Polyreactive antigen-binding B cells are the predominant cell type in the newborn B cell repertoire

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Abstract
Polyreactive antibodies bind to a variety of different self and non‐self antigens. The B cells that make these antibodies express the polyreactive Ig receptor on their surface. To determine the frequency of polyreactive antigen‐binding B cells in peripheral blood, we incubated two different antigens, one (insulin) labeled with fluorescein isothiocyanate and the other (β‐galactosidase) with phycoerythrin, with peripheral B cells. The percentage of cells that bound these antigens was determined with the fluorescence‐activated cell sorter. Approximately 21 % of adult B cells bound insulin, 28 % bound β‐galactosidase, and 11 % bound both antigens. In contrast to B cells in the adult repertoire, 49 % of B cells in cord blood bound insulin, 54 % bound β‐galactosidase, and 33 % bound both antigens. The properties of polyreactive antigen‐binding B cells in adult and cord blood were similar, except for the fact that almost all the polyreactive antigen‐binding B cells in cord blood were CD5 positive (93 %), whereas only 40 % of the polyreactive antigen‐binding B cells in adult peripheral blood were CD5 positive, indicating that the CD5 marker is not directly linked to polyreactivity. The percentage of polyreactive antigen‐binding B cells in patients with Sjögren's syndrome, systemic lupus erythematosus and rheumatoid arthritis was equal to or slightly below that found in the normal adult B cell repertoire. It is concluded that polyreactive antigen‐binding B cells are a major constituent of the normal adult B cell repertoire and are the predominant cell type in the newborn B cell repertoire.