Abstract. The present study was undertaken to determine the relationship between the hyaluronate receptor and CD44 (H-CAM), cell-surface glycoproteins of similar molecular weights that have been implicated in cell adhesion. In initial experiments, a panel of monoclonal antibodies directed against CD44 were tested for their ability to cross react with the hyaluronate receptor. These antibodies immunoprecipitated [3H]hyaluronate binding activity from detergent extracts of both mouse and human cells, indicating that the hyaluronate receptor is identical to CD44. In addition, one of these antibodies (KM-201 to mouse CD44) directly blocked the binding of labeled hyaluronate to the receptor and inhibited hyaluronate dependent aggregation of SV-3T3 cells.

. Integrins are heterodimeric cell surface proteins that mediate both cell-cell and cell-extracellular matrix interactions . We and others recently identified cDNAs encoding a novel integrin ß subunit, 07, in lymphocytes . We have now detected 07 mRNA in mouse TK-1 T lymphoma cells, which are known to express the putative Peyer's patch homing receptor a4ßP. We used an anti-peptide antiserum and a novel mAb against the 07 subunit to show that TK-1 cells express 07 as the only subunit associated with a4. We conclude that 07 and ßP are identical. We also show that activated peripheral blood T cells express a4ß7.We studied the function of a4ß7/a4ßP in TK-1 cells, which do not express very late antigen (VLA)-4 (a4ß1) . Cells adhered to intact fibronectin and to a fibronectin fragment containing the CS-1 region, but not to a T HE ability to interact with a variety of cells or with proteins of the extracellular matrix is crucial for a variety of leukocyte functions, including cell activation, phagocytosis, recruitment to sites of inflammation, recirculation, and homing (for reviews see Stoolman, 1989;Butcher, 1990;Springer, 1990). Many adhesion molecules expressed on T lymphocytes belong to the integrin family. Integrins are noncovalently linked heterodimers consisting of an a and a ß subunit that mediate cell-extracellular matrix as well as cell-cell interactions (Hynes, 1987;Ruoslahti, 1991) . The a and ß subunits each have a large extracellular domain, a short transmembrane region, and a cytoplasmic tail. At least 13 different a and eight different ß subunits have been identified to date; these combine to produce at least 18 different integrin heterodimers . Both a and ß subunits participate in the determination ofligand specificity. The tripeptide RGD (Arg-Gly-Asp) is the recognition site for many of the integrins that bind to extracellular matrix proteins.Members of the 01 integrin subfamily (a1ß1 to a6ß1), also referred to as the very late antigens (VLA-1 to VLA-6), bind and mediate adhesion to several extracellular matrix proteins such as laminin, collagens, and fibronectin (Hemler, 1990) .

The specificity of lymphocyte homing from the blood into a tissue is determined in part by complementary pairs of adhesion receptors on lymphocytes and endothelial cells termed homing receptors and vascular addressins, respectively. The mucosal vascular addressin involved in lymphocyte homing to Peyer's patches is a 66-kDa glycoprotein, MAdCAM-1. Investigation of the regulation and molecular genetics of MAdCAM-1 have been hampered by the lack of a murine cell line expressing this adhesion molecule. We show herein using indirect immunofluorescence studies that MAdCAM-1 can be induced on a murine endothelial cell line, bEnd.3, by cytokines and LPS. Western blot analysis of MAdCAM-1 purified by affinity column chromatography from TNF-alpha-treated bEnd.3 cells demonstrates a 66-kDa protein that comigrates in SDS-PAGE with the MAdCAM-1 constitutively found on high endothelial venules in murine mesenteric lymph nodes. Comparison of MAdCAM-1 expression on the bEnd.3 cells was made to the expression of adhesion molecules ICAM-1 and VCAM-1. MAdCAM-1 and VCAM-1 are not constitutively expressed on the bEND.3 surface but can be induced in a concentration-dependent manner by LPS, TNF-alpha, and IL-1. ICAM-1 is constitutively expressed on the endothelioma surface and expression is increased by TNF-alpha, IL-1, LPS, and IFN-gamma. Surface expression of MAdCAM-1 peaks 12 to 18 h after exposure to TNF-alpha and remains elevated at 48 h, whereas expression of VCAM-1 peaks at 4 h and inducible ICAM-1 peaks between 4 and 18 h. Interestingly, IFN-gamma has differential effects on expression of these three adhesion receptors. IFN-gamma alone induces VCAM-1 and enhances ICAM-1 expression, but does not induce MAdCAM-1. Furthermore, although, preincubation of bEND.3 cells with IFN-gamma modestly increases the induction of ICAM-1 and VCAM-1 in response to TNF-alpha and IL-1, it dramatically reduces the TNF-alpha, IL-1, and LPS-induced expression of MAdCAM-1. MAdCAM-1 on bEnd.3 cells is functional as the murine T lymphoma TK1, known to bind MAdCAM-1, also binds to TNF-alpha-stimulated endothelioma but not to unstimulated cells. This binding is blocked by the antibodies against MAdCAM-1 and against the alpha 4-chain of its integrin receptor, alpha 4 beta 7, on TK1 cells.(ABSTRACT TRUNCATED AT 400 WORDS)