A gene (Neu-1) on chromosome 17 of the mouse affects acid alpha-glucosidase and codes for neuraminidase

The ST3Gal-I sialyltransferase controls CD8+ T lymphocyte homeostasis by modulating O-glycan biosynthesis

T lymphocyte activation evokes distinct changes in cell surface O-glycans. CD8+ T cells undergo an elimination of sialic acid on core 1 O-glycans and an induction of core 2 O-glycans until either apoptotic death or differentiation into memory cells. We find that the ST3Gal-I sialyltransferase is required for core 1 O-glycan sialylation and its deficiency induces core 2 O-glycan biosynthesis. Apoptosis ensues with the loss of peripheral CD8+ T cells in the absence of immune stimulation. Cell surface ligation of the ST3Gal-I substrate CD43 recapitulates this phenotype by a caspase 3-independent mechanism. Control of core 1 O-glycan sialylation in T lymphocytes by ST3Gal-I comprises a homeostatic mechanism that eliminates CD8+ T cells by apoptosis while facilitating the production of viable CD8+ memory T cells.

Influenza virus neuraminidase alters allogeneic T cell proliferation

Influenza virus elicits good cellular and humoral immune responses. Unlike the cytotoxic T lymphocyte response to many other antigens, the cytotoxic T lymphocyte response to influenza virus is CD4(+) T cell independent, suggesting that viral infection of antigen-presenting cells may alter their capacity to stimulate T cell responses. To clarify the role of influenza virus in these functional alterations, we compared T cell responses to uninfected and A/PR/8/34-infected dendritic cells (DC). DC were prepared from the bone marrow of C57BL/6 (H2(b)) mice and used to stimulate in vivo and in vitro alloreactive T cell responses. In both cases, influenza virus infection increased the capacity of DC to stimulate T cell proliferation. This enhancement was blocked by antibodies specific for neuraminidase (NA), but not hemagglutinin. Infection was not required to observe enhanced T cell proliferation, showing that NA from exogeneous virus particles can facilitate this effect. These results are the first to show that influenza virus alters the capacity of DC to stimulate T cell proliferation through mechanisms mediated by viral NA.

Identification of a sialidase encoded in the human major histocompatibility complex

Mammalian sialidases are important in modulating the sialic acid content of cell-surface and intracellular glycoproteins. However, the full extent of this enzyme family and the physical and biochemical properties of its individual members are unclear. We have identified a novel gene, G9, in the human major histocompatibility complex (MHC), that encodes a 415-amino acid protein sharing 21-28% sequence identity with the bacterial sialidases and containing three copies of the Asp-block motif characteristic of these enzymes. The level of sequence identity between human G9 and a cytosolic sialidase identified in rat and hamster (28-29%) is much less than would be expected for analogous proteins in these species, suggesting that G9 is distinct from the cytosolic enzyme. Expression of G9 in insect cells has confirmed that it encodes a sialidase, which shows optimal activity at pH 4.6, but appears to have limited substrate specificity. The G9 protein carries an N-terminal signal sequence and immunofluorescence staining of COS7 cells expressing recombinant G9 shows localization of this sialidase exclusively to the endoplasmic reticulum. The location of the G9 gene, within the human MHC, corresponds to that of the murine Neu-1 locus, suggesting that these are analogous genes. One of the functions attributed to Neu-1 is the up-regulation of sialidase activity during T cell activation.

PFGE mapping and RFLP analysis of the S/D region of the mouse H-2 complex

We have constructed a long range restriction map of the S/D segment of the mouse H-2 complex by pulsed field gel electrophoresis and hybridization with mouse cDNA probes to Bf and Tnfa genes and human cDNA probes to BAT2, BAT3, BAT4, BAT5, and BAT6 genes which have recently been mapped to the human HLA complex between C2 and HLA-B. The distance between the mouse C2 and Tnfa genes was found to be approximately 350 kilobases. The position of the mouse Bat genes in this map were found to be comparable to the position of the BAT genes in the human HLA complex. A panel of recombinant mouse strains was also examined by restriction fragment analysis with probes detecting the Hsp70, Bat5, and Tnfa genes. The results indicate that recombination in this segment is not random. No recombinants were found with crossovers between the C2 and Hsp70 genes and only one recombinant was found with a crossover between Tnfa and H-2D. In contrast, the crossover sites of 16 recombinants were mapped between the Hsp70 and Tnfa genes. Seven of these recombinants were found to have crossovers between Hsp70 and Bat5 and three recombinants were found to have crossover sites between Bat5 and Tnfa.

Distorter genes of the mouse t-complex impair male fertility when heterozygous

Male mice heterozygous for two distorter genes,Tcd-1andTcd-2, of the mouset-complex but homozygous wild type for the responder, were generated by crossing animals carrying the partialt-haplotypesth51andth18to inbred strains. The fertility of these males was then compared with that of their brothers carrying normal chromosome 17s. On three of the inbred backgrounds used, C3H/HeH, C57BL/6J and TFH/H, theth51th18+ / + + + males were significantly less fertile than their normal sibs. With the fourth inbred strain used, SM/JH, both types of male were nonnally fertile. This confirmed earlier preliminary findings that when both homologues of chromosome 17 carry wild-type alleles of the responder, heterozygosity for the distorter genes is sufficient to impair fertility, but the effect varies with genetic background. These results are consistent with the concept that both the transmission ratio distortion and the male sterility caused by thet-complex are due to harmful effects of the distorter genes on wild-type alleles of the responder.

Electrophoretic analysis of liver neuraminidase-1 variation in mice and additional evidence concerning the location of NEU-1

Neuraminidase-1 (NEU-1) is one of two neuraminidase isozymes which can be detected electrophoretically in mouse liver extracts. The inheritance of variation in NEU-1 and the linkage relationships of the gene controlling this variation were studied through a backcross analysis involving the SM/J and MA/MyJ inbred strains, and by examination of NEU-1 phenotypes in three congenic strains: B10.SM, B10.SM(22R) and B10.RVB. The data indicate that NEU-1 is controlled by Neu-1, a gene previously identified by its effect on total liver neuraminidase activity in whole tissue homogenates. Analysis of the congenic strains revealed identical low activity (SM/J-type: Neu-1a/Neu-1a) NEU-1 phenotypes in all three strains. This indicates that Neu-1 lies in the segment of the SM/J-derived H-2 region that is common to all three strains: H-2E alpha to H-2D. In addition, we examined the relationship between NEU-1 and phenotypic variation in liver acid phosphatase (AP; for which a new typing method is described) and linkage order among several other enzyme-coding genes linked to H-2. In all animals that could be scored confidently for AP, the NEU-1 and AP phenotypes were concordant, adding support to the hypothesis that both phenotypes are controlled by Neu-1. Recombination rates among six H-2-linked marker loci were unexpectedly low, but were sufficient to verify the position of Upg-1 as the telomeric flanking marker relative to Glo-1, H-2 (C4), Neu-1 (Apl), Ce-2 and Pgk-2.

Activation of T lymphocytes results in an increase in H-2-encoded neuraminidase

The endogenous neuraminidase activity of various mouse lymphoid subpopulations and tissue compartments was examined by a sensitive fluorometric assay. These analyses indicated that activated T lymphocytes possessed a significantly higher level of intracellular neuraminidase than activated B or resting T or B lymphocytes. Examination of the level of neuraminidase in bone marrow, thymus, lymph node, and unfractionated spleen indicated that these lymphoid tissues contained significantly less neuraminidase than was detected in stimulated T cells. Kinetic studies revealed that the majority of the increase in neuraminidase activity occurred between 24 and 48 h following stimulation. Analysis of activated T lymphocytes prepared from a panel of inbred mouse strains indicated that cells from mice of the H-2v haplotype, which possess the Neu-1a allele and are deficient in liver neuraminidase, exhibited a level of activity which was significantly lower than that detected in stimulated T cells from other mouse strains. These results indicate that the endogenous neuraminidase activity of T lymphocytes increases upon stimulation, and that the level of this enzyme activity in lymphoid cells is also controlled by the Neu-1 locus, which is located in the H-2 region of the major histocompatibility complex.

The role of lysosomal sialidase and beta-galactosidase in processing the complex carbohydrate chains on lysosomal enzymes and possibly other glycoproteins

Previous studies using the lectin RCA-I from Ricinus communis have indicated that several lysosomal enzymes in the fibroblasts of patients deficient in beta-galactosidase carry excess terminal galactose. Electrophoretic studies have shown that the same enzymes and the non-lysosomal adenosine deaminase also show excess terminal sialic acid in patients deficient in sialidase. In this paper we confirm, using Jack-bean beta-galactosidase, that the binding to RCA-I of the purified N-acetyl-beta-D-hexosaminidase from a patient with GM1 gangliosidosis depends on a terminal beta-linked galactose. We provide evidence, using bacterial sialidase and measuring the binding to RCA-I, for excess subterminal galactose on the enzymes of patients deficient in sialidase. We also show that adenosine deaminase from the fibroblasts of patients deficient in beta-galactosidase has increased binding to RCA-I. These observations suggest that in healthy individuals the carbohydrate structure of the precursors of lysosomal enzymes and possibly some other glycoproteins also includes extended carbohydrate side chains with terminal sialic acid and subterminal galactose, and that the mature enzyme extracted from tissues is the product of degradation.