B cell subpopulations separated by CD27 and crucial collaboration of CD27 ⁺ B cells and helper T cells in immunoglobulin production

B cell immunoglobulin production is regulated by helper T cells through direct interaction and secreted cytokines. In the present study, we functionally analyzed CD27 in cord and peripheral blood B cells. Adult peripheral blood B cells were separated into CD27 ⁺ and CD27 ^- cells, which differed in their morphology. Cord blood B cells did not express CD27, and CD27 expression on peripheral blood B cells increased with age. Only CD27 ⁺ B cells had the ability to produce immunoglobulin, which was increased by contact with a tumor necrosis factor-related transmembrane ligand, CD70. Adult peripheral blood CD27 ⁺ B cells can be further subdivided into two discrete subtypes: IgD- CD27 ⁺ and IgD ⁺ CD27 ⁺ B cells. IgD- CD27 ⁺ B cells produce IgG, IgM and IgA, whereas IgD ⁺ CD27 ⁺ B cells predominantly produce IgM. The addition of activated CD4 ⁺CD45RO T cells expressing CD70 caused down-regulation of CD27 expression on activated B cells, and this down-modulation was completely blocked by anti-CD70 monoclonal antibody, indicating direct T-B cell contact via CD27/CD70. The triggering via CD27 and CD40 additively increased the immunoglobulin production under Staphylococcus aureus Cowan strain plus interleukin-2 stimulation. Taken together, our findings demonstrate that peripheral blood B cells are separated into subpopulations by CD27 and IgD expression and that CD27 ⁺ B cells produce large amounts of immunoglobulin by interaction with the CD70 molecule.