B220− murine splenic natural killer dendritic cells (NKDC) can acquire MHC II expression and become potent stimulators of T cells (36.14)

Abstract

Abstract Introduction: NKDC (CD3−NK1.1+CD11c+B220+/−) are novel immune cells with characteristics of NK cells and DC. As NKDC exhibit broad cell surface expression of B220, we explored the functional and phenotypic differences between B220+ and B220− NKDC. Methods: Phenotype analysis was performed on wild-type (WT) and Flt3L expanded B6 splenic NKDC. WT NKDC were FACS purified based on B220 expression and used in various assays. T cell activity was measured by mixed leukocyte reaction (MLR). Supernatant IFN-γ levels were measured with a cytometric bead array. TLR9 ligand CpG (ODN 1826) and IL-18 were added to some wells. NK cells and DC were used as controls. Results: B220+ NKDC accounted for 33% of total NKDC, were larger in size, and expressed a higher level of MHC II by flow cytometry. After 24 hr culture in media alone, however, B220− NKDC gained high expression of MHC II and other co-stimulatory molecules (MHC I, CD40, CD80, CD86). Additionally, Flt3L expansion, which activates NKDC, led to a similar high level expression of MHC II on B220+ and B220− NKDC. When cultured in IL-18 and CpG for 72 hr, B220+ NKDC secreted higher levels of IFN-γ (73.3±7.4 vs. 50.1±4.1 ng/ml). Compared to B220+ NKDC, B220− NKDC caused lower allostimulation of T cells in an MLR. However, 2 hr activation with CpG prior to culture lead to an increase (and equalization) in allostimulatory capacity of both NKDC subtypes. Conclusion: B220− NKDC are an immature subtype of NKDC that possess the capacity to gain MHC II expression and become potent stimulators of allogeneic T cells.