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Characterization of a subset of human B lymphocytes interacting with natural killer cells
1Department of Microbiology and Immunology, Duke University Medical Center, Durham, NC 27710.
Insights
Tonsil B cells directly interact with natural killer (NK) cells, activating them to produce interferon-gamma (IFN-γ). This interaction highlights NK cell cytokine production as key in regulating humoral immune responses.
Area of Science:
- Immunology
- Cell Biology
Background:
- Natural killer (NK) cells and B cells are crucial components of the immune system.
- The interaction between NK cells and B cells is complex and not fully understood.
Purpose of the Study:
- To investigate the direct interaction between human tonsil B cells and NK cells.
- To characterize the phenotype of B cells that interact with NK cells.
- To determine the functional consequences of B cell-NK cell interactions.
Main Methods:
- In vitro co-culture of tonsil B cells and NK cells.
- Detection of cell conjugation and cold target inhibition assays.
- Flow cytometry and immunofluorescence staining for cell surface markers.
- Percoll gradient fractionation to isolate cell populations.
Main Results:
- A specific, direct interaction between B cells and NK cells was observed.
- NK cell activation and subsequent interferon-gamma (IFN-γ) production were induced by B cells.
- B cells interacting with NK cells exhibited characteristics of late-stage activation (low density, bright Hoechst staining).
- The phenotype of interacting B cells (ICAM-1bri, 4F2+, TfR+, CD32+, BB1+, CD77-, CD38-) suggests a late differentiation stage.
Conclusions:
- Tonsil B cells can directly engage NK cells, leading to NK cell activation and IFN-γ production.
- NK cell-mediated cytolysis of these B cells is limited; cytokine production is likely more significant.
- NK cell-produced IFN-γ may play a crucial role in regulating humoral immune responses via B cell interactions.
Abstract:
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.