Mehta I K, Smith H R, Wang J, Margulies D H, Yokoyama W M
Immunology Program and Rheumatology Division, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Cell Immunol. 2001 Apr 10;209(1):29-41. doi: 10.1006/cimm.2001.1786.
Ly49D is a natural killer (NK) cell activation receptor that is responsible for differential mouse inbred strain-determined lysis of Chinese hamster ovary (CHO) cells. Whereas C57BL/6 NK cells kill CHO, BALB/c-derived NK cells cannot kill because they lack expression of Ly49D. Furthermore, the expression of Ly49D, as detected by monoclonal antibody 4E4, correlates well with CHO lysis by NK cells from different inbred strains. However, one discordant mouse strain was identified; C57L NK cells express the mAb 4E4 epitope but fail to lyse CHO cells. Herein we describe a Ly49 molecule isolated from C57L mice that is recognized by mAb 4E4 (anti-Ly49D). Interestingly, this molecule shares extensive similarity to Ly49D(B6) in its extracellular domain, but its cytoplasmic and transmembrane domains are identical to the inhibitory receptor Ly49A(B6), including a cytoplasmic ITIM. This molecule bears substantial overall homology to the previously cloned Ly49O molecule from 129 mice the serologic reactivity and function of which were undefined. Cytotoxicity experiments revealed that 4E4(+) LAK cells from C57L mice failed to lyse CHO cells and inhibited NK cell function in redirected inhibition assays. MHC class I tetramer staining revealed that the Ly49O(C57L)-bound H-2D(d) and lysis by 4E4(+) C57L LAK cells is inhibited by target H-2D(d). The structural basis for ligand binding was also examined in the context of the recent crystallization of a Ly49A-H-2D(d) complex. Therefore, this apparently "chimeric" Ly49 molecule serologically resembles an NK cell activation receptor but functions as an inhibitory receptor.
Ly49D是一种自然杀伤（NK）细胞激活受体，负责不同小鼠近交系对中国仓鼠卵巢（CHO）细胞的差异性裂解。C57BL/6 NK细胞能够裂解CHO细胞，而源自BALB/c的NK细胞则无法裂解，因为它们缺乏Ly49D的表达。此外，用单克隆抗体4E4检测到的Ly49D表达与来自不同近交系的NK细胞对CHO细胞的裂解密切相关。然而，发现了一个不一致的小鼠品系；C57L NK细胞表达单克隆抗体4E4表位，但无法裂解CHO细胞。在此，我们描述了一种从C57L小鼠中分离出的Ly49分子，它可被单克隆抗体4E4（抗Ly49D）识别。有趣的是，该分子在其胞外结构域与Ly49D（B6）具有广泛的相似性，但其胞质和跨膜结构域与抑制性受体Ly49A（B6）相同，包括一个胞质免疫酪氨酸抑制基序（ITIM）。该分子与先前从129小鼠中克隆的Ly49O分子具有高度的整体同源性，其血清学反应性和功能尚未明确。细胞毒性实验表明，来自C57L小鼠的4E4（+）淋巴因子激活的杀伤细胞（LAK）无法裂解CHO细胞，并且在重定向抑制试验中抑制NK细胞功能。MHC I类四聚体染色显示，Ly49O（C57L）结合H-2D（d），并且4E4（+）C57L LAK细胞的裂解受到靶细胞H-2D（d）的抑制。还在最近Ly49A-H-2D（d）复合物结晶的背景下研究了配体结合的结构基础。因此，这种明显“嵌合”的Ly49分子在血清学上类似于NK细胞激活受体，但发挥抑制性受体的功能。
