Adaptive NK Cell Memory and Nucleosome Interference: Two Tales of the Ly49 Receptor Family

Abstract

Ly49 receptors are the canonical natural killer cell class-I major histocompatibility complex receptors expressed in mice. They have a well-defined role in natural killer cell self/non-self discrimination and in the developmental licensing of functional natural killer cells. In this thesis, I report two novel aspects of Ly49 receptor biology. First, I show that their expression may be regulated by specific nucleosome occupancy on AML-1 binding sites within the distal Ly49 promoter. This finding sheds light on a potential regulatory pathway that has thus far been unexplored in studies of the Ly49 receptor family, and highlights the Ly49 family as an ideal model system in which to study the impact of nucleosome occupancy in general. Second, I show that Ly49 receptors have a central and indispensable role in the emerging phenomenon known as adaptive natural killer cell memory. Natural killer cells have recently been observed displaying adaptive, long-lived, antigen specific memory responses comparable to T cell memory responses, but no explanatory mechanism has been discovered to describe how adaptive memory is possible in these ‘innate’ immune cells. Using Ly49-deficient mice, I show that the inhibitory, self-specific Ly49 receptors Ly49C and Ly49I are required for adaptive memory responses to chemical haptens or protein antigens. Moreover, I show that Ly49C/I binding capabilities are required during all stages of the memory response, as is antigen presentation in the context of class I major histocompatibility complex, again analogous to T cell memory responses. I present initial findings implicating these Ly49 receptors as key components of the antigen recognition process itself, and propose a mechanism based in evolutionarily ancient immunology to explain how this specificity could arise. Finally, I demonstrate that Ly49-dependent natural killer cell memory is capable of mediating powerful anti-cancer vaccination effects using an aggressive model of melanoma. Together, these findings in Ly49 family expression regulation and its functional role in adaptive NK cell responses open several new avenues of study in Ly49 receptor biology and natural killer cell immunology.