Natural killer (NK) cells are multicompetent lymphocytes of the innate immune system, whose central role in host defense, immune regulation, and autoimmunity has been increasingly recognized in the last years.
The NK cell physiology differs significantly between humans and rodents. Humans harbor two functionally distinct NK cell subsets exerting either predominantly cytolytic (CD16+CD56dim) or immunoregulatory (CD16-CD56bright) functions and utilize different receptors for NK cell activation and inhibition. The overall goal of this proposal is to define and understand the multiple roles of natural killer (NK) cells in the evolution and progression of (auto)immune-mediated damage of the human CNS with a primary focus on multiple sclerosis (MS). The hypothesis to be tested is that NK cells enhance inflammatory CNS diseases in humans, and play a pivotal role in sustaining destructive autoimmunity in MS by (i) shaping local Th1-polarized adaptive immune responses within the target tissue and via (ii) direct recognition and lysis of inflammation-activated human brain cells.
This proposal takes advantage of the respective expertises of Dr. Christian Münz (PI, Rockefeller University, New York) in immunology and innate immunity with a focus on NK cell biology, Dr. Cedric Raine (collaborator, Albert Einstein College of Medicine, New York) in neuropathology and neuroimmunology, and Dr. Fred Lublin (collaborator, Mount Sinai School of Medicine, New York) in neurology and multiple sclerosis research.
To achieve our objective, three Specific Aims are proposed:
1. To identify the mechanism by which NK cells recognize and kill human brain cells. Cytotoxicity will be determined in co-culture experiments using human fetal brain tissue–derived target cells (oligodendrocytes, microglial, astrocytes) and human NK cells in titrated effector cell to target cell (E:T) ratios. Transwell and blocking experiments will define the mechanisms by which NK cells induce CNS tissue injury in humans.
2. To determine whether NK cells are capable of shaping local adaptive immune responses within the CNS via interaction with microglial and dendritic cells (DC). The phenotypic plasticity of human quiescent and differentiated microglial cells (MG) in response to classical DC stimuli will be determined by multiparameter flow-cytometry. Co-culture with activated and phenotypically characterized human NK cells in titrated E:T ratios will determine whether NK-DC/MG interactions can directly induce DC/MG maturation. The stimulatory capacity of matured MGs and DCs will be tested by cytokine staining and in primary alloreactive T cell responses. Transwell and blockade experiments will define the mechanisms by which NK cells exert immunoregulatory effects on human MG and DC.
3. To investigate whether and to which extent NK cells participate in the formation of inflammatory CNS lesions in vivo, and to correlate NK cell phenotypes and functions in the peripheral blood and the cerebrospinal fluid (CSF) with clinical disease parameters in patients with MS and other inflammatory neurological diseases.
The proposed research aim will take advantage of the unique opportunity to study a broad set of human post mortem CNS tissue samples for the presence and distribution of NK cells in the diseased brain at the laboratory of Dr. Cedric Raine. Complementing our mechanistic in vitro-studies outlined in Specific Aims #1 and #2, cryopreserved brain samples derived from patients with MS and other CNS diseases will be characterized for the presence, distribution, and phenotype of NK cells in inflammatory brain lesions. In addition, we will characterize phenotypes and functions of NK cell derived from the blood and the CSF of patients with MS, and correlate our findings with clinical disease parameters.
Accomplishing the specific aims and the integration of the approaches outlined in this proposal might help in understanding how innate lymphocytes could sustain destructive autoimmunity in MS and will potentially provide us with a rationale for novel therapeutic strategies targeting the innate immune system in inflammatory brain diseases.