CD21- CD27- Atypical B Cells in a Pediatric Cohort Study: An Extensive Single Center Flow Cytometric Analysis

Francesco Corrente; Sara Terreri; Patrizia Palomba; Claudia Capponi; Mattia Mirabella; Carlo Federico Perno; Rita Carsetti

doi:10.3389/fped.2022.822400

CD21^- CD27^- Atypical B Cells in a Pediatric Cohort Study: An Extensive Single Center Flow Cytometric Analysis

Front Pediatr. 2022 Jun 3:10:822400. doi: 10.3389/fped.2022.822400. eCollection 2022.

Authors

Francesco Corrente¹, Sara Terreri², Patrizia Palomba¹, Claudia Capponi¹, Mattia Mirabella¹, Carlo Federico Perno^{1

3}, Rita Carsetti^{1

2}

Affiliations

¹ Microbiology and Diagnostic Immunology Unit, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy.
² Diagnostic Immunology Research Unit, Multimodal Medicine Research Area, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy.
³ Multimodal Medicine Research Area, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy.

Abstract

Atypical B cells (atBCs) are a distinct B-cell population and represent approximately 5% of B cells in peripheral blood (PB) of healthy adult individuals. However, in adults these cells are expanded in conditions of chronic infections, inflammation, primary immunodeficiencies, autoimmune diseases, and aging. Their immunophenotype is characterized by the lack of CD21 expression and the hallmark human memory B-cell marker CD27. In this study, we investigated the immunophenotype of atBCs in different pediatric pathological conditions and correlated their expansion with the children's clinical diagnosis. We were able to retrospectively evaluate 1,571 consecutive PB samples, corresponding to 1,180 pediatric patients, by using a 9-color flow-cytometric panel. The results, compared with a pediatric healthy cohort, confirmed an expansion of atBCs in patient samples with percentages greater than 5% of total B cells. Four subpopulations with different expressions of IgM and IgD were discriminated: IgM⁺IgD⁺, IgM⁺-only, IgD⁺-only, and IgM^-IgD^-. IgG⁺ atBCs were predominant in the IgM^- IgD^- subpopulation. Moreover, the study highlighted some features of atBCs, such as a low CD38 expression, a heterogeneity of CD24, a high expression of CD19 and a large cell size. We also demonstrated that an increase of atBCs in a pediatric cohort is correlated with immunodeficiencies, autoimmune, inflammatory, and hematological disorders, consistent with previous studies mainly performed in adults. Furthermore, our flow cytometric clustering analysis corroborated the recent hypothesis of an alternative B origin for atBCs.

Keywords: B cell subsets; CD21 B cells low; atypical B cells; autoimmune diseases; flow cytometry; hematological disorders; immunodeficiencies; inflammatory diseases.