SLAM-SAP家族蛋白调节NK细胞功能获得和NKT细胞发育的机制研究

Signaling lymphatic activation molecule (SLAM) family receptors are a group of hematopoietic cell-specific membrane proteins, which regulate a variety of immunological processes, through coupling SLAM associated protein (SAP) or its homologues EWS/FLI1 activated transcript 2 homolog (EAT-2) and EAT2-related transducer (ERT). SAP gene defect can lead to severe human immunodeficiency, X-linked Lympho-proliferative disease (XLP), which involves an array of immune abnormalities, at least including compromised natural killer (NK) cell ability to destroy "unwanted" hematopoietic cells, and failed generation of NKT cells. Innate NK cells and NKT cells are two main players to eliminate transformed tumor cells and virus-infected cells. NKT cells are also involved in the pathogenesis of autoimmune disease and bridge between the innate and adaptive immunity. Our recent studies have found that complete deficiency of SAP family adaptors, including SAP, EAT-2 and ERT, decreased NK cell killing against hematopoietic cells, but enhanced to some extent NK cell cytotoxicity towards non-hematopoietic cells. Since SLAM family receptors are solely found on hematopoietic cells, rather than non-hematopoietic cells, these interesting data suggest that SAP families may participate in NK cell functional acquisition, a progress named "NK cell licensing", which is found to be MHC-I-dependent on the basis of current knowledge. In absence of MHC-I molecule, NK cell is hypo-responsive, meaning that NK cells require inhibitory Ly49 families in mice, which recognize MHC-I. We make a hypothesis that NK cell may be overly licensed though SLAM families during their early functional competence in that SLAM family receptors are all converted to be inhibitory in SAP family deficient mice. Thus, the current proposal aims to investigate how SLAM-SAP family proteins regulate NK cell licensing and NKT cell development at cellular and molecular levels. We will take advantage of our well-established experimental animal models, and utilize many approaches, involving modern immunology, genetics, in combination with biochemical methods. We try to find a novel NK cell licensing pathway that is MHC-I-independent and SLAM-family-involved, and to put forward new mechanisms regarding NKT cell positive selection in thymus, in particular to dissect the differential requirement of SAP-dependent and independent signals originated from SLAM family receptors for NKT cell generation. This proposal will lead to novel cellular and molecular mechanisms regarding XLP pathogenesis, and also reveal how SAP family regulates NK cell licensing and NKT cell development.

SLAM家族受体是一群造血细胞特异表达的免疫膜蛋白，它们通过偶联SAP或者EAT-2和ERT来调节多种免疫过程。SAP基因缺陷可导致人类严重免疫缺陷性疾病XLP，该疾病涉及包括NK细胞免疫监视能力下降和NKT细胞发育阻滞在内的多种免疫异常。本课题将研究SAP家族蛋白是如何在分子和细胞水平调节NK细胞功能获得和NKT细胞发育。我们将利用已有实验动物模型，采用现代免疫学、遗传学、生物化学分析手段，试图找到MHC-I分子非依赖、SLAM家族受体参与的NK细胞功能获得途径；阐明SLAM-SAP家族蛋白调节NKT细胞胸腺内阳性选择的细胞和分子机制；解析出SAP依赖和非依赖信号途径调节NKT细胞发育的新模式。该课题不仅有助于阐明 XLP发病的分子和细胞机制，还将揭示SAP家族蛋白在调节天然免疫细胞发育和功能获得的机制。

SLAM家族受体及其偶联蛋白特异性表达在免疫细胞，SAP缺失导致人类严重的免疫缺陷性疾病XLP。XLP病人通常NKT细胞发育，提示SLAM-SAP信号在NKT细胞发育发挥重要作用，然而由于SLAM家族受体的冗余性和SAP活性的复杂性，至今没有证据表明SLAM家族受体介导的SAP信号参与了NKT细胞发育。此外，SLAM家族受体广泛表达于NK细胞表面，是否SLAM家族受体可以介导NK细胞的功能获得目前也未知。本研究通过制备SLAM家族联合缺失小鼠，客服了SLAM家族受体冗余性导致无法全面揭示这类受体功能的瓶颈。我们发现SLAM家族受体缺陷导致NKT细胞发育严重受阻，SLAM家族受体影响早期NKT细胞的阳性选择，此外我们证明多种SLAM家族受体参与了NKT细胞发育，SLAM家族受体主要是通过激活下游的CBM复合物信号调节NKT细胞发育的。SLAM家族也可以在SAP缺失时传递抑制信号，但是该信号对NKT细胞发育作用甚微。因此，我们全面解析了SLAM家族受体双重信号对NKT细胞发育的调节作用。另一方面，我们发现SLAM家族受体缺失可以导致NK细胞的功能增加，其机制是SLAM家族受体作为自身特异性的活化受体介导NK细胞的功能驯化，丢失SLAM家族受体使得NK细胞功能变得更加敏感，因此我们首次提出了一种新的NK细胞驯化途径。这些研究对NKT和NK细胞基础生物学具有重要意义，此外对解释XLP致病机制也有促进作用。主要结果发表在Immunity和JEM上。