Functional modifications of cytotoxic T-lymphocyte T200 glycoprotein recognized by monoclonal antibodies

B4GALNT2 Controls Sda and SLex Antigen Biosynthesis in Healthy and Cancer Human Colon

The Sd^a carbohydrate antigen and the corresponding biosynthetic enzyme B4GALNT2 are primarily expressed in human normal colonic mucosa and are down‐regulated to variable degrees in colon cancer. On the other hand, the tumor associated antigen SLe^x is not detected in the healthy colon and is upregulated in colon cancer. High level of B4GALNT2 gene expression appears to be a good marker of prognosis in colon cancer; however, the molecular mechanisms regulating these carbohydrate antigens’ expression are still poorly understood. We review here the most recent progress made towards understanding this balanced expression of blood group carbohydrate epitopes Sd^a and SLe^x. In particular in recent years, we have attained a better understanding of genetic and epigenetic regulation of the B4GALNT2 gene and of the subcellular fate of B4GALNT2 isoforms.

Analysis of N- and O-Linked Glycosylation: Differential Glycosylation after Rat Spinal Cord Injury

Glycosylation is a fundamental cellular process that has a dramatic impact on the functionality of glycoconjugates such as proteins or lipids and mediates many different biological interactions including cell migration, cellular signaling, and synaptic interactions in the nervous system. In spinal cord injury (SCI), all of these cellular processes are altered, but the potential contributions of glycosylation changes to these alterations has not been thoroughly investigated. We studied the glycosylation of injured spinal cord tissue from rats that received a contusion SCI. The N- and O-linked glycosylation was assessed at 3 and 14 days post-injury (DPI), and compared with uninjured control and time-matched sham spinal tissue. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and tandem MS (MS/MS) were performed to analyze carbohydrate structures. Results revealed diverse and abundant glycosylation in all groups, with some carbohydrate structures differentially produced in SCI animals compared with uninjured controls and shams. One such change occurred in the abundance of the Sda structure, Neu5Ac-α-(2,3)-[GalNAc-β-(1,4)-]Gal-β-(1,4)-GlcNAc, which was increased in SCI samples compared with shams and non-injured controls. Immunohistochemistry (IHC) and western blot were performed on SCI and sham samples using the CT1 antibody, which recognizes the terminal trisaccharide of Sda with high specificity. Both of these metrics confirmed elevated Sda structure in SCI tissue, where IHC further showed that Sda is expressed mainly by microglia. The results of these studies suggest that SCI causes a significant alteration in N- and O-linked glycosylation.

B4GALNT2 (GALGT2) Gene Therapy Reduces Skeletal Muscle Pathology in the FKRP P448L Mouse Model of Limb Girdle Muscular Dystrophy 2I

Overexpression of B4GALNT2 (previously GALGT2) inhibits the development of muscle pathology in mouse models of Duchenne muscular dystrophy, congenital muscular dystrophy 1A, and limb girdle muscular dystrophy 2D. In these models, muscle GALGT2 overexpression induces the glycosylation of α dystroglycan with the cytotoxic T cell glycan and increases the overexpression of dystrophin and laminin α2 surrogates known to inhibit disease. Here, we show that GALGT2 gene therapy significantly reduces muscle pathology in FKRP P448Lneo(-) mice, a model for limb girdle muscular dystrophy 2I. rAAVrh74.MCK.GALGT2-treated FKRP P448Lneo(-) muscles showed reduced levels of centrally nucleated myofibers, reduced variance, increased size of myofiber diameters, reduced myofiber immunoglobulin G uptake, and reduced muscle wasting at 3 and 6 months after treatment. GALGT2 overexpression in FKRP P448Lneo(-) muscles did not cause substantial glycosylation of α dystroglycan with the cytotoxic T cell glycan or increased expression of dystrophin and laminin α2 surrogates in mature skeletal myofibers, but it increased the number of embryonic myosin-positive regenerating myofibers. These data demonstrate that GALGT2 overexpression can reduce the extent of muscle pathology in FKRP mutant muscles, but that it may do so via a mechanism that differs from its ability to induce surrogate gene expression.

A comparative study of N-glycolylneuraminic acid (Neu5Gc) and cytotoxic T cell (CT) carbohydrate expression in normal and dystrophin-deficient dog and human skeletal muscle

The expression of N-glycolylneuraminic acid (Neu5Gc) and the cytotoxic T cell (CT) carbohydrate can impact the severity of muscular dystrophy arising from the loss of dystrophin in mdx mice. Here, we describe the expression of these two glycans in skeletal muscles of dogs and humans with or without dystrophin-deficiency. Neu5Gc expression was highly reduced (>95%) in muscle from normal golden retriever crosses (GR, n = 3) and from golden retriever with muscular dystrophy (GRMD, n = 5) dogs at multiple ages (3, 6 and 13 months) when compared to mouse muscle, however, overall sialic acid expression in GR and GRMD muscles remained high at all ages. Neu5Gc was expressed on only a minority of GRMD satellite cells, CD8⁺ T lymphocytes and macrophages. Human muscle from normal (no evident disease, n = 3), Becker (BMD, n = 3) and Duchenne (DMD, n = 3) muscular dystrophy individuals had absent to very low Neu5Gc staining, but some punctate intracellular muscle staining was present in BMD and DMD muscles. The CT carbohydrate was localized to the neuromuscular junction in GR muscle, while GRMD muscles had increased expression on a subset of myofibers and macrophages. In humans, the CT carbohydrate was ectopically expressed on the sarcolemmal membrane of some BMD muscles, but not normal human or DMD muscles. These data are consistent with the notion that altered Neu5Gc and CT carbohydrate expression may modify disease severity resulting from dystrophin deficiency in dogs and humans.

The expanding roles of the Sd(a)/Cad carbohydrate antigen and its cognate glycosyltransferase B4GALNT2

BACKGROUND

The histo-blood group antigens are carbohydrate structures present in tissues and body fluids, which contribute to the definition of the individual immunophenotype. One of these, the Sd(a) antigen, is expressed on the surface of erythrocytes and in secretions of the vast majority of the Caucasians and other ethnic groups.

SCOPE OF REVIEW

We describe the multiple and unsuspected aspects of the biology of the Sd(a) antigen and its biosynthetic enzyme β1,4-N-acetylgalactosaminyltransferase 2 (B4GALNT2) in various physiological and pathological settings.

MAJOR CONCLUSIONS

The immunodominant sugar of the Sd(a) antigen is a β1,4-linked N-acetylgalactosamine (GalNAc). Its cognate glycosyltransferase B4GALNT2 displays a restricted pattern of tissue expression, is regulated by unknown mechanisms - including promoter methylation, and encodes at least two different proteins, one of which with an unconventionally long cytoplasmic portion. In different settings, the Sd(a) antigen plays multiple and unsuspected roles. 1) In colon cancer, its dramatic down-regulation plays a potential role in the overexpression of sialyl Lewis antigens, increasing metastasis formation. 2) It is involved in the lytic function of murine cytotoxic T lymphocytes. 3) It prevents the development of muscular dystrophy in various dystrophic murine models, when overexpressed in muscular fibers. 4) It regulates the circulating half-life of the von Willebrand factor (vWf), determining the onset of a bleeding disorder in a murine model.

GENERAL SIGNIFICANCE

The expression of the Sd(a) antigen has a wide impact on the physiology and the pathology of different biological systems.

Distinct contributions of Galgt1 and Galgt2 to carbohydrate expression and function at the mouse neuromuscular junction

At the mammalian neuromuscular junction (NMJ), the CT (cytotoxic T cell) carbohydrate antigen [GalNAcβ1,4[Neu5Ac/Gcα2,3]Galβ1,4GlcNAc-] is a unique synaptic cell surface carbohydrate present in both the presynaptic and postsynaptic membranes. Here we show that Galgt1, which synthesizes the β1,4GalNAc linkage of the CT carbohydrate on gangliosides, is required for presynaptic expression of the CT carbohydrate at the NMJ, while Galgt2, which can synthesize the β1,4GalNAc of the CT carbohydrate on glycoproteins, is required for postsynaptic expression. Proper postsynaptic localization of the CT carbohydrate also required muscle expression of dystroglycan, a known muscle substrate for Galgt2. Transgenic overexpression of Galgt2 in skeletal myofibers altered the expression of synaptic muscle proteins and altered neuromuscular topography, which was partially NCAM-dependent, while an increase in postsynaptic AChR-rich domains was observed in both neuron- and skeletal muscle-specific Galgt2 transgenic mice. By contrast, overexpression of Galgt1 in muscle did not allow for increased expression of CT carbohydrate on the sarcolemmal membrane and instead caused muscle pathology. Loss of Galgt2 increased intracellular accumulation of acetylcholine receptors and acetylcholinesterase within skeletal myofibers, suggesting an additional role for Galgt2 in neuromuscular stability. These experiments demonstrate that Galgt1 and Galgt2 contribute in distinct ways to the expression and function of synaptic βGalNAc-containing carbohydrates at the NMJ.

Glycosylated synaptomatrix regulation of trans-synaptic signaling

Synapse formation is driven by precisely orchestrated intercellular communication between the presynaptic and the postsynaptic cell, involving a cascade of anterograde and retrograde signals. At the neuromuscular junction (NMJ), both neuron and muscle secrete signals into the heavily glycosylated synaptic cleft matrix sandwiched between the two synapsing cells. These signals must necessarily traverse and interact with the extracellular environment, for the ligand-receptor interactions mediating communication to occur. This complex synaptomatrix, rich in glycoproteins and proteoglycans, comprises heterogeneous, compartmentalized domains where specialized glycans modulate trans-synaptic signaling during synaptogenesis and subsequent synapse modulation. The general importance of glycans during development, homeostasis and disease is well established, but this important molecular class has received less study in the nervous system. Glycan modifications are now understood to play functional and modulatory roles as ligands and co-receptors in numerous tissues; however, roles at the synapse are relatively unexplored. We highlight here properties of synaptomatrix glycans and glycan-interacting proteins with key roles in synaptogenesis, with a particular focus on recent advances made in the Drosophila NMJ genetic system. We discuss open questions and interesting new findings driving this investigation of complex, diverse, and largely understudied glycan mechanisms at the synapse.

The Sda/GM2-glycan is a carbohydrate marker of porcine primordial germ cells and of a subpopulation of spermatogonia in cattle, pigs, horses and llama

Spermatogonia are a potential source of adult pluripotent stem cells and can be used for testis germ cell transplantation. Markers for the isolation of these cells are of great importance for biomedical applications. Primordial germ cells and prepubertal spermatogonia in many species can be identified by their binding of Dolichos biflorus agglutinin (DBA). This lectin binds to two different types of glycans, which are α-linked N-acetylgalactosamine (GalNac) and β-linked GalNac, if this is part of the Sda or GM2 glycotopes. We used the MAB CT1, which is specific for the trisaccharides motif NeuAcα2-3(GalNAcβ1-4)Galβ1-, which is common to both Sda and GM2 glycotopes, to further define the glycosylation of DBA binding germ cells. In porcine embryos, CT1 bound to migratory germ cells and gonocytes. CT1/DBA double staining showed that the mesonephros was CT1 negative but contained DBA-positive cells. Gonocytes in the female gonad became CT1 negative, while male gonocytes remained CT1 positive. In immunohistological double staining of cattle, pig, horse and llama testis, DBA and CT1 staining was generally colocalised in a subpopulation of spermatogonia. These spermatogonia were mainly single, sometimes paired or formed chains of up to four cells. Our data show that the Sda/GM2 glycotope is present in developing germ cells and spermatogonia in several species. Owing to the narrower specificity of the CT1 antibody, compared with DBA, the former is likely to be a useful tool for labelling and isolation of these cells.

Overexpression of Galgt2 reduces dystrophic pathology in the skeletal muscles of alpha sarcoglycan-deficient mice

Recent studies have shown that a number of genes that are not mutated in various forms of muscular dystrophy may serve as surrogates to protect skeletal myofibers from injury. One such gene is Galgt2, which is also called cytotoxic T cell GalNAc transferase in mice. In this study, we show that Galgt2 overexpression reduces the development of dystrophic pathology in the skeletal muscles of mice lacking alpha sarcoglycan (Sgca), a mouse model for limb girdle muscular dystrophy 2D. Galgt2 transgenic Sgca(-/-) mice showed reduced levels of myofiber damage, as evidenced by i) normal levels of serum creatine kinase activity, ii) a lack of Evans blue dye uptake into myofibers, iii) normal levels of mouse locomotor activity, and iv) near normal percentages of myofibers with centrally located nuclei. In addition, the overexpression of Galgt2 in the early postnatal period using an adeno-associated virus gene therapy vector protected Sgca(-/-) myofibers from damage, as observed using histopathology measurements. Galgt2 transgenic Sgca(-/-) mice also had increased levels of glycosylation of alpha dystroglycan with the CT carbohydrate, but showed no up-regulation of beta, gamma, delta, or epsilon sarcoglycan. These data, coupled with results from our previous studies, show that Galgt2 has therapeutic effects in three distinct forms of muscular dystrophy and may, therefore, have a broad spectrum of therapeutic potential for the treatment of various myopathies.

The synaptic CT carbohydrate modulates binding and expression of extracellular matrix proteins in skeletal muscle: Partial dependence on utrophin

The CT carbohydrate, Neu5Ac/Neu5Gcalpha2,3[GalNAcbeta1,4]Galbeta1,4GlcNAcbeta-, is specifically expressed at the neuromuscular junction in skeletal myofibers of adult vertebrates. When Galgt2, the glycosyltransferase that creates the synaptic beta1,4GalNAc portion of this glycan, is overexpressed in extrasynaptic regions of the myofiber membrane, alpha dystroglycan becomes glycosylated with the CT carbohydrate and this coincides with the ectopic expression of synaptic dystroglycan-binding proteins, including laminin alpha4, laminin alpha5, and utrophin. Here we show that both synaptic and extrasynaptic forms of laminin and agrin have increased binding to the CT carbohydrate compared to sialyl-N-acetyllactosamine, its extrasynaptically expressed precursor. Muscle laminins also show increased binding to CT-glycosylated muscle alpha dystroglycan relative to its non-CT-containing glycoforms. Overexpression of Galgt2 in transgenic mouse skeletal muscle increased the mRNA expression of extracellular matrix (ECM) genes, including agrin and laminin alpha5, as well as utrophin, integrin alpha7, and neuregulin. Increased expression of ECM proteins in Galgt2 transgenic skeletal muscles was partially dependent on utrophin, but utrophin was not required for Galgt2-induced changes in muscle growth or neuromuscular development. These experiments demonstrate that overexpression of a synaptic carbohydrate can increase both ECM binding to alpha dystroglycan and ECM expression in skeletal muscle, and they suggest a mechanism by which Galgt2 overexpression may inhibit muscular dystrophy and affect neuromuscular development.

Overexpression of Galgt2 in skeletal muscle prevents injury resulting from eccentric contractions in both mdx and wild-type mice

The cytotoxic T cell (CT) GalNAc transferase, or Galgt2, is a UDP-GalNAc:beta1,4-N-acetylgalactosaminyltransferase that is localized to the neuromuscular synapse in adult skeletal muscle, where it creates the synaptic CT carbohydrate antigen {GalNAcbeta1,4[NeuAc(orGc)alpha2, 3]Galbeta1,4GlcNAcbeta-}. Overexpression of Galgt2 in the skeletal muscles of transgenic mice inhibits the development of muscular dystrophy in mdx mice, a model for Duchenne muscular dystrophy. Here, we provide physiological evidence as to how Galgt2 may inhibit the development of muscle pathology in mdx animals. Both Galgt2 transgenic wild-type and mdx skeletal muscles showed a marked improvement in normalized isometric force during repetitive eccentric contractions relative to nontransgenic littermates, even using a paradigm where nontransgenic muscles had force reductions of 95% or more. Muscles from Galgt2 transgenic mice, however, showed a significant decrement in normalized specific force and in hindlimb and forelimb grip strength at some ages. Overexpression of Galgt2 in muscles of young adult mdx mice, where Galgt2 has no effect on muscle size, also caused a significant decrease in force drop during eccentric contractions and increased normalized specific force. A comparison of Galgt2 and microdystrophin overexpression using a therapeutically relevant intravascular gene delivery protocol showed Galgt2 was as effective as microdystrophin at preventing loss of force during eccentric contractions. These experiments provide a mechanism to explain why Galgt2 overexpression inhibits muscular dystrophy in mdx muscles. That overexpression also prevents loss of force in nondystrophic muscles suggests that Galgt2 is a therapeutic target with broad potential applications.

Overexpression of the cytotoxic T cell (CT) carbohydrate inhibits muscular dystrophy in the dyW mouse model of congenital muscular dystrophy 1A

A number of recent studies have demonstrated therapeutic effects of transgenes on the development of muscle pathology in the mdx mouse model for Duchenne muscular dystrophy, but none have been shown also to be effective in mouse models for laminin alpha2-deficient congenital muscular dystrophy (MDC1A). Here, we show that overexpression of the cytotoxic T cell (CT) GalNAc transferase (Galgt2) is effective in inhibiting the development of muscle pathology in the dy(W) mouse model of MDC1A, much as we had previously shown in mdx animals. Embryonic overexpression of Galgt2 in skeletal muscles using transgenic mice or postnatal overexpression using adeno-associated virus both reduced the extent of muscle pathology in dy(W)/dy(W) skeletal muscle. As with mdx mice, embryonic overexpression of the Galgt2 transgene in dy(W)/dy(W) myofibers inhibited muscle growth, whereas postnatal overexpression did not. Both embryonic and postnatal overexpression of Galgt2 in dy(W)/dy(W) muscle increased the expression of agrin, a protein that, in recombinant form, has been shown to ameliorate disease, whereas laminin alpha1, another disease modifier, was not expressed. Galgt2 over-expression also stimulated the glycosylation of a gly-colipid with the CT carbohydrate, and glycolipids accounted for most of the CT-reactive material in postnatal overexpression experiments. These experiments demonstrate that Galgt2 overexpression is effective in altering disease progression in skeletal muscles of dy(W) mice and should be considered as a therapeutic target in MDC1A.

T-cell activation in the curious world of the intestinal intraepithelial lymphocyte

In conventional terms, when T cells encounter appropriate stimuli, they are induced to undergo molecular and physical changes that confer upon them a state of activation. Once initiated, activation generally results in a state of full T-cell responsiveness in an all-or-none manner. Uniquely, however, the intestinal intraepithelial lymphocytes (IELs) bear features that are decidedly different from those of T cells located throughout other immunological compartments in that they exhibit some but not all properties of activated T cells, yet they can be induced to move further into activation provided appropriate costimulatory signals have been received. IEL costimulatory molecules some of which are constitutively expressed, whereas others are upregulated following T-cell receptor (TCR)/CD3 stimulation appear to hold the key to determining the nature and magnitude of the activational process. A system of activation such as this in the intestine would be expected to have great immunological protective value for the host because it would provide an untrammeled process of T-cell activation at a barrier site where the level of antigen exposure is consistently high. Clearly, however, mechanisms must be in place to insure that the IEL activation process is not inadvertently breached. These and other issues central to the operational workings of the intestinal immune system are elaborated in this article, and a model is presented in which IEL activation can be viewed as a layered, three-stage activational process.

Molecular cloning, gene organization and expression of the human UDP-GalNAc:Neu5Acalpha2-3Galbeta-R beta1,4-N-acetylgalactosaminyltransferase responsible for the biosynthesis of the blood group Sda/Cad antigen: evidence for an unusual extended cytoplasmic domain

The nucleotide sequence of the short and long transcripts of beta1,4- N -acetylgalactosaminyltransferase have been submitted to the DDBJ, EMBL, GenBank(R) and GSDB Nucleotide Sequence Databases under accession nos AJ517770 and AJ517771 respectively. The human Sd(a) antigen is formed through the addition of an N -acetylgalactosamine residue via a beta1,4-linkage to a sub-terminal galactose residue substituted with an alpha2,3-linked sialic acid residue. We have taken advantage of the previously cloned mouse cDNA sequence of the UDP-GalNAc:Neu5Acalpha2-3Galbeta-R beta1,4- N -acetylgalactosaminyltransferase (Sd(a) beta1,4GalNAc transferase) to screen the human EST and genomic databases and to identify the corresponding human gene. The sequence spans over 35 kb of genomic DNA on chromosome 17 and comprises at least 12 exons. As judged by reverse transcription PCR, the human gene is expressed widely since it is detected in various amounts in almost all cell types studied. Northern blot analysis indicated that five Sd(a) beta1,4GalNAc transferase transcripts of 8.8, 6.1, 4.7, 3.8 and 1.65 kb were highly expressed in colon and to a lesser extent in kidney, stomach, ileum and rectum. The complete coding nucleotide sequence was amplified from Caco-2 cells. Interestingly, the alternative use of two first exons, named E1(S) and E1(L), leads to the production of two transcripts. These nucleotide sequences give rise potentially to two proteins of 506 and 566 amino acid residues, identical in their sequence with the exception of their cytoplasmic tail. The short form is highly similar (74% identity) to the mouse enzyme whereas the long form shows an unusual long cytoplasmic tail of 66 amino acid residues that is as yet not described for any other mammalian glycosyltransferase. Upon transient transfection in Cos-7 cells of the common catalytic domain, a soluble form of the protein was obtained, which catalysed the transfer of GalNAc residues to alpha2,3-sialylated acceptor substrates, to form the GalNAcbeta1-4[Neu5Acalpha2-3]Galbeta1-R trisaccharide common to both Sd(a) and Cad antigens.

Inhibition of tumor rejection by gammadelta T cells and IL-10

Although many tumors express tumor-specific antigens, most fail to stimulate effective immune responses. Tumors generally lack co-stimulatory molecules, which can lead to tolerance of tumor-specific T cells and progressive tumor growth. Here, we demonstrate that the ovalbumin (OVA) transfected EL4 tumor, E.G7-OVA, grows progressively in syngeneic mice even though the tumor can be rejected if the mice are immunized with OVA in adjuvant. E.G7-OVA grew more rapidly in RAG-1 deficient than sufficient mice suggesting that normal mice make an abortive immune response to this tumor. Depletion of gammadelta T cells or IL-10 augmented the ability of B6 mice to reject E.G7-OVA. Spleen cells from normal, but not IL-10 knockout, mice reconstituted rapid tumor growth in gammadelta T cell-deficient mice. Thus, gammadelta T cells play an important role in preventing immune elimination of this tumor by a mechanism that directly or indirectly involves IL-10.

Definition of pre- and postsynaptic forms of the CT carbohydrate antigen at the neuromuscular junction: ubiquitous expression of the CT antigens and the CT GalNAc transferase in mouse tissues

At the rodent neuromuscular junction, the synaptic expression of the CT carbohydrate antigens is defined by the binding of two monoclonal antibodies, CT1 and CT2. CT1 preferentially stains the presynaptic membrane, while CT2 preferentially stains the postsynaptic apparatus. Here we show that the differential subsynaptic distribution of these antigens is due to a preference of CT1 for structures containing N-acetyl neuraminic acid (NeuAc) and a preference of CT2 for structures containing N-glycolyl neuraminic acid (NeuGc). This was found to be the case both in binding to cultured myotubes, where NeuAc/NeuGc levels were manipulated by feeding acetylated N-acetyl mannosamine precursors, and in binding to purified GM2 ganglioside containing either NeuAc or NeuGc. At human neuromuscular junctions, where the enzymatic machinery to make NeuGc is absent [Proc. Natl. Acac. Sci. USA 95 (1998) 11751], CT1 and GM2(NeuAc) antibodies stained, while CT2 did not. Thus, the N-glycolyl modification of sialic acid helps to define the differential distribution of the CT antigens at the rodent neuromuscular junction, and this difference is lost in humans. In addition, sulfatase and 9-O-acetylesterase treatment of cells or tissues increased the amount of CT1 and CT2 antibody binding, with sulfatase differentially unmasking CT antigen expression on particular glycoproteins. Despite its uniquely synaptic localization in skeletal muscle, the CT antigens and the CT GalNAc transferase are ubiquitously expressed in other mouse tissues, including brain, spinal cord, and peripheral nerve. One of the proteins that can be co-purified with a CT-reactive glycoprotein is alpha dystroglycan. These data better define the sub-synaptic structures of the CT carbohydrate antigens at the neuromuscular junction and demonstrate their ubiquitous presence in mouse tissues, including the brain.

Overexpression of the CT GalNAc transferase in skeletal muscle alters myofiber growth, neuromuscular structure, and laminin expression

Carbohydrates have been shown to mediate or modulate a number of important events in the development of the nervous system; however, there is little evidence that they participate directly in the development of synapses. One carbohydrate structure that is likely to be important in synaptic development of the neuromuscular junction is the CT carbohydrate antigen [GalNAcbeta1,4[NeuAcalpha2,3]Galbeta1(-3GalNAc or -4GlcNAc)]. The synaptic localization of the CT antigen is due to the presence of the terminal beta1,4 GalNAc linkage, and such linkages are localized to the neuromuscular junction in many species. Here we show that an enzyme that can create the synaptic CT structure, the CT GalNAc transferase, is also confined to the neuromuscular junction in mice. Using transgenic mice, we show that overexpression of the CT GalNAc transferase in extrasynaptic regions in skeletal myofibers caused as much as a 60% reduction in the diameter of adult myofibers and an order of magnitude increase in satellite cells. Neuromuscular junctions of transgenic mice had severely reduced numbers of secondary folds, Schwann cell processes were present in the synaptic cleft, and secondary folds were often misaligned with active zones. In addition, multiple presynaptic specializations occurred on individual myofibers. In addition, some normally synaptic proteins, including laminin alpha4, laminin alpha5, utrophin, and NCAM, were expressed along extrasynaptic regions of myofibers. One of the muscle proteins that displayed increased glycosylation with the CT antigen in the transgenic mice was alpha-dystroglycan. These experiments provide the first in vivo evidence that a synaptic carbohydrate antigen has important roles in the development of the neuromuscular synapse and suggest that the CT antigen is involved in controlling the expression of synaptic molecules.

Antigenic epitopes regulate the phenotype of CD8+ CTL primed by exogenous antigens

We previously reported that insulin-specific, MHC class I-restricted CTL precursors can be primed by injecting C57BL/6 mice with bovine insulin in CFA. These bovine insulin-primed CTL displayed a type 0 CTL phenotype, producing IL-4, IL-5, IL-10, low levels of IFN-gamma, but no TNF-alpha. By contrast, CTL generated from C57BL/6 mice primed with OVA in CFA produced IFN-gamma and TNF-alpha but no IL-4, IL-5, or IL-10 and therefore were classified as type 1 CTL. Although CD4+ T cell subsets have been compared extensively in the literature, CTL subsets are less well characterized. Here, the phenotype, function, and requirements for the in vivo activation of type 1 and type 0 CTL cells were studied. Although both types of CTL express many of the same cell-surface Ags, OVA-specific CTL but not bovine insulin-primed CTL expressed CT-1, a carbohydrate epitope of CD45, and bovine insulin-primed CTL but not OVA-specific CTL expressed Fas constitutively. Priming of CTL was abrogated by depletion of phagocytic cells but not CD4+ T cells, whereas depletion of CD4+ T cells but not phagocytic cells inhibited Ab responses in the same mice. Neither endogenous IL-4 nor the dose of priming Ag altered the CTL phenotypes, but the antigenic peptides of OVA and bovine insulin were key to determining the differentiation of either type 1 or type 0 CTL. To our knowledge, this is the first time that antigenic epitopes have been demonstrated to influence the phenotype of Ag-specific CTL responses. These results may be relevant to the development of peptide vaccines in which a particular type of CTL response is desired.

N-acetyllactosamine and the CT carbohydrate antigen mediate agrin-dependent activation of MuSK and acetylcholine receptor clustering in skeletal muscle

Galbeta1,3GalNAc and Galbeta1,4GIcNAc are the subterminal saccharide structures present on the CT carbohydrate antigen GalNAcbeta1,4[NeuAcalpha2,3]-Galbeta1-(3GalNAc or 4GIcNAc)-R, which is localized at the mammalian neuromuscular junction. Here we show that Galbeta1,3GalNAc, Galbeta1,4GIcNAc, and the CT carbohydrate antigen affect postsynaptic assembly in cultured muscle cells. Treatment of C2C12 myotubes with benzyl-O-alpha-GalNAc or neuraminidase increased peanut agglutinin (PNA) expression and AChR clustering. Induction of AChR clustering was blocked by PNA and by muscle agrin. Addition of Galbeta1,4GIcNAc or Galbeta1,3GalNAc increased AChR clustering in myotubes and muscle-specific kinase (MUSK) autophosphorylation in vitro, while NeuAcalpha2,3Galbeta1,4GIcNAc and Galbeta1,4GIc did not. Neural agrin activated MuSK in vitro if the lactosamine-containing mucin domain was present, and this activation was blocked in large part by Galbeta1,3GalNAc and Galbeta1,4GIcNAc. Agrin fragments and MuSK bound to these disaccharides with differing specificities. Overexpression of the CT carbohydrate antigen also increased AChR clustering and MuSK autophosphorylation in the presence of neural agrin. These data suggest a model in which different portions of the CT carbohydrate structure contribute to agrin-dependent signal transduction.

Structural analysis of murine zona pellucida glycans. Evidence for the expression of core 2-type O-glycans and the Sd(a) antigen

Murine sperm initiate fertilization by binding to specific oligosaccharides linked to the zona pellucida, the specialized matrix coating the egg. Biophysical analyses have revealed the presence of both high mannose and complex-type N-glycans in murine zona pellucida. The predominant high mannose-type glycan had the composition Man(5)GlcNAc(2), but larger oligosaccharides of this type were also detected. Biantennary, triantennary, and tetraantennary complex-type N-glycans were found to be terminated with the following antennae: Galbeta1-4GlcNAc, NeuAcalpha2-3Galbeta1-4GlcNAc, NeuGcalpha2-3Galbeta1-4GlcNAc, the Sd(a) antigen (NeuAcalpha2-3[GalNAcbeta1-4]Galbeta1-4GlcNAc, NeuGcalpha2-3[GalNAcbeta1-4]Galbeta1-4GlcNAc), and terminal GlcNAc. Polylactosamine-type sequence was also detected on a subset of the antennae. Analysis of the O-glycans indicated that the majority were core 2-type (Galbeta1-4GlcNAcbeta1-6[Galbeta1-3]GalNAc). The beta1-6-linked branches attached to these O-glycans were terminated with the same sequences as the N-glycans, except for terminal GlcNAc. Glycans bearing Galbeta1-4GlcNAcbeta1-6 branches have previously been suggested to mediate initial murine gamete binding. Oligosaccharides terminated with GalNAcbeta1-4Gal have been implicated in the secondary binding interaction that occurs following the acrosome reaction. The significant implications of these observations are discussed.

Adoptively transferable tolerance induced by CD45RB monoclonal antibody

The phenomenon of rejection remains the most serious problem in transplantation. The ultimate goal in transplant immunology is to develop therapeutic strategies that lead to tolerance. It has been shown that two injections of a monoclonal antibody to CD45RB leads to indefinite acceptance of renal allografts in mice. Moreover, the CD45RB monoclonal antibody reverses acute rejection and still induces tolerance. The purpose of this study was to assess mechanisms that could underlie this therapeutic benefit. It was shown that splenic lymphocytes from tolerant animals augmented proliferation in allogeneic mixed lymphocyte reactions against donor alloantigens, and the serum of tolerant mice contained donor-specific antibodies, mainly of the IgG1 isotype, suggesting the presence of TH2 cytokines. Tolerance could not be broken by interleukin-2 infusion, but tolerance could be adoptively transferred by transfusion of tolerant mouse CD4+ splenic lymphocytes into naive allografted animals. These data suggest that an active immunoregulatory mechanism is partly responsible for the therapeutic effect. CD45RB-directed therapy may find clinical application in organ transplantation in human patients.

Distinct structures and functions of related pre- and postsynaptic carbohydrates at the mammalian neuromuscular junction

Carbohydrates that terminate in beta-linked N-acetylgalactosamine (betaGalNAc) residues are concentrated in the postsynaptic apparatus of the skeletal neuromuscular junction and have been implicated in the differentiation of the postsynaptic membrane. We now report that distinct synapse-specific betaGalNAc-containing carbohydrates are associated with motor nerve terminals. Two monoclonal antibodies that recognize distinct betaGalNAc-containing epitopes, CT1 and CT2, both stain synaptic sites on skeletal muscle fibers. However, CT1 selectively stains nerve terminal, whereas CT2 selectively stains the postsynaptic apparatus. Likewise, CT1 and CT2 selectively stain motoneuron-like and muscle cell lines, respectively. Using the cell lines, we identify distinct CT1- and CT2-reactive glycolipids and glycoproteins. Finally, we show that GalNAc modulates the adhesion of motoneuron-like cells to recombinant fragments of a synaptic cleft component, laminin beta2. Together, these results show that pre- as well as postsynaptic membranes bear and are affected by distinct but related synapse-specific carbohydrates.

Cell-type specificity of anti-CD45 autoantibodies in systemic lupus erythematosus

OBJECTIVE

To determine the specificity of anti-CD45 autoantibodies in systemic lupus erythematosus (SLE) for native CD45 and for CD45 expressed by T cells and B cells, and at different stages of cellular activation.

METHODS

CD45 purified from different types of lymphocytes was examined by immunoblotting with sera from patients with SLE. Indirect immunofluorescence experiments were performed with purified anti-CD45 autoantibodies.

RESULTS

IgM anti-CD45 autoantibodies in SLE recognize native CD45 expressed on the surface membrane of viable lymphocytes and CD45 purified from activated peripheral T cells and certain T cell lines, but not CD45 purified from B cells or resting peripheral T cells. The presence or absence of reactivity is independent of the individual isoforms expressed.

CONCLUSION

Recognition of CD45 by IgM antilymphocyte autoantibodies in SLE varies with the lineage and state of activation of the lymphocyte target. This pattern of reactivity is consistent with autoantibody specificities involving CD45 glycoforms, rather than CD45 isoforms.

Molecular interactions in the activation of effector and precursor cytotoxic T lymphocytes

Cell-cell interactions are influenced by parameters that cannot readily be studied using either intact cells or soluble molecules. Replacing one of the pair of interacting cells with an artificial cell surface construct allows novel insights to be gained into some of these parameters. Application of this approach to the study of CTL has helped to clarify the contrasting roles of some of the various receptors that are involved in recognition, adhesion and activation. In addition, it has revealed features of these receptor ligand interactions that help to explain how CTL are able to carry out effective immune surveillance and elimination of virus-infected or tumor cells. Although not discussed in this review, artificial cell surface constructs have also been effectively employed to study the interaction of TH cells with class II bearing surfaces. Class I protein and peptide antigen can be sufficient to mediate adhesion and activate CTL effector function through the TCR and CD8. In addition, interactions of other co-receptors with their ligands can act along with TCR and CD8 in a cascade of activated adhesion and co-stimulatory signal generation to allow adhesion and response when antigen and/or class I surface densities are too low to be sufficient by themselves to initiate response. The relative contributions of the various receptor/ligand interactions to a given CTL/target encounter will depend upon the affinity of the TCR for antigen and on the densities and types of ligands, including antigen, displayed on the target cell surface. It appears that the CTL has the ability to accomplish its task in a variety of ways, providing it with considerable flexibility in recognizing and eliminating antigen-bearing target cells. Thus, downregulation of any one particular ligand on a virus-infected or tumor cell does not allow escape from CTL surveillance provided that at least a low level of class I antigen remains present. The CTL is able to employ several co-receptors specific for ligands common to many cell types without being diverted from effective immune surveillance, since these receptors only become activated to mediate high-avidity adhesion when antigen is detected by the TCR. Cloned effector CTL are most amenable to studies of the kind reviewed here, since large numbers of homogenous cells can be obtained, antigen-specific adhesion can be readily measured and response is rapid and easily quantitated.(ABSTRACT TRUNCATED AT 400 WORDS)

Ovalbumin injected with complete Freund's adjuvant stimulates cytolytic responses

CD8+ cytotoxic T lymphocytes (CTL) recognize antigens (Ag) associated with class I major histocompatibility complex (MHC) molecules. Endogenously synthesized protein Ag are processed into peptides in the cytoplasm and transported to the endoplasmic reticulum where they are bound by class I proteins. Exogenous Ag do not enter the class I processing pathway of most cells and thus do not activate CD8+ CTL. Nevertheless, several investigators have reported that immunization with exogenous Ag can activate CD8+ T cells that have immunoregulatory activity. To determine how exogenous Ag entered the class I pathway in vivo and whether immunosuppressive CD8+ T cells were cytolytic, we have shown in this report that injection with OVA emulsified in the complete Freund's adjuvant (CFA) primed CD8+, class I MHC-restricted, OVA-specific CTL in mice. These CTL recognize the OVA257-264 epitope, produce tumor necrosis factor-alpha and interferon-gamma upon activation. Both oil and mycobacteria components in CFA were required for inducing CTL responses. Priming was not attributed to direct sensitization of class I-bearing cells by contaminating peptides. Rather, phagocytic cells, but not CD4+ helper T cells, were required for priming CD8+ CTL by OVA-CFA. Thus, OVA in CFA is taken up by antigen-presenting cells and processed into the class I pathway by phagocytic cells in vivo. In addition, CTL induced by OVA-CFA suppressed the antibody response to OVA in adoptive recipients. These results suggest that CD8+ CTL specific for exogenous proteins might be routinely stimulated by injecting proteins in conventional adjuvants and that such cells have the potential to regulate immune responses in vivo.

The expression of carbohydrate antigens in activated T cells and in autoimmune diseases

Cell surface carbohydrate antigens have been implicated in cell differentiation and maturation and may play a role in immunoregulation. The expression of carbohydrates in peripheral blood lymphocytes (PBL) was studied by double immunofluorescence flow cytometry, using MoAbs CT1 and CT2 but only a small proportion of cells bound these MoAbs. MoAbs CT1, CT2 and the lectin vicia villosa (VV) which share specificity for Gal NAc were then used to examine lymphocytes from patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), Behcet's disease (BD) and IgA nephropathy. A significant increase in MoAbs CT1 CT2 and VV binding CD4 or CD8 cells was found only with lymphocytes from patients with SLE. However, MoAbs CT or VV binding lymphocytes from healthy subjects were significantly up-regulated by activation with a mitogen (PHA), cross-linked anti-CD3 MoAb or a common antigen (65kDa heat shock protein), suggesting that an increased proportion of T cells expressing these carbohydrates results from any of the three types of lymphocyte activating agents. Inhibition studies were then carried out to determine the relationship between the MoAbs CT1 and CT2, VV and GalNAc. Indeed, VV binding to T cells was significantly inhibited by either MoAbs CT1 or CT2, or GalNAc but not GlucNAc, suggesting that VV shares a common binding site with MoAb CT and that GalNAc may constitute one of the sugar receptors. Investigations of lymphocytes from adult peripheral blood in health and disease suggest that carbohydrate antigens may play a role in activation and immunoregulation.

Carbohydrate specificity of IgM autoantibodies to CD45 in systemic lupus erythematosus

Patients with SLE develop IgM autoantibodies to different isoforms of CD45, the major surface membrane protein tyrosine phosphatase on lymphocytes and other nucleated hemopoietic cells. Because such autoantibodies could have a potential role in the development of immune dysfunction in this disorder, we performed a series of experiments to characterize their antigenic specificity further. Blots of recombinant E. coli fusion proteins encoded by exons 3-7 of the p220 and p180 isoforms were uniformly non-reactive with SLE IgM, suggesting that anti-CD45 autoantibodies in SLE are directed against conformational and/or carbohydrate epitopes, rather than linear polypeptide epitopes. This issue was examined further using chemically and enzymatically modified CD45 purified from T cells by lectin affinity chromatography as substrates. Treatment of CD45 with 25 mM sodium-m-periodate, sufficient to abrogate binding to various lectins, abolished the reactivity with SLE anti-CD45 autoantibodies. On the other hand, digestion of CD45 with neuraminidase enhanced the binding of anti-CD45 autoantibodies from some of the SLE sera. This result probably reflects decreased steric hindrance or charge repulsion because the binding of mouse monoclonal antibodies directed against linear polypeptide epitopes of CD45 was similarly enhanced. Digestion of CD45 with N-glycosidase F had no effect on autoantibody staining. Taken together, these data suggest that IgM anti-CD45 autoantibodies in SLE recognize non-sialylated carbohydrate determinants in the highly O-glycosylated polymorphic domains of CD45.

Activation of T cells through a T cell-specific epitope of CD45

The 180- and 190-kDa isoforms of CD45 are preferentially expressed on the helper inducer (memory) subset of CD4 cells. In order to generate monoclonal antibodies against the extracellular domains of these isoforms and determine whether they could regulate the function and activation of these cells, we developed a mAb, anti-4H2D, by immunizing Balb/c mice with an isogenic mouse pre-B cell line expressing the human 190-kDa CD45 isoform. Anti-4H2D reacts with approximately 60% of T cells, 70% of CD4 cells, and 60% of CD8 cells. The CD4 cell population defined by this mAb corresponds functionally and phenotypically to that defined by the CD45RO+CD29+ subset. Western blotting demonstrated that anti-4H2D reacts primarily with the 190-kDa isoform of CD45 and to a minor extent, the 205- and 180-kDa CD45 isoforms. Interestingly, this mAb reacted with only a subpopulation of mature thymocytes and peripheral T cells, despite the fact that the 190-kDa CD45 isoform, as well as CD45RO and CD29, is more widely distributed on cells of hematopoietic origin. The 4H2D epitope was neuraminidase sensitive, indicating that anti-4H2D reacts with a carbohydrate epitope which is present on only a subset of the T cells containing the 190-kDa CD45 isoform epitopes. Functional studies showed that soluble anti-4H2D augmented T cell proliferation induced by the CD2 and CD3 pathways, and treatment of T cells with this mAb up-regulated [Ca2+]i flux induced by both anti-CD2 and anti-CD3 mAbs. These results suggest that the 190-kDa CD45 isoform on human CD4 cells is heterogeneous and that the 190-kDa isoform recognized by anti-4H2D regulates the function and activation of CD4 helper T cells.

Autoantibodies to CD45 in systemic lupus erythematosus

Autoantibodies to surface antigens on lymphocytes and other cells of the immune system may contribute to the development of immunoregulatory and other cellular immune abnormalities in patients with active systemic lupus erythematosus. Of special interest in this respect are autoantibodies to CD45 (leukocyte-common antigen, T200), a plasma membrane protein tyrosine phosphatase implicated in the regulation of lymphocyte functional activity, including cytotoxicity, proliferation, and differentiation.

A program to facilitate cytotoxicity assay data reduction

A report of a program which performs the initial computational reduction of the raw data from a cytotoxicity assay and outputs the reduced data as an image of the arrangement of the assay(s) upon the microwell plate. The program accepts the raw data either as manual or diskette file input.

Structure-function relationship and immunochemical mapping of external and intracellular antigenic sites on the lymphocyte activation inducer molecule, AIM/CD69

Human activation inducer molecule (AIM/CD69), a dimeric glycoprotein structure of 33 and 27 kDa, is the earliest inducible cell surface antigen expressed during lymphocyte activation and is implicated in the induction of T and B cell proliferative responses. Cross-competition monoclonal antibodies (mAb) binding assays have allowed the definition of four antigenic epitopes. Three of them (antigenic sites E1-3) are extracellular while the fourth (site I) is a sequential epitope localized intracellularly and highly conserved interspecies. Site E1 is shown to be an immunodominant antigenic determinant closely related to a functional domain of AIM important for triggering of T cell proliferation. Studies of peptide fragmentation of the two isolated AIM subunits with different proteases have demonstrated that both AIM chains are differentially glycosylated forms of a single 24-kDa core protein. Moreover, the two denatured and isolated AIM chains share common epitope(s) as demonstrated by their reactivity with an mAb by both Western blot analysis and immunoprecipitation of the separated AIM subunits. Biosynthesis studies revealed the rapid appearance of two intermediate precursor forms of 29 and 26 kDa which arise from the 24-kDa unglycosylated AIM polypeptide. This 24-kDa unglycosylated form could be also precipitated from iodinated cells pretreated with tunicamycin, indicating that glycosylation of the protein was neither required for AIM cell surface expression nor for acquisition of external epitopes E1-E3. Cell treatment with pronase resulted in the loss of the external epitopes E1-3 and the generation of a proteolytic peptide of 16 kDa that could be precipitated by the anti-AIM mAb specific for the internal site I. This proteolytic fragment retained the transmembrane and cytoplasmic regions of the molecule where both epitope I and phosphorylation sites reside. These results demonstrate that AIM is an integral membrane homodimeric glycoprotein with a large cytoplasmic domain probably involved in the activation signals transduced through this molecule to lymphocytes.

Differential effects of CD45 CD45R and CD45R0 monoclonal antibodies in modulating human B cell activation

We have examined the effect of monoclonal antibodies (MoAbs) to different epitopes of the leucocyte common antigen (LCA), CD45, on anti-human immunoglobulin-primed B cell activation. Binding of MoAbs to restricted epitopes present on CD45 glycoproteins of 180 kD and 220 kD (designated CD45R0 and CD45R, respectively) was found to promote B cell proliferation in the presence of T cells. CD45 MoAbs reactive with 'public' determinants on all four constituent members of the LCA family (180, 190, 205, and 220 kD) had either little effect or inhibited the basal B cell response to anti-immunoglobulin priming. Simultaneous immunofluorescent analysis of 5-bromodeoxyuridine incorporation and the expression of CD19 (B cell specific) or CD2 (T cell specific) identified the majority of responder cells as B lymphocytes. CD45R MoAbs significantly enhanced the B cell response to sub-optimal concentrations of interleukin-2. CD45 and CD45R0 MoAbs failed to elicit a similar response. Antibody to the interleukin-2 receptor (anti-Tac) partially blocked the CD45R-driven, T cell-dependent B cell proliferation.

Glycosylation of CD45: carbohydrate composition and its role in acquisition of CD45R0 and CD45RB T cell maturation-related antigen specificities during biosynthesis

The contribution of oligosaccharides to the biochemical composition and antigen heterogeneity of the phosphotyrosine phosphatase CD45 glycoproteins has been studied on the K-562 erythroleukemic cell line. Treatment of immunoprecipitated CD45 glycoproteins with distinct exo- and endoglycosidases revealed the presence of highly sialylated O- and N-linked complex carbohydrates in the composition of mature CD45 glycoproteins. Incubation of K-562 cells with the N-glycosylation inhibitor tunicamycin blocked carbohydrate processing during biosynthesis of CD45 proteins, generating unglycosylated polypeptides similar in size to those resulting from digestion of CD45 proteins with a mixture of both N- and O-glycanases. Epitopes defining the T cell maturation related CD45R0 and CD45RB antigen specificities were present on the mature 180- and 190-kDa K-562 CD45 proteins, respectively. However, the CD45R0 and CD45RB epitopes were not detected on the high mannose biosynthetic CD45 precursors. Furthermore, treatment of CD45 proteins with O-glycanase or neuraminidase resulted in the loss of both CD45R0 and CD45RB epitopes, although reactivity of the anti-CD45R0 and anti-CD45RB mAb was not affected by mAb preincubation with either sialic acids or sialyllactose in solution. From these results we conclude that the blockade of early steps of N-glycosylation during carbohydrate processing resulted in the inhibition of subsequent incorporation of O-linked sugars on CD45 polypeptides, thus preventing the late acquisition of the CD45R0 and CD45RB determinants on the 180- and 190-kDa CD45 polypeptides.

Differential effects of anti-CD45 monoclonal antibody on human B cell proliferation: a monoclonal antibody recognizing a neuraminidase-sensitive epitope of the T200 molecule enhances anti-immunoglobulin-induced proliferation

We have generated seven monoclonal antibodies (mAb) that recognize the T200 molecule. These mAb have been classified by competitive binding assay in flow cytometry into three groups each reacting with a different epitope of the T200 molecule: (a) 136-4B5, that shows a sialic acid nature, (b) 135-4H9, 135-4C5, 144-2, 155-2 and (c) 72-5D3, 124-2H12b. A heterogeneous effect was observed when they were tested on an anti-immunoglobulin-induced B cell proliferation. Whereas 72-5D3 and 135-4H9 mAb inhibited the proliferative response of B cells, 136-4B5 mAb greatly enhanced it, both effects being dose dependent. We can conclude that anti-CD45 mAb have a different and contrary functional behavior on anti-Ig-induced B cell proliferation, depending on the epitope recognized. The basis for such a difference could reside in the glucidic nature of the epitope recognized by the 136-4B5 mAb.

Effect of activation of protein kinase C on CD45 isoform expression and CD45 protein tyrosine phosphatase activity in T cells

The T200/leukocyte common antigen (CD45) is a family of at least five large-molecular weight glycoproteins, which are differentially expressed on T cell subsets. The CD45 antigen consists of a variable heavily glycosylated exterior domain, a single membrane-spanning region, and a large cytoplasmic domain that has protein tyrosine phosphatase (PTPase) activity. In this study, we examined the effects of activation of protein kinase C (PKC) on the phosphorylation and expression of CD45 isoforms and PTPase activity in human T cells. After activation of PKC by phorbol 12-myristate 13-acetate (PMA), CD45RA expression rapidly increased within the first 24 h, whereas CD45R0 expression did not change within this time. However by 48 h, expression of CD45R0 also began to increase. Metabolic labeling showed that the rapid increment in CD45RA expression observed after PMA stimulation is primarily due to increased de novo synthesis of the 205-kDa and not the 220-kDa molecule. PMA treatment resulted in the phosphorylation of each CD45 isoform to a degree corresponding to its relative surface expression. Significantly, we found that the phosphorylation of CD45 by PKC activation down-regulated CD45 PTPase activity.

Involvement of CD45 in MHC class II-allospecific cytotoxicity

Twenty-seven different CD45 monoclonal antibodies (mAb) were assessed for their ability to block cytotoxicity of alloreactive CD4+ MHC class II-specific or CD8+ class I-specific human T cell clones (n = 3 and 5, respectively). Twelve of 27 blocked the former but only 1/27 the latter, although all 27 significantly inhibited MHC-unrestricted lysis of K562 cells by either CD4+ or CD8+ clones. MAb pretreatment of effector cells but not target cells resulted in retention of blocking. Crosslinking the CD45 with goat anti-mouse Ig serum did not result in blockade of lysis by class I-specific clones or reveal blocking of class II-specific clones not inhibited by mAb alone. These results suggest that CD45 molecules may be predominantly involved in MHC class II-specific but not class I-specific allocytotoxicity as well as MHC-unrestricted natural killer-like cytotoxicity.

Further data on the selective expression of Ly-5 isoforms

Ly-5 (CD45) glycoproteins of the mouse, expressed by all or most hematopoietic cell lineages and specified by a single Ly-5 gene, range in size from isoform T200 of T cells (the smallest), in which exons 4, 5, and 6 are not represented, to isoform B220 of B cells (the largest), in which all three of these optional exons are represented. The main purpose of the present study, utilizing the polymerase chain reaction (PCR), was to ascertain whether known isoforms of intermediate size are generated by single or dual usage of optional exons 4, 5, and 6. Transcripts representing all eight isoforms predictable from varied use of three exons were observed among a diverse panel of nine B-cell tumors in culture, but there was no evident concordance with known contrasting differential features that distinguish members of the B-cell tumor panel. No two B tumors exhibited the same variety of transcripts and the relative quantities of transcripts expressed varied greatly from tumor to tumor. Cloning of B-cell tumors did not alter their distinctive transcript patterns. Separation methods (sodium dodecyl sulfate polyacrylamide gel electrophoresis; SDS-PAGE) did not suffice to segregate all corresponding expressed isoforms but did establish that transcripts representing usage of a single optional exon and of two optional exons were actually translated, which supports a provisional inference that all eight isoforms exist. The considerable diversity of B-cell transcript phenotypes was not seen among seven T-cell leukemias, two cytolytic T-cell lines, and three Th 1 helper T-cell lines, all of which displayed a uniform phenotype comprising major expression of the T200 transcript (no optional exon) and minor expression of a transcript employing exon 5. However, a panel of five cloned Th2 T-cell lines, which represent a second and functionally different branch of the helper/inducer T-cell category, exhibited a characteristic transcript pattern which distinguished them from a panel of three Th1 T-cell lines. The major transcript in the Th2 lines was also T200, but the Th2 lines showed higher representation of transcripts containing optional exons. A single Th2 clone expressed an unusual transcript suggesting a potential isoform not compounded simply by varied inclusion of the three identified optional exons. After activation of the helper T-cell lines with concanavalin A (Con A), expression of transcripts containing optional exons appeared to decrease.

Intraepithelial lymphocytes. Anatomical site, not T cell receptor form, dictates phenotype and function

The function and structure of the TCR proteins of intraepithelial lymphocytes (IEL) were examined using a panel of mAbs specific for TCR-gamma/delta. Three subsets of TCR-gamma/delta+ IEL could be detected with five mAbs, termed GL1-GL5. The mAbs were able to trigger lysis via crosslinking of the IEL TCR and all of the subsets were constitutively cytolytic. Immunoprecipitation of IEL TCR proteins revealed that the GL2 mAb reacted only with gamma, delta heterodimers containing high Mr delta chains, while the other mAbs precipitated all of the observed gamma and delta proteins. Two-color fluorescence analysis showed that the GL2+ subset was contained within the larger GL1+ subset. The GL3 and GL4 mAbs appear to be specific for all TCR-gamma/delta while GL2 was V delta 4 specific. Analysis of IEL for TCR-alpha/beta expression demonstrated that approximately 20% of B6 IEL were TCR-alpha/beta+. Interestingly, this population of IEL contained Thy-1- and CT1+ cells, indicating that the unique phenotype of IEL was not restricted to TCR-gamma/delta+ cells. Moreover, the TCR-alpha/beta+ IEL were also constitutively cytolytic, suggesting that the intestinal milieu was controlling the functional programming of IEL regardless of TCR type. The mAbs reported here as well as the ability to exploit the distinct phenotype of IEL should prove useful in determining the function of IEL and the TCR-gamma/delta.

Concanavalin A induces a cytoskeletal association of T200 molecules in T lymphocytes

A recent report indicated that T200 molecules interact with elements of the cytoskeleton in BW5147 T lymphoma cells. We have confirmed the cytoskeletal association of T200 by examining nonionic detergent-soluble and detergent-insoluble fractions of murine T cell tumor cell lines, cloned cytotoxic T lymphocyte lines, and thymocytes. Concanavalin A (Con A)-treated and untreated cells were extracted with 0.5% Triton X-100 and the remaining insoluble material was extracted under conditions allowing actin depolymerization. In the absence of Con A treatment, little T200 could be recovered from the depolymerized insoluble fraction. However, in T cells treated with capping concentrations of Con A, a considerable amount of T200 was rendered insoluble in nonionic detergent, and T200 could be recovered from the insoluble fraction by a buffer which dissociates actin polymers. A lesser, but still significant, amount of T200 associated with the detergent-insoluble fraction of thymocytes treated with concentrations of Con A and succinyl Con A, which are mitogenic for T cells. We also found that in T cells treated with mitogenic concentrations of succinyl Con A, more T200 associated with cytoskeleton than did H-2 or LFA-1 molecules. Because T200 is such a predominant molecule on the surface of T cells, such translocations of the molecule may have a major impact on the physiology of the cell, especially if T200 functions as a protein tyrosine phosphatase as recent evidence by others suggests.

Molecular interactions, T-cell subsets and a role of the CD4/CD8:p56lck complex in human T-cell activation

Several T-cell structures are capable of generating intracellular signals linked to T-cell proliferation. Crosslinking of CD2, CD4 and CD45 with Ti/CD3 to several of these antigens can augment the minimal signal induced by antigen binding to the Ti/CD3 complex. Importantly, some of these regulatory structures (CD4, CD8 and CD45) are also expressed on subsets of T cells with distinct activation requirements and functional programs (helper, suppressor, suppressor-inducer and cytotoxic function). The CD4+ CD45RA+ (2H4+) subset responds well to self-Ia, poorly to soluble antigen and possesses suppressor-inducer function. A reciprocal subset CD4+ CD45RA- (4B4+) is preferentially activated by soluble recall antigens and possesses helper function. Each of these subsets can be distinguished by virtue of the differential expression of CD45 antigens. Importantly, the anti-2H4 antibody which reacts with a specific region near the N-terminus of two CD45 isoforms can effectively block its function. Crosslinking of CD4 with the Ti/CD3 complex preferentially activated the CD4+ CD45+ RA- subset, while soluble antibodies to CD2 preferentially affected the CD45 CD45RA+ subset. Thus, CD3 and CD4 more effectively synergize in the activation process on the CD4+ CD45RA- subset, a result consistent with the ability of this subpopulation to respond to recall antigens. The regulatory role of the CD4, CD8 and CD45 antigens may be mediated by an interactive network of protein-tyrosine phosphorylation and dephosphorylation. We have shown the CD4 and CD8 antigens to be associated with the T cell-specific protein-tyrosine kinase (p56lck). p56lck is a member of a family of protein-tyrosine kinases with an established ability to activate and transform mammalian cells. The CD4/CD8:p56lck complex is catalytically active as shown by its ability to phosphorylate various members of the Ti/CD3 complex. By contrast, the CD45 antigens possess protein-tyrosine phosphatase activity within their intracellular domains and are postulated to function by virtue of a regulatory interaction with CD4/CD8:p56lck and its potential substrates. Thus, the differences in the response of the CD4+ CD45RA+/- subsets to various stimuli and the expansion of T-cell subsets with distinct immunoregulatory programs may be governed by a pathway of tyrosine-mediated events.

Poly[N-acetyl-lactosamine]-type sugar chains in CD45 antigens of abnormal T cells of lpr mice are different from those of normal T cells and B cells

The lymph node (LN) T cells from autoimmune MRL/MpJ-lpr/lpr (lpr) mice and control MRL/MpJ-+/+ (+/+) mice were compared as to their cell surface lectin binding sites and the glycoproteins responsible for the lectin binding. T cells from enlarged lymph nodes of lpr mice were found to express more binding sites for lectins which are reactive to poly[N-acetyl-lactosamine]-type sugar chains than normal +/+ mouse lymph node T cells. Furthermore, we found that high mol. wt (180,000-220,000) glycoproteins on lpr T cells were strongly stained with these poly [N-acetyl-lactosamine]-binding lectins on Western-blotting. These glycoproteins were found to belong to the CD45 family on immunoprecipitation and absorption with monoclonal anti-CD45 antibody. Thus, aberrant expression of high mol. wt CD45 (CD45R) antigens on lpr T cells may contribute greatly to the strong reaction of these cells with poly[N-acetyl-lactosamine]-binding lectins. We also found that poly[N-acetyl-lactosamine]-type sugar chains are more abundant on B cells than on lpr T cells, and that the molecular weights and the carbohydrate moieties of CD45R antigens on lpr T cells are different from those of CD45R antigens on +/+ spleen B cells.

Selective expression of CD45 isoforms and of maturation antigens during human thymocyte differentiation: observations and hypothesis

Selective expression of high and low molecular weight isoforms of CD45 (T200) occurs coincident with activation of mature T lymphocytes. Expression of CD45 p180 and CDw29 defines antigen-experienced memory T cells in the periphery, and expression of CD45R (CD45 p205/220) defines naive T cells. Upon activation, CD45R+ T cells lose CD45R and acquire CD45 p180 and high density CDw29. In this review we discuss the expression of CD45 isoforms, CDw29, pgp-1 and CD1 on human thymocytes and develop the hypothesis that expression of CD45R marks the generative thymic lineage while expression of CD45 p180 marks those cells destined for intrathymic death. This hypothesis is supported by evidence from phenotypic, molecular and functional analysis of thymocyte subsets. We propose that expression of high molecular weight isoforms of CD45 is essential for growth and differentiation of immature T cells and that inappropriate rearrangement or specificity of TCR activates a transition from expression of CD45R to that of CD45 p180 and intrathymic death.

Expression and function of AIM, an activation inducer molecule of human lymphocytes, is dependent on the activation of protein kinase C

AIM is an activation inducer molecule selectively expressed by activated lymphocytes through which agonistic proliferative signals can be triggered. The relationship between the expression of AIM with the activation of protein kinase C (PKC) has been studied. Different activators of PKC such as the active phorbol esters, phorbol myristate acetate and phorbol dibutyrate, or the phorbol-related ester mezerein were able to induce AIM expression on peripheral blood lymphocytes as assessed by immunofluorescence flow cytometry. Moreover, the expression of this activation antigen was also induced by treatment of peripheral blood lymphocytes either with dioctanoyl-rac-glycerol, a synthetic analogue of diacylglycerol, the physiological mediator of PKC activation. Further indirect evidence that AIM expression was dependent on the activation of PKC was obtained by blockade of the induction of its expression in cells treated with H7, an inhibitor of PKC. The AIM expression can be detected as early as 3 h after addition of phorbol esters and it requires active RNA and protein synthesis. The activation of PKC appears to be also required in the proliferative response induced by anti-AIM monoclonal antibody (mAb) in conjunction with phorbol esters. Agents such as phorbol myristate acetate, phorbol dibutyrate or mezerein but not the inactive phorbol ester methyl-phorbol myristate acetate induced a high proliferation of peripheral blood lymphocytes in the presence of anti-AIM mAb. In addition, we have demonstrated that the anti-AIM mAb is not sufficient by itself to induce cellular proliferation once the AIM antigen is expressed at the cell surface, requiring the simultaneous stimulation of the PKC to trigger high proliferative responses. Furthermore, the anti-AIM mAb did not appear to exert its effect on proliferation by rapidly increasing the intracytoplasmic Ca2+ levels. Taken together all these results indicate that the expression and function of AIM antigen is dependent on the activation of PKC.

Functional characterization of the CD45R (2H4) molecule on CD8 (T8) cells in the autologous mixed lymphocyte reaction system

In the present study, we have investigated the molecular basis for the immunoregulatory function of CD8 cells after autologous mixed lymphocyte reaction (AMLR) activation. We demonstrated that the CD8+CD45R+, but not the CD8+CD45R- subset of cells effected suppression following AMLR activation. In contrast, cytotoxic activity against alloantigens resided in both the CD8+CD45R+ and CD8+CD45R- subsets of cells. Biochemical analysis showed that on CD8 cells, the 220-kDa isoform of the LCA/T200 antigen family was better represented than the 200-kDa isoform, when compared to CD4 cells. The density of the CD45R antigen increased on CD8 cells following activation in AMLR and treatment of AMLR-activated CD8 cells with either anti-CD45R antibody or anti-CD3 antibody abolished the suppressor function of these cells. In contrast, treatment of AMLR-activated CD4 cells with anti-CD45R, but not anti-CD3 antibody, abolished the suppressor/inducer function of these cells. The results suggest that the CD45R antigen as well as CD3 T cell receptor complex have an important role in the suppressor function of AMLR-activated CD8 cells.

Organization of the Ly-5 gene

A single Ly-5 gene is known to generate a variety of transmembrane glycoprotein isoforms that distinguish various cell lineages and stages of differentiation within the hematopoietic developmental compartment of the mouse. Systems homologous to Ly-5 are known in rats and in humans. The complete exon-intron organization of the Ly-5 gene is described in this report. The Ly-5 gene occupies about 120 kilobases of chromosome 1 and comprises 34 exons, of which 32 (Ex-3 to Ex-34) are protein coding. Ex-1, Ex-2, and parts of Ex-3 and Ex-34 are untranslated. In all cDNA clones examined, either Ex-1 or Ex-2 was represented, but not both, implying that Ex-1 and Ex-2 in Ly-5 mRNA may be mutually exclusive. Primer extension and S1 nuclease protection mapping were used to identify initiation (cap) sites for transcription. The finding of putative cap sites for Ex-1 and Ex-2, and of corresponding TATA-like sequences, suggests the presence of two promoters. In both Ex-1+ and Ex-2+ cDNA clones the next exon is Ex-3, which has a translation-initiating codon. The intron between Ex-3 and Ex-4 is unusually long, about 50 kilobases. Evidence is given that Ex-5, like Ex-6 and Ex-7 (studied previously), is another alternative exon that is selectively programmed, alone or together with Ex-6 or Ex-7 or both, to generate actual or potential Ly-5 isoforms by alternative splicing.

Amplification of suppressor inducer pathway with monoclonal antibody, anti-2H4, identifying a novel epitope of the common leukocyte antigen/T200 antigen

The 2H4 antigen, comprised of a 200/220-kDa glycoprotein of the leukocyte common antigen (LCA) family, is expressed on a suppressor inducer, but not a helper inducer subset of T4 cells. Earlier studies have demonstrated that the T4+2H4+ subset of cells maximally responded to the AMLR and this molecule has an important role in generated suppressor signals in AMLR/Con A-activated T cell systems. In the present study, we examined the effect of a series of monoclonal antibodies including anti-2H4 antibody on the initial activation of T4 cells in response to self-Ia antigens. We found that the addition of anti-2H4 antibody resulted in an augmentation of the proliferative response of T4 cells in AMLR, whereas other antibodies reactive with LCA/T200 antigens lacked this ability. Furthermore, anti-2H4 antibody enhanced both IL-2 production and IL-2R expression in this AMLR system. This enhancing effect was inhibited by anti-T3 antibody. Moreover, the suppressor inducer function of AMLR T4 cells was enhanced with anti-2H4 antibody by increasing the number of 2H4+ cells with high antigen density. Taken together, these results suggest that the 2H4 antigen may serve as an accessory structure for enhancing the activation of the T4+2H4+ suppressor inducer subset at initiation of cell triggering.