William W. Young

The distribution of blood group antigens in rodent epithelia

SummaryThe pattern of distribution of antigens cross-reacting with antibodies to human blood group antigens A and B and two precursor molecules was examined by immunofluorescence in the epidermis, oral mucosa and forestomach of rats and mice. Staining for blood group antigen A was negative. In all epithelia examined, blood group antigen B was present at the surface of basal and parabasal cells, and the H antigen at the surface of spinous cells. N-acetyllactosamine was present on the cell membranes in the upper spinous and granular cell layers of epidermis and forestomach epithelium and was not expressed in the oral epithelia except for a limited area in the dorsal tongue epithelium.Thus, the expression of antigen varies both regionally and, as earlier shown in human epithelium, with the stage of maturation of cells within a given epithelium. The observed sequence of expression of these antigens during maturation differs from that of human epithelia, but the present study provides a basis for further experimental studies of the role of cell surface antigens in epithelial homeostasis and maturation.

Polarity of the Forssman glycolipid in MDCK epithelial cells.

To determine whether epithelial plasma membrane glycolipids are polarized in a manner analogous to membrane proteins, MDCK cells grown on permeable filters were analyzed for the expression of Forssman ceramide pentasaccharide, the major neutral glycolipid in these cells. In contrast to a recent report which described exclusive apical localization of the Forssman glycolipid (Hansson, G.C., Simons, K. and Van Meer, G. (1986) EMBO J. 5, 483-489), immunofluorescence and immunoelectron microscopic staining revealed the Forssman glycolipid on both the apical and basolateral surfaces of polarized cells. Immunoblots indicated that the Forssman antigen was detectable only on glycolipids and not on proteins. Analysis of metabolically labeled glycolipids released into the apical and basal culture medium, either as shed membrane vesicles or in budding viruses, also demonstrated the presence of the Forssman glycolipid on both apical and basolateral membranes of polarized cells. Quantitation of the released glycolipid indicated that the Forssman glycolipid was concentrated in the apical membrane. These results are consistent with previous reports which described quantitative enrichment of glycolipids in the apical domain of several epithelia.

Molecular Organization of Glycosphingolipids in Phosphatidylcholine Bilayers and Biological Membranes

Glycosphingolipids, in contrast to glycerol-based lipids, are relatively minor components of mammalian cell membranes. They are, however, confined to the external surface of the plasma membrane and in this surface may collectively be a major component (1–4). In some cell types very small amounts of these lipids have been found associated with Golgi membranes, their probable site of biosynthesis (1). Their location on the trans-cytoplasmic side of the plasma membrane causes them, together with glycosylated membrane proteins, to be the primary components of the cell to interact with the molecules and other cells of the immediate environment. Thus specific glycosphingolipids have been shown to serve as receptors for toxins, viruses and some hormones (2,5–11). They have long been known to act as antigenic determinants and to mediate immune responses (11–13). There is much evidence to suggest that glycosphingolipids play a role in cell-cell interaction and recognition (7). Alterations in the amounts and types of these lipids on the cell surface are very often associated with growth, differentiation, development, aging (7,14,15), and with oncogenic transformation (11,16). Although there is considerable information about the molecular structure of many glycosphingolipids, relatively little is known about the organization of molecules of this class in phospholipid bilayers and in the bilayers of biological membranes. It seems certain that their molecular organization is a critical parameter underlying many of the functions of glycosphingolipids (17).

Crystal structure of an anti-Lewis a Fab determined by molecular replacement methods

The anti-Lewis alpha mouse immunoglobulin CF4C4 (IgGl, k) Fab has been crystallized from 58% saturated ammonium sulfate in space group Pl; unit cell dimensions a = 43.4 A b = 41.7 A, c = 62.0 A, a = 72.7 degrees, beta = 96.6 degrees, gamma = 100.1 degrees. X-ray diffraction data have been measured beyond 3.0 A Bragg spacing. The crystal structure has been determined by molecular replacement methods, using as search models the constant and variable domains of the mouse immunoglobulin McPC603 (IgA, kappa) Fab. The crystallographic residual for the data 5.0 to 4.0 A, is 0.47. The approximate 2-fold axis relating the VL and the VH domains forms an angle of 164 degrees with the 2-fold axis relating the constant domains. The crystal packing is reasonable.