CD49d

Abstract: The ability of lymphocyte populations to recognize and bind high endothelial venules during homing into lymphoid tissues and sites of chronic inflammation is critically dependent on their expression of certain homing-associated adhesion molecules known as homing receptors (HR). In animal models, certain lymphocyte populations, particularly subsets of memory or previously activated lymphocytes, demonstrate tissue-selective homing behavior, and it has been hypothesized that differential expression of HR accounts for this selective migration. In this study, we analyzed expression of human HR--the Dreg 56/Leu 8-defined peripheral lymph node (PLN) HR (also known as LECAM-1), H-CAM (CD44), and alpha 4-integrins (CD49d; VLA-4)--among subsets of thymocytes and peripheral blood T cells to identify populations with differential homing potential. In the thymus, these three HR classes are differentially regulated relative to phenotypically defined maturational stages, but are all expressed on the mature, surface CD3high subset. In the peripheral blood, virgin T cells (LFA-3/CD58low) show uniform high expression of the PLN HR, uniform relatively low expression of H-CAM and alpha 4-integrin, and lack markers of tissue association--the mucosal and cutaneous lymphocyte associated Ag (MLA and CLA Ags) defined by mAb Ber ACT8 and HECA-452, respectively. In contrast, circulating memory T cells (LFA-3/CD58high) are bimodal with respect to PLN HR expression, show uniform high expression of H-CAM and alpha 4-integrin, and contain essentially all the CLA and MLA Ag-bearing T cells. The circulating skin-associated T cell subset (CLA Ag+; 10 to 15% of total T cells) is predominantly PLN HR+, and shows high levels of both the alpha 4- and beta 1-integrin chains. The distinct mucosa-associated T cell subset (MLA Ag+; 1 to 3% of peripheral blood T cells) is predominantly PLN HR-; and is alpha 4high, but beta 1low. These findings indicate the independent regulation of homing-associated adhesion molecules among populations of memory/previously activated T cells, and suggest that the expression patterns of these molecules contribute to, or perhaps determine, the tissue distribution of these subsets.

Abstract: Anti-alpha 4 integrin mAb coprecipitated CD81 (TAPA-1), a 25-kDa cell surface protein, from various alpha 4 beta1 -positive hemopoietic cell lines, including Molt4, Jurkat, Ramos, and alpha 4-transfected K562 (KX4C4) cells. In reciprocal experiments, the integrin alpha 4 beta 1 (VLA4, CD49d/CD29) could be reprecipitated from CD81 immunoprecipitates. Anti-alpha 4 integrin mAb also coprecipitated CD81 from the alpha 4 beta 7-positive B cell line RPMI 8866. In contrast, no CD81 was identified in alpha 2 beta 1, alpha 5 beta 1, or alpha L beta 2 immunoprecipitates. Abs to other members of the transmembrane-4 superfamily, including CD53, CD63, and CD82, also coprecipitated alpha 4 beta 1. As shown by confocal microscopy, CD81 and CD82 colocalized with alpha 4 beta 1 in cell surface clusters. The cytoplasmic domain of the alpha 4 integrin was not necessary for alpha 4 beta 1/CD81 association, nor was the association influenced by divalent cations, EDTA, integrin-activating mAb, or alpha 4 subunit cleavage. Notably, two independent alpha 4 adhesion-deficient mutants (D346E and D408E) were deficient in their ability to associate with CD81. Thus, CD81 and other transmembrane-4 superfamily members may participate in functionally relevant interactions with alpha 4 beta 1 and other integrins.