NK cells regulating T cell responses: mechanisms and outcome

• Natural killer (NK) cells can directly or indirectly regulate T cell responses in a positive or negative manner.
• Direct recognition of T cells by NK cells leads to their elimination by cytotoxicity.
• T cells have evolved mechanisms to avoid NK cell recognition.
• NK cell regulation of T cell immunity has implications for disease outcome.

Natural killer (NK) cells are important innate effectors in immunity. NK cells also have a role in the regulation of the adaptive immune response, and have been shown, in different contexts, to stimulate or inhibit T cell responses. Recent findings have expanded our understanding of the mechanisms underlying this regulation, revealing that regulation by NK cells can result from both direct interactions between NK cells and T cells, as well as indirectly, involving interactions with antigen presenting cells and the impact of NK cells on infected cells and pathogen load. We review these recent findings here, and outline emerging principles of how this regulation influences the overall outcome of adaptive immunity in infection and disease.