Analysis of structural similarities between brain Thy-1 antigen and immunoglobulin domains. Evidence for an evolutionary relationship and a hypothesis for its functional significance

A year in the life of the immunoglobulin superfamily

The superfamily of molecules with immunoglobulin-like domains has recently been gaining new members-largely on the basis of sequence homology. Here Alan Williams reviews this new work and reveals how the comparison of sequence patterns enables decisions on membership to be made. Accommodation of the new structures demands the provision of new categories, and forces the abandonment of the conserved disulphide bond as the last invariant characteristic of an immunoglobulin-type domain. They may, however, provide more dues to the origins and evolution of the immunoglobulin superfamily.

Immune maintenance of self in morphostasis of distinct tissues, tumour growth and regenerative medicine

Morphostasis (tissue homeostasis) is a complex process consisting of three circumstances: (1) tissue renewal from stem cells, (2) preservation of tissue cells in a proper differentiated state and (3) maintenance of tissue quantity. This can be executed by a tissue control system (TCS) consisting of vascular pericytes, immune system-related components--monocyte-derived cells (MDC), T cells and immunoglobulins and autonomic innervation. Morphostasis is established epigenetically, during the critical developmental period corresponding to the morphogenetic immune adaptation. Subsequently, the tissues are maintained in a state of differentiation reached during the adaptation by a 'stop effect' of MDC influencing markers of differentiating tissue cells and presenting self-antigens to T cells. Retardation or acceleration of certain tissue differentiation during adaptation results in its persistent functional immaturity or premature ageing. The tissues being absent during adaptation, like ovarian corpus luteum, are handled as a 'graft.' Morphostasis is altered with age advancement, because of the degenerative changes of the immune system. That is why the ageing of individuals and increased incidence of neoplasia and degenerative diseases occur. Hybridization of tumour stem cells with normal tissue cells causes an augmentation of neoplasia by host pericytes and MDC stimulating a 'regeneration' of depleted functional cells. Degenerative diseases are associated with apoptosis. If we are able to change morphostasis in particular tissue, we may disrupt apoptotic process of the cell. An ability to manage the 'stop effect' of MDC may provide treatment for early post-natal tissue disorders, improve regenerative medicine and delay physical, mental and hormonal ageing.

Immune physiology in tissue regeneration and aging, tumor growth, and regenerative medicine

The immune system plays an important role in immunity (immune surveillance), but also in the regulation of tissue homeostasis (immune physiology). Lessons from the female reproductive tract indicate that immune system related cells, such as intraepithelial T cells and monocyte-derived cells (MDC) in stratified epithelium, interact amongst themselves and degenerate whereas epithelial cells proliferate and differentiate. In adult ovaries, MDC and T cells are present during oocyte renewal from ovarian stem cells. Activated MDC are also associated with follicular development and atresia, and corpus luteum differentiation. Corpus luteum demise resembles rejection of a graft since it is attended by a massive influx of MDC and T cells resulting in parenchymal and vascular regression. Vascular pericytes play important roles in immune physiology, and their activities (including secretion of the Thy-1 differentiation protein) can be regulated by vascular autonomic innervation. In tumors, MDC regulate proliferation of neoplastic cells and angiogenesis. Tumor infiltrating T cells die among malignant cells. Alterations of immune physiology can result in pathology, such as autoimmune, metabolic, and degenerative diseases, but also in infertility and intrauterine growth retardation, fetal morbidity and mortality. Animal experiments indicate that modification of tissue differentiation (retardation or acceleration) during immune adaptation can cause malfunction (persistent immaturity or premature aging) of such tissue during adulthood. Thus successful stem cell therapy will depend on immune physiology in targeted tissues. From this point of view, regenerative medicine is more likely to be successful in acute rather than chronic tissue disorders.

Oogenesis in adult mammals, including humans: a review

The origin of oocytes and primary follicles in ovaries of adult mammalian females has been a matter of dispute for over 100 yr. The prevailing belief that all oocytes in adult mammalian females must persist from the fetal period of life seems to be a uniquely retrogressive reproductive mechanism requiring humans to preserve their gametes from the fetal period for several decades. The utilization of modern techniques during last 10 yr clearly demonstrates that mammalian primordial germ cells originate from somatic cell precursors. This indicates that if somatic cells are precursors of germ cells, then somatic mutations can be passed on to progeny. Mitotically active germline stem cells have been described earlier in ovaries of adult prosimian primates and recently have been reported to also be present in the ovaries of adult mice. We have earlier shown that in adult human females, mesenchymal cells in the ovarian tunica albuginea undergo a mesenchymal-epithelial transition into ovarian surface epithelium cells, which differentiate sequentially into primitive granulosa and germ cells. Recently, we have reported that these structures assemble in the deeper ovarian cortex and form new follicles to replace earlier primary follicles undergoing atresia (follicular renewal). Our current observations also indicate that follicular renewal exists in rat ovaries, and human oocytes can differentiate from ovarian surface epithelium in fetal ovaries in vivo and from adult ovaries in vitro. These reports challenge the established dogma regarding the fetal origin of eggs and primary follicles in adult mammalian ovaries. Our data indicate that the pool of primary follicles in adult human ovaries does not represent a static but a dynamic population of differentiating and regressing structures. Yet, the follicular renewal may cease at a certain age, and this may predetermine the onset of the natural menopause or premature ovarian failure. A lack of follicular renewal in aging ovaries may cause an accumulation of spontaneously arising or environmentally induced genetic alterations of oocytes, and that may be why aging females have a much higher chance of having oocytes with more mutations in persisting primary follicles.

Expression, purification, and characterization of avian Thy-1 from Lec1 mammalian and Tn5 insect cells

Structural studies of asparagine-linked glycoproteins are complicated by the oligosaccharide heterogeneity inherent to individual glycosylation sites. Herein, we report the cloning of a novel isoform of avian Thy-1 and the subsequent expression, purification, and characterization of a soluble form of Thy-1 from Lec1 mammalian and Tn5 insect cells. The novel isoform of Thy-1 differs from the previously reported chicken isoform by eight amino acid residues, but these changes do not alter the secondary structure content, the disulfide bond pattern, or the sites of glycosylation. The disulfide linkage pattern and glycoform distribution on each N-glycosylation site of recombinant chicken Thy-1 from both cell lines were determined by a combination of amino-terminal sequencing and mass spectrometry. The mass spectral data showed that the amino-terminal glutamine was modified to pyroglutamate. Recombinant Thy-1 from Lec1 cells contained (GlcNAc)(2)(Man)(5) on asparagine 60, whereas the oligosaccharides on asparagine 23 and 100 contained approximately 80% (GlcNAc)(2)(Man)(4) and approximately 20% (GlcNAc)(2)(Man)(5). The glycoforms on Thy-1 expressed in Tn5 cells were more heterogeneous, with the oligosaccharides ranging over (GlcNAc)(2)(Fuc)(0-2)(Man)(2-3) on each site. The ability to generate recombinant glycoproteins with restricted carbohydrate heterogeneity is the first step toward the systematic study of structure-function relationships in intact glycoproteins.

Association of mesenchymal cells and immunoglobulins with differentiating epithelial cells

BACKGROUND

Mesenchymal-epithelial interactions play an important role in the physiology and pathology of epithelial tissues. Mesenchymal cells either associate with epithelium basement membrane [pericytes and perivascular monocyte-derived cells (MDC)] or reside within epithelium (MDC and T cells). Although intraepithelial mesenchymal cells were suggested to contribute to the epithelium physiology, their association with particular steps in differentiation of epithelial cells, interactions among themselves, and their fate remain unclear. We studied epitopes of mesenchymal cells and their products (immunoglobulins) in stratified epithelium of uterine ectocervix, which is one of the prototypes of complete cellular differentiation from stem into the aged cells.

RESULTS

Perivascular CD14 primitive MDC associated with basal (stem) epithelial cells. Thy-1 pericytes of microvasculature secreted intercellular vesicles, which associated with Ki67 postmitotic epithelial cells expressing MHC class I. Intraepithelial T cells showed an association with veiled type MDC [dendritic cell (DC) precursors] among parabasal cells, and exhibited fragmentation after entering intermediate (mature) epithelial layers. Mature DC secreted CD68 and exhibited fragmentation after reaching mid intermediate layers. Binding of IgM was detected at the top of each layer: in the upper parabasal, upper intermediate, and most surface epithelial cells. IgG was confined to the entire superficial layer.

CONCLUSIONS

These data suggest that the phylogenetically and ontogenetically developed hierarchy of mesenchymal cells (MDC, pericytes, T cells) and immunoglobulins (IgM, IgG) accompanies differentiation of epithelial cells from immature into the mature and aged phenotype. Further studies of an involvement of mesenchymal cells in the regulation of tissue homeostasis may bring novel approaches to the prevention and therapy of tissue dysfunctions characterized by permanent tissue immaturity (muscular dystrophy) or accelerated aging (degenerative diseases).

Thy-1 differentiation protein and monocyte-derived cells during regeneration and aging of human placental villi

PROBLEM

The classification of placental villi was reviewed, and regeneration of villous trees in mature human placentae was examined.

METHOD OF STUDY

Expression of Thy-1 by placental fibroblasts and pericytes, and markers of endothelial cells and monocyte-derived cells were studied by immunohistochemistry and image analysis.

RESULTS

Villous regeneration consists of: (i) dedifferentiation of mature ramuli into young stem villi producing mesenchymal villi; (ii) differentiation of mesenchymal villi into immature intermediate villi; and (iii) differentiation of immature intermediate villi into transitory intermediate villi, branching into the precursors of mature intermediate and terminal villi. These processes are associated with dedifferentiation and redifferentiation of placental monocyte-derived cells. Significant changes of Thy-1 expression by fibroblasts and pericytes accompany aging and degeneration, as well as regeneration of placental villi.

CONCLUSIONS

Villous aging and degeneration in normal mature human placenta is compensated by regeneration of villous trees. Lack of villous regeneration may cause chronic fetal distress, due to the increasing demands of the growing fetus on the remaining terminal villi.

Differential expression of platelet-derived growth factor-alpha receptor by Thy-1(-) and Thy-1(+) lung fibroblasts

Fibroblasts are heterogeneous with respect to surface markers, morphology, and participation in fibrotic responses. This study was undertaken to determine whether Thy-1(-) and Thy-1(+) rat lung fibroblasts, which have distinct and relevant phenotypes, differ in their proliferative responses to platelet-derived growth factor (PDGF) isoforms. Homogeneous populations of Thy-1(-) and Thy-1(+) fibroblasts were found to proliferate equally in the presence of PDGF-BB, but PDGF-AA-mediated proliferation occurred only in Thy-1(-) cells. This differential activity correlated with significantly higher expression of PDGF-alpha receptor in Thy-1(-) fibroblasts as shown by immunoblotting, immunofluorescence, and Northern blotting. There was a rapid increase in c-myc mRNA in Thy-1(-) but not in Thy-1(+) fibroblasts on stimulation with PDGF-AA and PDGF-BB. The PDGF-alpha receptor, which mediates signaling by all PDGF isoforms, has been implicated in numerous clinical and experimental forms of fibrosis and regulates lung morphogenesis. Differential expression of the PDGF-alpha receptor supports distinct roles for Thy-1(-) and Thy-1(+) fibroblast populations in developmental and fibrotic processes in the lung.

Thy-1 is a component common to multiple populations of synaptic vesicles

Thy-1, a glycosylphosphatidylinositol-linked integral membrane protein of the immunoglobulin superfamily, is a component of both large dense-core and small clear vesicles in PC12 cells. A majority of this protein, formerly recognized only on the plasma membrane of neurons, is localized to regulated secretory vesicles. Thy-1 is also present in synaptic vesicles in rat central nervous system. Experiments on permeabilized PC12 cells demonstrate that antibodies against Thy-1 inhibit the regulated release of neurotransmitter; this inhibition appears to be independent of any effect on the Ca2+ channel. These findings suggest Thy-1 is an integral component of many types of regulated secretory vesicles, and plays an important role in the regulated vesicular release of neurotransmitter at the synapse.

Thy-1 immunoreactivity in the larval sea lamprey (Petromyzon marinus L.), a vertebrate without a definitive thymus

Agnathans are the only vertebrates without a thymus, yet lampreys possess putative lymphocytes whose responses parallel those of T cells in gnathostomes. The phylogenetically conserved Thy-1 antigen is often associated with the thymus, thymocytes, and T cells. An immunohistochemical study, using commercial anti-rat brain Thy-1.1 antiserum and an immunoperoxidase procedure (peroxidase anti-peroxidase) was conducted to identify any Thy-1 antigenicity in various tissues of larval sea lampreys (Petromyzon marinus L.) lightly fixed in a chilled aldehyde-based solution. The primary focus of the experiment was to discover if Thy-1 immunoreactivity was associated with haemopoietic sites and (or) leukocytes. This technique permitted conventional histological sectioning, preserved tissue architecture, and retained Thy-1 antigenicity. In the haemopoietic typhlosole, the peripheral stroma and many lymphocyte-like cells stained intensely, as did similar cells in the opisthonephros, intestinal venous sinus, and liver. Immunoreactivity in the pharynx was evidenced only by weakly staining stroma in small labyrinthine subdermal foci dorsal and ventral to some external gill openings. It is proposed that if functions analogous to thymic activities exist in the larval lamprey, the typhlosole is the most likely site for their discovery.

Molecular cloning and primary structure of the avian Thy-1 glycoprotein

We have previously characterised, both biochemically and immunohistochemically, a 23 kDa putative avian Thy-1 protein homologue. In this report we have examined the carbohydrates present on the protein and determined the partial protein sequence of enzymatically and CNBr-produced peptides. The protein sequences enabled us to clone an essentially full-length (1854 bp) cDNA using PCR and colony screening of an embryonic day (ED) 18 forebrain pUEX-1 cDNA library. Analysis of deduced amino acid sequence shows the 23 kDa protein to be 110 amino acids in length compared to mouse (112) and human and rat (111) while still retaining the conserved cysteine residues. The N-glycosylation site at position 61 is the same as that in the human protein, but is different from that in the rodent (position 75). Northern blot analysis of Thy-1 mRNA expression in the forebrain, cerebellum and tectum show that all three tissues have low levels at ED4 (forebrain and tectum) and ED8 (cerebellum), rising most rapidly between ED16 and the first few days post-hatch. Analysis of various tissues at hatch and adult show expression to be predominantly neuronal with very low levels in some other organs, mainly at hatch, indicating the possibility of subsets of cells, which we have also seen in histological sections, in these tissues expressing Thy-1 mRNA. Bone marrow and blood cells were also negative for Thy-1 protein.

Cell-mediated and neural control of morphostasis

Morphostasis refers to the maintenance of the differentiated state of tissues in an adult individual and it represents a basal event of homeostasis and the organism's existence. Most of the cells in the body are arrested in their differentiation at a certain point related to their optimal function. Evidence is rapidly accumulating on the general role of immunoglobulin-gene superfamily (IGSF) domains in the non-immune control of behavior of cells in various tissues. A novel 'tissue control system' (TCS) has been suggested, supporting the differentiation of tissue cells in an adult organism and functioning via the IGSF domains and cell-mediated control of morphostasis. We assume here that the morphostasis is established epigenetically during the early adaptive period. With its termination, coinciding with the attainment of an organism's immunocompetence, the combination of cell surface markers of the most mature cells in tissues are encoded in the TCS as the stop-signal (SS). This stage of tissue differentiation is maintained during further life: upon recognition of SS the committed TCS element does not stimulate further differentiation of the cell, i.e. it exhibits a stop-effect (SE). Each tissue-specific cell line has only one or no SE established depending on its presence or absence during development, respectively. The only way to escape an established SE and continue in differentiation is to change at least a portion of the SS. Hormones might act here directly, by conformation of their cell surface receptors recognized as a portion of SS, or indirectly, by influencing proteosynthesis of cell surface markers.(ABSTRACT TRUNCATED AT 250 WORDS)

A simple method to generate non-trivial alternate alignments of protein sequences

A major problem in sequence alignments based on the standard dynamic programming method is that the optimal path does not necessarily yield the best equivalencing of residues assessed by structural or functional criteria. An algorithm is presented that finds suboptimal alignments of protein sequences by a simple modification to the standard dynamic programming method. The standard pairwise weight matrix elements are modified in order to penalize, but not eliminate, the equivalencing of residues obtained from previous alignments. The algorithm thereby yields a limited set of alternate alignments that can differ considerably from the optimal. The approach is benchmarked on the alignments of immunoglobulin domains. Without a prior knowledge of the optimal choice of gap penalty, one of the suboptimal alignments is shown to be more accurate than the optimal.

Brain-associated glycoproteins expressed in bovine heart Purkinje fibres

The Purkinje fibres of bovine heart were investigated immunohistochemically by use of monoclonal antibodies with specificity against the glycoproteins Thy-1 and Gp120, expressed in human brain. The existence and expression in bovine tissues (brain and thymus) of antigens displaying similar properties and immunochemical crossreactivity with monoclonal antibodies against the human antigens were confirmed. Both these antigens, as identified by use of anti Thy-1 and anti-Gp120 monoclonal antibodies were found to be associated with the membranes of the impulse conduction system. The presence of the antigens was seen in areas facing other conduction cells. No parts of the cells facing the basal membrane of the fibres were stained. The continuous staining between the cells was different from that of desmosome related proteins. These findings may have physiological and functional implications and are interesting in relation to recent evidences suggesting that the conduction tissue might be a derivative of the neural crest.

Structural design and molecular evolution of a cytokine receptor superfamily

A family of cytokine receptors comprising molecules specific for a diverse group of hematopoietic factors and growth hormones has been principally defined by a striking homology of binding domains. This work proposes that the approximately 200-residue binding segment of the canonical cytokine receptor is composed of two discrete folding domains that share a significant sequence and structural resemblance. Analogous motifs are found in tandem approximately 100-amino acid domains in the extracellular segments of a receptor family formed by the interferon-alpha/beta and -gamma receptors and tissue factor, a membrane tether for a coagulation protease. Domains from the receptor supergroup reveal clear evolutionary links to fibronectin type III structures, approximately 90-amino acid modules that are typically found in cell surface molecules with adhesive functions. Predictive structural analysis of the shared receptor and fibronectin domains locates seven beta-strands in conserved regions of the chain; these strands are modeled to fold into antiparallel beta-sandwiches with a topology that is similar to immunoglobulin constant domains. These findings have strong implications for understanding the evolutionary emergence of an important class of regulatory molecules from primitive adhesive modules. In addition, the resulting double-barrel design of the receptors and the spatial clustering of conserved residues suggest a likely binding site for cytokine ligands.

Regulation of murine B cell Thy-1 expression by IL-4, IFN-gamma, and CD4+ T cell subsets

Interleukin 4 (IL-4) induces the expression of membrane Thy-1 on the vast majority of lipopolysaccharide (LPS)-stimulated normal murine B cells in vitro. This induction is inhibited by interferon-gamma (IFN-gamma). IL-4 and IFN-gamma are required late in culture to effect maximal induction and inhibition of Thy-1 expression by LPS- or LPS + IL-4-stimulated B cells, respectively. IFN-gamma suppresses IL-4-induced Thy-1 expression by inhibiting the induction of steady-state levels of Thy-1-specific mRNA. Three distinct CD4+ Th2 clones, through their release of IL-4, induce B cells to express high levels of Thy-1, by 24 hr, in striking contrast to the 3 days required to induce Thy-1 expression after stimulation with LPS and IL-4. This induction is abrogated by the addition of IFN-gamma. B cells stimulated with three distinct Th1 clones (IFN-gamma- and IL-2-producing) exhibit a modest, non-IL-4-dependent, expression of Thy-1. In contrast to intrinsic expression of Thy-1 by Th2-stimulated B cells. Thy-1 expressed by Th1-stimulated B cells is acquired, having the allotype specificity of the stimulating T cell.

Gene targeting at the human CD4 locus by epitope addition

Homologous recombination at the CD4 locus in a human T-cell line has been achieved by an approach called epitope addition. The endogenous CD4 gene provided transcription, translation, and leader sequences to a crippled introduced Thy-1 gene, resulting in the expression of murine Thy-1 epitopes on the surface of the human cells. Thy-1+ cells were selected using the Fluorescence Activated Cell Sorter (FACS). An estimated 700-fold enrichment for homologous versus nonhomologous integration events was obtained, such that 70% of cells scoring positive for Thy-1 were derived from gene targeting. Three of the Thy-1+ cell lines expressed protein only from the targeted allele; thus, these cells were functionally CD4-.

Evidence from neuron/lymphoma heterokaryons for a common trans-acting factor suppressing Thy-1 expression

We have investigated the tissue specificity of a trans-acting regulatory factor observed to suppress Thy-1 expression during normal neuronal differentiation. Heterokaryons were constructed between Thy-1.1+ expressing mouse T cell lymphoma cells and Thy-1.2- mouse sensory neurons and their surface phenotypes determined by immunofluorescence histochemistry 16 h after fusion. Thy-1.1 expression was observed to be specifically suppressed in such heterokaryons whilst the expression of the lymphoma cell surface marker, Ly-1, was not altered. As the nuclei did not fuse in the heterokaryons, it appears that the developmentally regulated diffusible suppressor factor active in sensory neurons is not tissue specific and can down-regulate Thy-1 expression in lymphoma cells. We also report the suppression of the H-2Kk surface antigen in heterokaryons by a similar but independent regulatory mechanism.

NCAM and Thy-1 in special sense organs of the developing mouse

The distribution of the neural cell adhesion molecule (NCAM) and Thy-1 in the olfactory mucosa and olfactory bulb, the eye and the inner ear was examined with immunocytochemistry in mouse embryos from embryonic day 12 (E 12) to embryonic day 19 (E 19). In general, neurons are completely outlined with NCAM, whereas Thy-1 outlines only dendrites and axons. A variable cytoplasmic staining for Thy-1 is present in the perikarya. Neurons directly associated with special sense organs express NCAM and Thy-1 already from the earliest stage and throughout the period investigated, apart from the olfactory neurons in which Thy-1 disappears at E 19. The mitral cells in the olfactory bulb show Thy-1 but no NCAM reactivity. In the eye, lens fibers express Thy-1 and the pigmented layer expresses NCAM; neither of the two molecules can be detected at E 19. In the inner ear, hair cells express NCAM at E 19. Based on the distribution during the developmental period studied and on the cellular localisation of reaction products, it is suggested that the NCAM adhesion function could be of a more general nature by keeping appropriate cell membranes in close contact and thereby allowing more specific molecular interactions to take place. Thy-1, which is located on dendrites and axons, could be such a specific factor and function as recognition molecule in the developing nervous system.

Histological and immunohistological analysis of human lymphomas

Morphological and immunological characteristics of lymphoproliferative diseases are reviewed. In particular, a basic distinction is made between non-Hodgkin's lymphomas and Hodgkin's disease. As to the non-Hodgkin's lymphomas, emphasis is given to the problems of classification, technical approach, histogenesis, and prognosis. The authors adopt a version of the Kiel Classification modified to take account of new knowledge regarding T-cell lymphomas. The value of immunophenotyping in making an accurate distinction between the various categories is stressed; immunocytochemical detection of the growth fraction is also discussed and then proposed as a new prognostic tool. Finally, the criteria for differential diagnosis between non-Hodgkin's lymphomas, malignant histiocytosis, non-lymphoid large cell tumors, and atypical immune reactions are outlined.

Thy-1-mediated regulation of a low-threshold transient calcium current in cultured sensory neurons

The physiological effect of ligand binding to the Thy-1 molecule expressed on the neuronal cell surface was examined. Sensory neurons obtained from dorsal root ganglia of 2-day-old CBA/CAH mice (Thy-1.2) were cultured in vitro for 8 days, and then patch-clamp recordings were obtained of calcium currents. It was found that binding of an anti-Thy-1.2 monoclonal antibody to neurons expressing the Thy-1.2 moiety increased the amplitude of a low-threshold transient calcium current. Monoclonal antibodies directed against the Thy-1.1 molecule or a neuronal surface ganglioside (A2B5) had no effect on this calcium current in Thy-1.2-bearing cells, nor did they interfere with subsequent activation by the anti-Thy-1.2 monoclonal antibody. These results demonstrate that ligand binding to the Thy-1 molecule transduces a physiological signal in sensory neurons by increasing a voltage-activated calcium current.

Squid glycoproteins with structural similarities to Thy-1 and Ly-6 antigens

In an attempt to identify invertebrate homologs of Thy-1 antigen, the optic and central nervous tissue of squid was solubilized in deoxycholate and fractionated by lentil lectin affinity chromatography and gel filtration to yield small abundant glycoproteins. Material with biochemical similarities to Thy-1 was found and shown to consist of two glycoproteins that were ultimately purified using monoclonal antibody affinity columns. Both glycoproteins were sequenced to yield sequences of 84 residues for Sgp-1 and 92 residues for Sgp-2. The sequences were analyzed for similarities to Thy-1 and other Ig-related sequences, and Sgp-1 showed some similarities that were greater than 3 standard deviation units away from mean random scores when tested with the ALIGN program. However, the sequence patterns were not typical of Ig-related domains and the relationship of Sgp-1 to the Ig superfamily remains problematical. Sgp-2 showed no relationship to the Ig superfamily, but similarities to Ly-6 antigen sequences were noted that are in accord with an evolutionary relationship. The similarities included ten Cys residues in each sequence of which eight were matched in the best alignment given by the ALIGN program. Chemical evidence was obtained for glycophospholipid tails at the COOH-termini of Sgp-1 and Sgp-2 as is the case for Thy-1 and Ly-6 antigens.

Differential expression of class II major histocompatibility complex and Thy 1.2 antigens on mouse decidua

A differential expression of class II major histocompatibility complex (MHC) and Thy 1.2 antigens was detected on two morphologically distinct cell populations in short-term cultures of murine decidual tissue. Stromal type decidual cells expressed Thy 1.2, albeit transiently, and consistently lacked class II antigens. By contrast decidual macrophages expressed class II antigens and lacked Thy 1.2 antigens. Stromal type decidual cells, after culture in the presence of indomethacin, displayed no evidence of prostaglandin-mediated modulation of class II expression. These findings suggest that class II positive decidual macrophages are responsible for the antigen-presenting capacity of decidua.

L3T4 and the immunoglobulin gene superfamily: new relationships between the immune system and the nervous system

L3T4 is a mouse cell surface protein expressed on most thymocytes and on the subset of mature T cells that recognizes class II MHC molecules. Its primary function on T cells is most likely that of increasing the avidity of the interaction between T cells and antigen-presenting or target cells. It may accomplish this by binding to a nonpolymorphic region on class II MHC molecules. The cDNA and gene encoding L3T4 have been isolated and sequenced. Analysis of the amino acid sequence predicted by the nucleotide sequence indicates that L3T4 is a member of the Ig gene superfamily. It is most closely related to Ig and Tcr V regions. Although the amino-terminal domain of L3T4 is the portion of the molecule that is most similar to V-regions, L3T4 is one of the polydomain members of the Ig gene superfamily. Studies of the expression of L3T4 mRNA in various tissues led to the surprising finding that this gene is transcribed not only in T lymphoid cells, but also in brain. The predominant form of L3T4 mRNA expressed in brain is foreshortened as compared to that in T lineage cells, and it is most likely the product of a distinct transcriptional start site. If translated, the protein encoded by this brain transcript would be 217 amino acids in length and would lack the signal peptide and the amino-terminal 214 amino acids of the mature protein. It is not known whether a stable protein product is synthesized from this mRNA or what its function might be. However, these findings place L3T4 in an intriguing class of Ig gene superfamily members characterized by coexpression in the immune system and the nervous system.

A strategy for the rapid multiple alignment of protein sequences. Confidence levels from tertiary structure comparisons

An algorithm is presented for the multiple alignment of protein sequences that is both accurate and rapid computationally. The approach is based on the conventional dynamic-programming method of pairwise alignment. Initially, two sequences are aligned, then the third sequence is aligned against the alignment of both sequences one and two. Similarly, the fourth sequence is aligned against one, two and three. This is repeated until all sequences have been aligned. Iteration is then performed to yield a final alignment. The accuracy of sequence alignment is evaluated from alignment of the secondary structures in a family of proteins. For the globins, the multiple alignment was on average 99% accurate compared to 90% for pairwise comparison of sequences. For the alignment of immunoglobulin constant and variable domains, the use of many sequences yielded an alignment of 63% average accuracy compared to 41% average for individual variable/constant alignments. The multiple alignment algorithm yields an assignment of disulphide connectivity in mammalian serotransferrin that is consistent with crystallographic data, whereas pairwise alignments give an alternative assignment.

Neural membrane glycoproteins associated with chicken Thy-1: an anti-idiotypic antibody study

In order to investigate the possible binding of Thy-1 to other neuronal cell surface proteins, anti-idiotypic antibodies were raised using a panel of anti-Thy-1 monoclonal antibodies. Anti-idiotypic antibodies were selected for their ability to bind to day-old chick brain membrane components in enzyme-linked immunosorbent assays (ELISA), and to bind to membrane glycoproteins as determined by Western transfer immunoblotting assays. The 5 monoclonal anti-idiotypic antibodies bind to a membrane glycoprotein component of 70 kDa, and one of the antibodies also binds to 3 higher molecular weight components of 160 kDa, 120 kDa and 90 kDa. These antibodies bind to areas of the chicken cerebellum known to be rich in Thy-1. It is postulated that these molecules are associated with Thy-1, and that the role of Thy-1 on the neuronal cell surface, may be to form complexes with, and/or to stabilise these higher molecular weight glycoproteins during synaptic development.

Fibroblasts modulate expression of Thy-1 on the surface of skeletal myoblasts

Thy-1 antigen is a well-characterized cell-surface glycoprotein known to be variably expressed in many different tissues, including lymphocytes, brain, and muscle. Its function remains unknown. In skeletal muscle, both in vivo and in vitro, the antigen has been reported on immature but not on adult tissue, and its disappearance corresponds roughly to the time of myoblast fusion. Using monoclonal H36 antibody to identify myoblasts unambiguously, we demonstrate here that Thy-1 is expressed only on a small (less than 1%) fraction of rat skeletal muscle myoblasts in heterogeneous primary cultures, but the number of myoblasts that express Thy-1 rises to a steady level of about 70% when fibroblasts are removed from secondary cultures. Restitution of fibroblasts or growth of purified myoblasts in medium conditioned by fibroblasts greatly suppresses this increase in myoblast Thy-1 expression. Thus an interaction between fibroblasts and myoblasts, mediated by a soluble nondialyzable molecule, modulates expression of Thy-1 on the myoblast outer membrane.

Cell surface molecules and early events involved in human T lymphocyte activation

The physiologic activation of human T cells by antigen involves events that occur between ligands and receptors at the interface of the T cell and antigen-presenting cell (or target cell). These events have been examined by identifying the cell surface receptors involved in such interactions using mAb. Whereas the T3/T cell antigen receptor plays a central role in such interactions, other T cell receptors have been identified which may also contribute to T cell activation in providing primary activation signals or by functioning as accessory molecules. Although the ligands of these other receptors are currently unknown or ill defined, it is likely that this will provide a fruitful area of investigation. The use of mAb as probes to mimic these putative ligands has facilitated the study of the requirements for activation and the biochemical events initiated by the receptors involved. The T cell receptor, a multisubunit complex, has been most intensively studied. Ligands that bind to T3/Ti cannot initiate activation by themselves and require the participation of accessory molecules. Stimulation of T3/Ti results in the formation of at least two potent intracellular second messengers, IP3 and DG, through the hydrolysis of PIP2. These second messengers, in turn, induce an increase in [Ca2+]i and the activation of pkC. These two events appear to be essential in the transcriptional activation of certain targeted genes through ill-defined pathways leading to the manifestations of T cell activation.

Lymphoma Thy-1 glycoprotein is linked to the cytoskeleton via a 4.1-like protein

In this study we have found that the phosphoprotein doublet of 68,000 and 65,000 daltons (68/65 kD) in mouse T-lymphoma cells shares several structural and functional similarities with erythrocyte band 4.1. Our evidence for identifying the 68/65-kD doublet as a lymphoma 4.1-like protein is as follows: it displays an immunological cross-reactivity with anti-erythrocyte band 4.1 antibody; it exhibits a Svedberg unit of sedimentation coefficient of 4 S; it is phosphorylated in the presence of phorbol ester (phorbol-12-O-tetradecanoylphorbol-13-acetate) and its phosphorylation requires Ca2+; it is phosphorylated primarily at serine residues; and it can bind directly to fodrin (a spectrin-like actin-binding protein). In addition, this lymphoma 4.1-like protein can be both colocalized and coisolated with the major T-lymphocyte-specific glycoprotein, Thy-1 (gp 25). Therefore, all of these results strongly suggest that the lymphoma 4.1-like protein (68/65-kD doublet) may play a pivotal role in linking the Thy-1 (gp 25) glycoprotein to fodrin which, in turn, binds to the actin filaments that are responsible for recruiting Thy-1 antigens into cap structures.

An unexpected sequence homology between link proteins of the proteoglycan complex and immunoglobulin-like proteins

The N-terminal sequence (residues 1-101) of trypsin-link protein from cartilage proteoglycan complex is reported: it presents structural homologies with the poly-Ig receptor and immunoglobulin domains.

Identification of protein sequence homology by consensus template alignment

A pattern-matching procedure is described, based on fitting templates to the sequence, which allows general structural constraints to be imposed on the patterns identified. The templates correspond to structurally conserved regions of the sequence and were initially derived from a small number of related sequences whose tertiary structures are known. The templates were then made more representative by aligning other sequences of unknown structure. Two alignments were built up containing 100 immunoglobulin variable domain sequences and 85 constant domain sequences, respectively. From each of these extended alignments, templates were generated to represent features conserved in all the sequences. These consisted mainly of patterns of hydrophobicity associated with beta-structure. For structurally conserved beta-strands with no conserved features, templates based on general secondary structure prediction principles were used to identify their possible locations. The specificity of the templates was demonstrated by their ability to identify the conserved features in known immunoglobulin and immunoglobulin-related sequences but not in other non-immunoglobulin sequences.

Domain association in immunoglobulin molecules. The packing of variable domains

We have analyzed the structure of the interface between VL and VH domains in three immunoglobulin fragments: Fab KOL, Fab NEW and Fab MCPC 603. About 1800 A2 of protein surface is buried between the domains. Approximately three quarters of this interface is formed by the packing of the VL and VH beta-sheets in the conserved "framework" and one quarter from contacts between the hypervariable regions. The beta-sheets that form the interface have edge strands that are strongly twisted (coiled) by beta-bulges. As a result, the edge strands fold back over their own beta-sheet at two diagonally opposite corners. When the VL and VH domains pack together, residues from these edge strands form the central part of the interface and give what we call a three-layer packing; i.e. there is a third layer composed of side-chains inserted between the two backbone side-chain layers that are usually in contact. This three-layer packing is different from previously described beta-sheet packings. The 12 residues that form the central part of the three observed VL-VH packings are absolutely or very strongly conserved in all immunoglobulin sequences. This strongly suggests that the structure described here is a general model for the association of VL and VH domains and that the three-layer packing plays a central role in forming the antibody combining site.

A glycophospholipid tail at the carboxyl terminus of the Thy-1 glycoprotein of neurons and thymocytes

Cell surface molecules of eukaryotic cells have been considered to be integrated into the membrane bilayer by a transmembrane protein sequence. The Thy-1 antigen of rodent thymocytes and brain was the first eukaryotic membrane molecule for which biochemical data clearly suggested membrane integration via a nonprotein tail. Direct evidence is now presented showing that a glycophospholipid structure is attached to the carboxyl-terminal cysteine residue and that 31 carboxyl-terminal amino acids predicted from the Thy-1 complementary DNA sequence are not present in the mature glycoprotein. These experimental results raise questions concerning signaling across a cell membrane since antibodies to Thy-1 can stimulate T lymphocytes to release lymphokines and undergo cell division.

Anti-Thy-1 antibody responses evoked by Thy-1 antigen expressed in transfected mouse mastocytoma cells and rat fibroblast

The mouse genomic Thy-1.1 gene was isolated from a phage library constructed from AKR/J (Thy-1.1) mouse DNA. Partial nucleotide sequence analysis of the coding region showed that it has only a single nucleotide difference from the Thy-1.2 gene, namely that amino acid 89 reads CGA (Arg) in Thy-1.1 and CAA (Glu) in Thy-1.2, corresponding to the amino acid substitutions previously identified. It was subcloned into an SV-40 derived vector for transfection. Transient transfection into HeLa cells gave 2% positive staining by immunofluorescence. The gene in this vector was also co-transfected into L cells and mastocytoma cells (both of Thy-1.2 strain origin) together with the Agpt gene. L-cell clones selected for transformation proved almost negative for Thy-1.1 expression, and any positive clones gradually lost Thy-1.1 antigen expression in culture. On the contrary, all clones of mastocytoma transformants gave a high level of expression after more than 3 months in culture. The mastocytoma transformants were used to study the immunogenicity of Thy-1.1 molecules expressed on transfected cells. They evoked clear anti-Thy-1.1 plaque-forming cell (PFC) responses both in vivo and in vitro. The mastocytoma transformants also proved able to induce a T-dependent anti-Thy-1.1 antibody response in a cell transfer experiment. The immunogenicity of Thy-1.2 molecules on rat fibroblasts was also studied after transfection with a Thy-1.2 gene cosmid. Although Thy-1.2 expression was very low, these transfectants elicited a clear anti-Thy-1.2 PFC response from AKR spleen cells hyperimmunized against CBA thymocytes.

Chromosomal localization of the human Thy-1 gene

We have isolated the gene coding for human Thy-1. Introduction of this gene into HeLa cells by DNA-mediated transfer results in the expression of Thy-1 antigen on the cell surface. Chromosomal mapping of the Thy-1 gene by hybridization to metaphase chromosomes and Southern blots of DNA from hybrid cells indicate that the Thy-1 gene is located on the long arm of chromosome 11.

Structure of the murine Thy-1 gene

We have cloned the murine Thy-1.1 (AKR) and Thy-1.2 (Balb/c) genes. The complete exon/intron structure and the nucleotide sequence of the Thy-1.2 gene was determined. The gene contains four exons and three intervening sequences. The complete transcriptional unit gives rise to a tissue and developmental stage-specific mRNA of 1850 bp. The 5' end of the gene has multiple initiation sites and a non-TATA box promoter. The 3' end shows a single polyadenylation site after a very long untranslated region.

MRC OX-2 antigen: a lymphoid/neuronal membrane glycoprotein with a structure like a single immunoglobulin light chain

The MRC OX-2 antigen is a rat cell surface glycoprotein of mol. wt. 41 000-47 000 found on neurones, thymocytes, B cells, follicular dendritic cells and endothelium. We now report the amino sequence for this antigen as deduced from the nucleotide sequence of cDNA clones detected by use of an oligonucleotide probe. The sequence contains 248 amino acid residues of which 202 residues are likely to be outside the cell with two domains that show homology with immunoglobulins. The N-terminal domain fits best with Ig V domains and Thy-1 antigen while the C-terminal part is like an Ig C domain. Thus the structure overall is similar to an Ig light chain or the T cell receptor beta chain. Three glycosylation sites are identified on each of the MRC OX-2 antigen domains.