The phenotype of HLA-binding B cells from sensitized kidney transplant recipients correlates with clinically prognostic patterns of interferon-γ production against purified HLA proteins.

B cells play crucial roles in cell-mediated alloimmune responses. In vitro, B cells can support or regulate indirect T-cell alloreactivity in response to donor antigens on ELISpot and these patterns associate with clinical outcome. Previous reports of associations between B-cell phenotype and function have examined global phenotypes and responses to polyclonal stimuli. We hypothesized that studying antigen-specific B cells, using samples from sensitized patients, would inform further study to identify novel targets for intervention. Using biotinylated HLA proteins, which bind HLA-specific B cells via the B-cell receptor in a dose-dependent fashion, we report the specific phenotype of HLA-binding B cells and define how they associated with patterns of anti-HLA response in interferon-γ ELISpot. HLA-binding class-switched and IgMCD27 memory cells associated strongly with B-dependent interferon-γ production and appeared not suppressible by endogenous Tregs. When the predominant HLA-binding phenotype was naïve B cells, the associated functional ELISpot phenotype was determined by other cells present. High numbers of non-HLA-binding transitional cells associated with B-suppressed interferon-γ production, especially if Tregs were present. However, high frequencies of HLA-binding marginal-zone precursors associated with B-dependent interferon-γ production that appeared suppressible by Tregs. Finally, non-HLA-binding marginal zone precursors may also suppress interferon-γ production, though this association only emerged when Tregs were absent from the ELISpot. Thus, our novel data provide a foundation on which to further define the complexities of interactions between HLA-specific T and B cells and identify new targets for intervention in new therapies for chronic rejection.