Kato K, Koyanagi M, Okada H, Takanashi T, Wong Y W, Williams A F, Okumura K, Yagita H
Department of Immunology, Juntendo University School of Medicine, Tokyo, Japan.
J Exp Med. 1992 Nov 1;176(5):1241-9. doi: 10.1084/jem.176.5.1241.
CD2 is an intercellular adhesion molecule that has been implicated in T cell activation and differentiation both in humans and mice. Although the ligand for human CD2 has been defined as LFA-3, that for murine CD2 has not been identified yet. To identify the ligand for mouse CD2, we generated a chimeric molecule consisting of the extracellular domain of mouse CD2 and human immunoglobulin (Ig)G1 Fc (mCD2Rg). A hamster monoclonal antibody (mAb), HM48-1, was established by screening mAbs that could block the binding of mCD2Rg to T cell lines at the ligand site. The putative mouse CD2 ligand recognized by this mAb was a glycosyl phosphatidylinositol-anchored glycoprotein with an apparent molecular mass of 45 kD, which were shared characteristics with human LFA-3. However, its expression was predominantly restricted to hematopoietic cells, unlike human LFA-3. Protein microsequencing analysis for the NH2-terminal 18 amino acid residues of the affinity-purified HM48-1 antigen revealed that it is almost identical with mouse CD48. This identity was further confirmed by the reactivity of HM48-1 with a soluble recombinant CD48 (sCD48) protein and the molecule recognized by a rat mAb raised against sCD48. A rat anti-CD48 mAb blocked the mCD2Rg binding as well as HM48-1. Moreover, sCD48 also inhibited the mCD2Rg binding to the cellular ligand. Finally, like anti-CD2 mAb, HM48-1 inhibited the phytohemagglutinin response and, when crosslinked, augmented the anti-CD3 response of splenic T cells. These results indicate that CD48 is a ligand for mouse CD2 and is involved in regulating T cell activation.
CD2是一种细胞间粘附分子，在人类和小鼠的T细胞活化及分化过程中均发挥作用。虽然人类CD2的配体已被确定为淋巴细胞功能相关抗原3（LFA-3），但小鼠CD2的配体尚未明确。为了鉴定小鼠CD2的配体，我们构建了一种嵌合分子，其由小鼠CD2的胞外结构域和人免疫球蛋白（Ig）G1 Fc段（mCD2Rg）组成。通过筛选能够在配体位点阻断mCD2Rg与T细胞系结合的单克隆抗体（mAb），获得了一种仓鼠单克隆抗体HM48-1。该单克隆抗体识别的假定小鼠CD2配体是一种糖基磷脂酰肌醇锚定糖蛋白，表观分子量为45 kD，与人LFA-3具有共同特征。然而，与人类LFA-3不同，其表达主要局限于造血细胞。对亲和纯化的HM48-1抗原的NH2末端18个氨基酸残基进行蛋白质微量测序分析，结果显示其与小鼠CD48几乎完全相同。HM48-1与可溶性重组CD48（sCD48）蛋白以及抗sCD48大鼠单克隆抗体识别的分子的反应性进一步证实了这种一致性。大鼠抗CD48单克隆抗体与HM48-1一样，均可阻断mCD2Rg的结合。此外，sCD48也可抑制mCD2Rg与细胞配体的结合。最后，与抗CD2单克隆抗体类似，HM48-1可抑制植物血凝素反应，并且在交联时可增强脾T细胞的抗CD3反应。这些结果表明，CD48是小鼠CD2的配体，并参与调节T细胞活化。
