.6940

Tolani Aliyu, NewYork-Presbyterian Morgan Stanley Children's Hospital, Brentwood, NY, United States; Tianci Guan, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, United States; Gowri Konkesa, Columbia University Vagelos College of Physicians and Surgeons, Parsippany, NJ, United States; Kalpana Pethe, NewYork-Presbyterian Morgan Stanley Children's Hospital, NY, NY, United States; Eli Grunstein, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, United States; Minyoung Jang, Columbia University Vagelos College of Physicians and Surgeons, NEW YORK, NY, United States; Thomas Connors, Columbia University Medical Center, New York, NY, United States

Background: Protection from SARS-CoV-2 is mediated by the establishment of long lived adaptive immune responses. Following infection or vaccination, naïve B cells become activated, proliferate, and produce immunoglobulins. A subset of B cells differentiate into plasma cells and others will become long lived memory B cells. Our current understanding of antibody and B cell responses in children is largely derived from studies on blood. As the majority of immune cells reside within mucosal and lymphoid tissue sites, accessing tissue sites can provide new insights into differences in how protection is generated and maintained across childhood. The tonsils are a mucosal associated lymphoid tissue which are directly exposed to inhaled and ingested pathogens and are removed electively. These tissues can be used to study the development of the immune system and antigen specific responses.

Objective: To define pediatric specific immune responses to SARS-CoV-2 across blood and tissue sites

Design/Methods: In this study we obtained tonsils and blood from n=25 children (aged 1.7 – 15.5 years, mean 5.2 years). We performed high dimensional flow cytometry to and ELISA to define antigen specific responses to SARS-CoV-2 virus.
Children with known immunodeficiency and chronic tonsillitis were excluded.

Results: Within the tonsil, the majority of B cells expressed a naïve, non-class switched phenotype (CD27-/IgM+/IgD+). SARS-CoV-2 specific B cells made up a small fraction of total B cells (0.01-0.07%, mean 0.04%) and predominantly displayed a naïve non-class switched phenotype. Memory CD27+ SARS-CoV-2 specific cells (1.6-29.5%, mean 11.9%) were IgM+/IgD+ (16.7-75.0%, mean 41.0%), followed by IgG+ (0-64%, mean 30.2%), IgA+ (0-16.3%, mean 6.6%), and then a small population of IgD+ single positive cells (0-7.7%, mean 3.3%). Proportions of SARS-CoV-2 specific B cells did not correlate to plasma levels of antibodies.

Conclusion(s): The majority of SARS-CoV-2 specific CD27hi B cells were double positive for IgM and IgD, a population previously identified as marginal zone-like, enriched in children, and capable of T cell independent responses. Interestingly, many subjects also had single positive IgD SARS-CoV-2 B cells, a population capable of migrating within mucosal sites, particularly the nasal cavities. Further work exploring how age-related differences alters the composition of these subsets is warranted. These results reveal the tonsil as a dynamic site for immune responses in children and shed new light on how children mediate protection against novel pathogens.