Enhancement of the activities of glycosyltransferases involved in the biosynthesis of mucin-type sugar chains in autoimmune MRL lpr/lpr mouse T cells

A distinct CD38+CD45RA+ population of CD4+, CD8+, and double-negative T cells is controlled by FAS

The identification and characterization of rare immune cell populations in humans can be facilitated by their growth advantage in the context of specific genetic diseases. Here, we use autoimmune lymphoproliferative syndrome to identify a population of FAS-controlled TCRαβ⁺ T cells. They include CD4⁺, CD8⁺, and double-negative T cells and can be defined by a CD38⁺CD45RA⁺T-BET⁻ expression pattern. These unconventional T cells are present in healthy individuals, are generated before birth, are enriched in lymphoid tissue, and do not expand during acute viral infection. They are characterized by a unique molecular signature that is unambiguously different from other known T cell differentiation subsets and independent of CD4 or CD8 expression. Functionally, FAS-controlled T cells represent highly proliferative, noncytotoxic T cells with an IL-10 cytokine bias. Mechanistically, regulation of this physiological population is mediated by FAS and CTLA4 signaling, and its survival is enhanced by mTOR and STAT3 signals. Genetic alterations in these pathways result in expansion of FAS-controlled T cells, which can cause significant lymphoproliferative disease.

TcR-alpha/beta(+) CD4(-)CD8(-) T cells in humans with the autoimmune lymphoproliferative syndrome express a novel CD45 isoform that is analogous to murine B220 and represents a marker of altered O-glycan biosynthesis

Autoimmune lymphoproliferative syndrome (ALPS), caused by inherited defects in apoptosis secondary to mutations in genes encoding Fas/CD95/APO-1 and Fas ligand (Fasl)/CD95L, is characterized by nonmalignant lymphadenopathy and splenomegaly, increased T cell receptor alpha/beta(+) CD4(-)CD8(-) T cells (alpha/beta(+) double-negative T cells [alpha/beta(+)-DNT cells]), autoimmunity, hypergammaglobulinemia, and cytokine abnormalities. The alpha/beta(+)-DNT cells are immunophenotypically and functionally similar to alpha/beta(+)-DNT cells that accumulate in lpr and gld mice, which bear genetic mutations in Fas and FasL. In these mice, alpha/beta(+)-DNT cells express the B-cell-specific CD45R isoform B220. We show that alpha/beta(+)-DNT cells of ALPS patients, with either Fas or FasL mutations, also express B220. In addition, also similar to LPR/gLD mice, they have an unusual population of B220-positive CD4(+) T cells. B220 expression, together with our finding of characteristic lectin binding profiles, demonstrates that cell surface O-linked glycoproteins have undergone specific modifications, which may have consequences for lymphocyte trafficking, cell-cell interactions, and access to alternative apoptosis pathways.

Agalactosyl IgG and beta-1,4-galactosyltransferase gene expression in rheumatoid arthritis patients and in the arthritis-prone MRL lpr/lpr mouse

Reduced galactosylation of immunoglobulin G (IgG) is well documented in rheumatoid arthritis (RA), but the reason for this defect is still unknown. There is some evidence supporting a defect in the biosynthetic pathway, and a reduction in the level of beta-1,4-galactosyltransferase (beta-1,4-GalTase) enzyme activity. Since glycosyltransferases are, in general, regulated at the level of transcription, we have measured the level of beta-1,4-GalTase gene expression in B cells from patients with RA and normal control individuals. We found no significant difference in mRNA levels for the transferase in these two groups (P > 0.7). MRL/Mp-lpr/lpr (MRL-lpr) mice develop a spontaneous arthritis with increased levels of agalactosyl IgG (G0). In spite of a significant reduction in the level of beta-1,4-GalTase mRNA in total spleen lymphocytes from MRL-lpr mice compared with the congenic MRL/Mp-(+/+) (MRL-(+/+) mice and with CBA/Ca mice, we found comparable levels of the beta-1,4-GalTase mRNA in purified B cells from both spleen and lymph nodes of the three strains. Amongst the lymphoid compartments examined, the spleen and peripheral blood were found to be the major contributors of G0 in MRL-lpr mice. These data indicate that in neither human RA, nor in an animal model of this disease, is reduced IgG galactosylation caused by impaired expression of the beta-1,4-GalTase gene in B lymphocytes. Furthermore, splenic B cells, which have normal levels of beta-1,4-GalTase mRNA, appear to be a major source of G0 in MRL-lpr mice.

Evaluation of beta 1,4-galactosyltransferase in rheumatoid arthritis and its role in the glycosylation network associated with this disease

Evidence indicating an important link between glycosylation changes and autoimmune rheumatic disease is presented. Attention is especially focused on the interrelationship between reduced galactosylation of the oligosaccharides of IgG, auto-sensitization which is thought to be of central importance in the pathogenesis of rheumatoid arthritis (RA), and the enzyme beta 1,4-galactosyltransferase (GTase) that catalyses the addition of galactose to the oligosaccharide chains on this molecule. Data are presented to indicate that GTase undergoes a variety of normal and disease associated changes. These variations are believed to contribute to the pathological processes in rheumatoid disease, and a hypothesis is suggested, whereby disease is associated with the dysregulation of an integrated glycosylation network, comprising IgG galactosylation, lymphocytic GTase and anti-GTase antibodies, that is a component of the normal immune system.

Beta 1,4-galactosyltransferase variations in rheumatoid arthritis

Evidence indicating an important link between glycosylation changes and autoimmune rheumatic disease is presented. Attention is especially focused on the interrelationship between reduced galactosylation of the oligosaccharides of IgG, auto-sensitization to which is thought to be of central importance in the pathogenesis of rheumatoid arthritis (RA), and the enzyme beta 1,4-Galactosyltransferase (GTase) that catalyses the addition of galactose to the oligosaccharide chains on this molecule. Data are presented to indicate that GTase undergoes a variety of normal and disease associated changes. These variations are believed to contribute to the pathological processes in rheumatoid disease, and a hypothesis is suggested, whereby disease is associated with the dysregulation of an integrated glycosylation network, comprising IgG galactosylation, lymphocytic GTase and anti-GTase antibodies, that is a component of the normal immune system.

Differential B lymphocyte galactosyltransferase activity in the MRL mouse model of rheumatoid arthritis

Oligosaccharides can be of fundamental importance to glycoprotein function. Glycosylation abnormalities are present in rheumatoid arthritis (RA) and may be associated with disease pathogenesis. To determine whether similar disease mechanisms occur in the MRL-1pr/1pr autoimmune arthritic mouse, studies on B lymphocyte galactosyltransferase (GTase) have been carried out. In MRL mice, a significant reduction in peripheral blood lymphocyte (PBL) GTase activity was found when compared to their paired splenic (SP) GTase activity (-69%, p = 0.002) and histocompatible non-autoimmune control CBA/Ca mice (-67%; p = 0.002). The changes in PBL GTase activity are similar to those found in RA and on further analysis, using mixing experiments in the presence of purified human milk GTase, this reduction was shown not to be due to the presence of a soluble intracellular GTase inhibitor. Furthermore when examining MRL derived hybridoma cells producing IgG, significantly reduced GTase activity was detected in the rheumatoid factor (RF) producing hybridoma cells compared to those secreting an irrelevant antibody (-21%, p < 0.05). Together these findings suggest that the glycosylation changes observed in this study, and those reported previously in RA, are tissue-specific, may result from cells trafficking from centres of disease activity and are not the result of direct enzyme inhibition. It is now important to further understand the mechanisms controlling glycosylation and relate disease associated changes with those occurring as part of normal cellular physiology.

Aberrant expression of GM1 on lymph node cells of MRL/Mp-lpr/lpr mice: influences on the autoreactivities of anti-asialo GM1 antibodies

Although changes in surface carbohydrate expression of abnormally expanded MRL/Mp-lpr/lpr (MRL/lpr) lymph node (LN) cells have previously been described, the composition and function of glycolipids present on these cells as well as the spectrum of specificity of anti-carbohydrate antibodies reactive with these cells remains obscure. Analysis of antibodies to a panel of 22 carbohydrate structures using a liposome immune lysis assay (LILA) showed that, except for anti-asialo GM2 (GA2) antibodies, marked reduction of antiglycolipid antibody levels was observed in sera from 4-mo-old MRL/lpr mice compared with these from MRL/Mp(-)+/+ (MRL/+) mice. Absorption experiments revealed that both anti-asialo GM1 (GA1) and globoside antibodies had binding capacity to MRL/lpr LN cells. To elucidate the glycolipid profiles of MRL/lpr LN cells, glycolipids were extracted from LN cells of both MRL/lpr and MRL/+ mice and analysed. A 30-fold elevation of GM1 was found in MRL/lpr LN cells compared with MRL/+ LN cells. From the results of LILA using GA1/GM1 mixed liposomes, aberrantly expressed GM1 inhibited the classical complement pathway but did not interfere with the binding of anti-GA1 antibodies to liposomal GA1. These findings suggest that a drastic GM1 increase on MRL/lpr LN cells would inhibit the action of anti-GA1 antibodies and complement on the cell surface. This may explain the escape of these cells from an activated self directed immune response.

Elevation of the activities of glycosyl transferases involved in polylactosaminoglycan biosynthesis in autoimmune MRL lpr/lpr mouse T cells

Lymph node (LN) T cells from autoimmune MRL/MpJ-lpr/lpr (lpr) mice and control MRL/MpJ-(+)/+ (+/+) mice were compared as to glycosyl transferase activities involved in the biosynthesis of polylactosaminoglycans. The N-acetylglucosaminyl transferase (GlcNAc transferase) activity responsible for the extension of polylactosaminoglycans was assayed. The reaction products with this GlcNAc transferase were characterized by sequential glycosidase treatment and methylation analysis, and the enzyme was found to be classifiable as an UDP-GlcNAc:N-acetyllactosamine beta 1-3 GlcNAc transferase (polylactosamine extension enzyme). The activity of this GlcNAc transferase in T cells from enlarged LN of lpr mice was 3-6 times higher than that in T cells from +/+ mice. On the other hand, activated T cells from +/+ mice only showed about a 2-fold increase in the activity of the transferase, compared with that in resting T cells. B cells from +/+ mice also showed a significantly higher activity of the transferase than +/+ T cells, the enzyme activity being comparable to or slightly lower than that in lpr T cells. Furthermore, when the reaction mixture contained both UDP-GlcNAc and UDP-Gal as donors, extension of the Gal-GlcNAc residue was observed. These results indicated the biosynthetic basis for the abundance of polylactosaminoglycans in lpr T cells and normal B cells. We also found that lpr T cells exhibited significant UDP-GlcNAc:asialo-bovine submaxillary mucin GlcNAc transferase activity. Only weak activity of this enzyme was detected in +/+ resting and activated T cells, and B cells. This enzyme activity suggested the potential for polylactosaminoglycan formation on the mucin-type sugar chains on the surface of lpr T cells.

Two populations of mouse lymphokine-activated killer cells separated by use of soybean agglutinin

We separated lymphokine-activated killer (LAK) cells induced from spleen cells of BALB/c mice by culturing with recombinant interleukin-2 (rIL-2) into soybean agglutinin-positive (SBA+) and soybean agglutinin-negative (SBA-) fractions with a cell sorter at the time when LAK activity reached a maximum (day 3). We found that the cells with LAK activity were enriched in the SBA+ fraction. Analysis of cell surface phenotypes revealed that the SBA+ cells are of non-T cell origin, while the SBA- fraction consists of T cells. We also found that the large granular lymphocyte (LGL) fraction of spleen cells obtained with a Percoll gradient became SBA+ after culture for 3 days with rIL-2, whereas cells of high density did not. The change in SBA binding sites was also examined on C57BL/6 mouse spleen cells and we found that NK1.1+ non-T cells selectively acquire SBA binding sites at an early stage of activation with rIL-2. On the other hand, sorted SBA- cells gradually acquired SBA binding sites on extended culturing with rIL-2. These results suggest that the expression of SBA binding sites is related to the stage of cell activation with rIL-2, though cells of the NK-lineage became SBA+ at an earlier period of a culture with rIL-2 than cells of the T-lineage. Utilizing these findings, we separated NK-derived LAK cells by means of SBA-binding, and used the separated cells for adoptive immunotherapy for experimental pulmonary metastasis. We found that SBA(+)-NK cell-derived LAK cells showed stronger activity for the inhibition of experimental pulmonary metastasis than SBA(-)-T cell-derived LAK cells.

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.