The B lymphocyte adhesion molecule CD22 interacts with leukocyte common antigen CD45RO on T cells and alpha 2-6 sialyltransferase, CD75, on B cells

Cell surface beta 1,4-galactosyltransferase functions during neural crest cell migration and neurulation in vivo

Mesenchymal cell migration and neurite outgrowth are mediated in part by binding of cell surface beta 1,4-galactosyltransferase (GalTase) to N-linked oligosaccharides within the E8 domain of laminin. In this study, we determined whether cell surface GalTase functions during neural crest cell migration and neural development in vivo using antibodies raised against affinity-purified chicken serum GalTase. The antibodies specifically recognized two embryonic proteins of 77 and 67 kD, both of which express GalTase activity. The antibodies also immunoprecipitated and inhibited chick embryo GalTase activity, and inhibited neural crest cell migration on laminin matrices in vitro. Anti-GalTase antibodies were microinjected into the head mesenchyme of stage 7-9 chick embryos or cranial to Henson's node of stage 6 embryos. Anti-avian GalTase IgG decreased cranial neural crest cell migration on the injected side but did not cross the embryonic midline and did not affect neural crest cell migration on the uninjected side. Anti-avian GalTase Fab crossed the embryonic midline and perturbed cranial neural crest cell migration throughout the head. Neural fold elevation and neural tube closure were also disrupted by Fab fragments. Cell surface GalTase was localized to migrating neural crest cells and to the basal surfaces of neural epithelia by indirect immunofluorescence, whereas GalTase was undetectable on neural crest cells prior to migration. These results suggest that, during early embryogenesis, cell surface GalTase participates during neural crest cell migration, perhaps by interacting with laminin, a major component of the basal lamina. Cell surface GalTase also appears to play a role in neural tube formation, possibly by mediating neural epithelial adhesion to the underlying basal lamina.

Recombinant globulins: novel research tools and possible pharmaceuticals

A novel approach to the study of proteins is the construction of chimeras consisting of a target protein fused to an immunoglobulin constant domain. These recombinant globulins have been used in the identification of ligand-receptor pairs, determination of functional consequences of receptor engagement, the elucidation of structural domains necessary for ligand binding, and as potential therapeutic agents.

Maturation and dispersal of B-cell clones during T cell-dependent antibody responses

Germinal centers develop in follicles during TD antibody responses in the first 3 wk following each immunization. In primary responses to protein-based antigens, T-cell help is limiting, follicles develop towards the end of the 1st wk from immunization and the size of the follicular response in relatively small. When T-cell help is provided the primary B-cell response in follicles is much larger, B cells start to proliferate in follicles within a few hours of immunization and reach peak size 3-4 d later. Available evidence suggests that virgin B cells that colonize follicles to form germinal centers must first be activated by antigen outside follicles, probably in T zones. Memory B cells also proliferate in follicles and they can do so without first being activated outside follicles. Germinal center formation consists of an initial phase of exponential proliferation of B cells within the follicular dendritic cell network. After a single immunization the follicular response is oligoclonal and on average only 3 cells colonize each follicle. In responses to hapten-protein in rats primed previously with the carrier protein these 3 cells increase to around 10(4) cells in 3 d with a cell cycle time of about 6 h. At the end of the period of exponential growth of B blasts, the classical structure of germinal centers emerges. The B blasts become centroblasts in the dark zone of the germinal center which develops at that pole of the FDC network nearer the T zones. The centroblasts are still in rapid cell cycle but do not more than sustain their numbers. The rest of their progeny move to the heart of the FDC network where they come out of cell cycle as centrocytes. Evidence is cited which indicates that somatic mutation occurs in the Ig V-region genes of centroblasts and that centrocytes are selected on the basis of their ability to respond to antigen held on FDC. Centrocytes not receiving this antigen-dependent signal kill themselves by apoptosis. Centrocytes positively selected by interaction with antigen on FDC receive further signals which induce the cells to differentiate to become either plasma cells or memory B cells. The nature of some of these differentiation signals is described. It is shown that proliferation, selection and differentiation occur within germinal centers in distinct micro-environments.(ABSTRACT TRUNCATED AT 400 WORDS)

Selectins and other mammalian sialic acid-binding lectins

Several recently discovered mammalian cell adhesion proteins recognize and bind to sialic acid-containing ligands. Reports concerning the molecular specificities of these interactions have been intriguing but somewhat confusing, partly because of pitfalls in methodology or interpretation. Nevertheless, these protein-carbohydrate recognition phenomena are important in the normal biology of blood cells and in the pathophysiology of many diseases.

Macaque CD4+ T-cell subsets: influence of activation on infection by simian immunodeficiency viruses (SIV)

Simian immunodeficiency virus (SIV) infects a small number of CD4+ T cells including "memory" T cells. The following describes the cell surface markers which may delineate subsets of CD4+ memory T cells and reviews how memory CD4+ T cells are activated and regulated through the T-cell receptor and such accessory receptors as CD28. The factors which may influence initial expression and infection of T cells by CD4 are discussed. Unlike activated and infected T cells, unstimulated CD4+ T cells have little or no SIV DNA detectable in the genomic fraction, but key activation signals may promote integration of viral DNA in memory T cells. Bacterial superantigens (SuperAg) can promote increased levels of SIV viral DNA in mature and immature T cells. Immunodeficiency virus products such as gp120, Nef, and Tat can affect CD4+ T-cell function. Whereas Nef can reduce expression of CD4, Tat reduces the expression of CD28. We hypothesize that the lack of expression of key accessory molecules on CD4 lineage T cells infected with immunodeficiency viruses may make infected T cells more susceptible to recall-antigen-induced programmed cell death.