CD21-/low B cells in human blood are memory cells

• The complement receptor 2 (CR2, CD21) is part of a complex (CD21/CD19/CD81) acting as a co-receptor to the B-cell receptor (BCR). Simultaneous triggering of the BCR and CD21 lowers the threshold for B-cell activation. Although CD21 is important, B cells that express low amounts or lack surface CD21 (CD21-/low) are increased in conditions with chronic inflammation, e.g. autoimmune diseases. However, little is known about the CD21-/low B-cell subset in peripheral blood from healthy donors. Here, we show that CD21-/low cells represent around 5% of B cells in peripheral blood from adults but are barely detectable in cord blood, after excluding transitional B cells. The CD21-/low subset can be divided into CD38-24+ and CD38-24low cells, where most of the CD38-24+ are CD27+IgM+IgD+ and the CD38-24low are switched CD27-. Expression levels of additional markers, e.g. CD95 and CD62L, are similar to those on classical memory B cells. In contrast to naïve cells, the majority of CD21-/low cells lack expression of the ABCB1 transporter. Stimulation with a combination of BCR, toll-like receptor (TLR) 7/8 and IL-2 induces proliferation and differentiation of the CD21-/low B-cells comparable to CD21+CD27+ memory B cells. The response excluding BCR agonist is not on par with that of classical memory B cells, though clearly above that of naïve B cells. This is ascribed to a weaker response by the CD38-24low subset, implying that some memory B cells require not only TLR but also BCR triggering. We conclude that the CD21-/low B cells in healthy donors are memory B cells.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Immunologi inom det medicinska området (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Immunology in the medical area (hsv//eng)

Nyckelord

B cells

CD21

immunological memory

peripheral blood

TLR

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