Evidence for a prescribed NK cell Ly49 developmental pathway in mice

Abstract

Abstract Previous studies of NK cell Ly49 receptors suggest that the inhibitory receptor expression is stochastic. However, similar studies of activating Ly49 receptors have not been an area of focus. We hypothesize that the expression of activating receptors is not stochastic. We analyzed NK cell “clusters” expressing 16 combinations of Ly49I, Ly49G2, Ly49H and Ly49D in B6 mice. We sorted the 16 clusters, and cultured them with IL-15 for 6 days. In parallel, we also transplanted a select group of clusters in vivo. We discovered a prescribed pathway of cluster transitions in vitro and in vivo, and these data suggest that Ly49 activating receptor acquisition is not stochastic. We found that the majority of clusters that express activating receptors maintain their expression. In addition, Ly49D, which is not reported to have an MHC-I ligand in B6 mice, was upregulated on clusters that transition in the prescribed pathway. Previously, other groups have used the product rule to mathematically predict the independent expression of Ly49 inhibitory receptors. However, the product rule has not been applied to predict activating Ly49 receptor frequencies. Our application of the product rule to our data suggest that Ly49H and Ly49D expression is not independent and cannot be predicted by this mathematical model. This suggests that the biological system that controls the Ly49 activating receptors is distinct from inhibitory receptors. Currently we are investigating whether MHC-I is critical in the prescribed pathway via the transplantation of these clusters in MHC-I-deficient mice. Taken together, these data support the idea that NK cell clusters develop in a sequential, non-random manner that is determined by expression of activating Ly49 receptors.