Characterization of a subset of human B lymphocytes interacting with natural killer cells

Tonsil B cells were analyzed for their capacity to interact directly with NK cells in vitro. A specific, direct interaction between NK cells and B cells could be detected by direct conjugation and by cold target inhibition using the B lymphoblastoid cell line BJA.B as a labeled target. The data further suggest that the B cell interaction with NK cells specifically activates the NK effectors and induces their production of IFN-gamma. The NK-interactive population of tonsil B cells were characterized as low-buoyant density cells (by Percoll gradient fractionation) that stained more brightly with Hoechst 33342, both characteristics of activated B cells. Immunofluorescent staining of NK cell-B cell conjugates allowed determination of the cell-surface antigenic phenotype of conjugate-forming B cells. B cell targets were ICAM-1bri, 4F2+, TfR+, CD32+, BB1+, and CD77-. They tended to be CD38-, but overlapped the CD38+ population. No correlation was seen with CD37, CD44, CD75, CD76, HC2, or Ig kappa. This phenotype is most consistent with a late activation stage of differentiation, just before and overlapping the expression of CD38. These B cells do not appear significantly sensitive to NK-mediated cytolysis, suggesting that NK cell cytokine synthesis and secretion (e.g., IFN-gamma) may be more important in the NK cell regulation of the humoral response.