Two monoclonal antibodies (MC631 and MC813‐70) raised against 4‐ to 8‐cell stage mouse embryos and a human teratocarcinoma cell line, respectively, detect the stage‐specific embryonic antigens, the previously defined SSEA‐3 and SSEA‐4, described herein. These antibodies were both reactive with a unique globo‐series ganglioside with the structure shown below: (formula; see text) The antibodies were found to recognize sequential regions of this ganglioside, i.e., MC813‐70 recognizes the terminal ‘a’ structure whereas antibody MC631 recognizes the internal ‘b’ structure. Thus, a set of two antibodies defines this unique embryonic antigen. During differentiation of human teratocarcinoma 2102Ep cells, the globo‐series glycolipids defined by these antibodies decrease and the lacto‐series glycolipids, reacting with the SSEA‐1 antibody appear. This antigenic conversion suggests that a shift of glycolipid synthesis from globo‐series to lacto‐series glycolipids occurs during differentiation of human teratocarcinoma and perhaps of pre‐implantation mouse embryos.

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The selective emigration of blood born leukocytes into tissues is mediated. in part by interactions of Ig-like cell adhesion molecules (IgCAMs) expressed on vascular endothelium and their cognate ligands. thc lcukocyte integrins. Within niucosal lymphoid tissues and gastrointestinal sites the inucosai vascular addressin. MAdCAM-I is the predominant IgCAM. mediating specific lymphocyte homing via interactions with its ligand on lymphocytes, the integrin 04/17. Previous studies have shown thal an essential binding motif resides in the first Ig domain of all IgCAMs, containing an acidic residue ( D or E) preceded by an aliphatic residue ( L or I ) that resides in strand C or the C D loop. However, domain swap experiments with MAdCAM-I and VCAM-I havc shown a requirement for both Igdoinains 1 and 2 for efficient integrin binding. Wedescribe the use of chimeric MAdCAM-I/VCAM-I receptors and point mutations in MAdCAM-I to define other sites that are required for binding t o the integrin (u4;j7. Wc find that, in addition to critical C D loop residues, other regions in both domain one and two contribute to MAdCAM-I /a407 interactions. including a buried arginine residue in the F strand of domain one and several acidic residues in a highly extended DE ribbon in domain 2. These mutations, when placed in the recently solved crystal structure of human MAdCAM-I give insight into the integrin binding preference of this unique receptor. Ki,iiiorrl\ MAdCAM-1, VCAM-I. ICAM-I. IgCAM, mAb, MEM. FCS Ahhwiitr/iolr.\. MAdCAM-I. Mucosnl addressin cell adhesion molecule-I: VCAM-I. Vasculnr cell adhesion molecule-I: ICAM-I. IgCAM. Imniunoglobulin like cell adhehion molecules: niAb. monoclonal antibody: MEM. minimal essential media; FCS, fetal calf SCI uill