Sialic acid (Sia) is a family of acidic nine-carbon sugars that occupies the nonreducing terminus of glycan chains. Diversity of Sia is achieved by variation in the linkage to the underlying sugar and modification of the Sia molecule. Here we identified Sia-dependent epitope specificity for GL7, a rat monoclonal antibody, to probe germinal centers upon T cell-dependent immunity. GL7 recognizes sialylated glycan(s), the ␣2,6-linked N-acetylneuraminic acid (Neu5Ac) on a lactosamine glycan chain(s), in both Sia modification-and Sia linkage-dependent manners. In mouse germinal center B cells, the expression of the GL7 epitope was upregulated due to the in situ repression of CMP-Neu5Ac hydroxylase (Cmah), the enzyme responsible for Sia modification of Neu5Ac to Neu5Gc. Such Cmah repression caused activation-dependent dynamic reduction of CD22 ligand expression without losing ␣2,6-linked sialylation in germinal centers. The in vivo function of Cmah was analyzed using gene-disrupted mice. Phenotypic analyses showed that Neu5Gc glycan functions as a negative regulator for B-cell activation in assays of T-cell-independent immunization response and splenic B-cell proliferation. Thus, Neu5Gc is required for optimal negative regulation, and the reaction is specifically suppressed in activated B cells, i.e., germinal center B cells.

In the present study, we studied the signal transduction mechanism that is involved in the expression of c-Jun protein evident after exposure of rat liver epithelial RL34 cells to the major end product of oxidized fatty acid metabolism, 4-hydroxy-2-nonenal (HNE). HNE treatment of the cells resulted in depletion of intracellular glutathione (GSH) and in the formation of proteinbound HNE in plasma membrane. In addition, HNE strongly induced intracellular peroxide production, suggesting that HNE exerted oxidative stress on the cells. Potent expression of c-Jun occurred within 30 min of HNE treatment, which was accompanied by a timedependent increase in activator protein-1 (AP-1) DNA binding activity. We found that HNE caused an immediate increase in tyrosine phosphorylation in RL34 cells. In addition, HNE strongly induced phosphorylation of c-Jun N-terminal kinases (JNK) and p38 mitogen-activated protein kinases and also moderately induced phosphorylation of extracellular signal-regulated kinases. The phosphorylation of JNK was accompanied by a rapid and transient increase in JNK and p38 activities, whereas changes in the activity of extracellular signalregulated kinase were scarcely observed. GSH depletion by L-buthionine-S,R-sulfoximine, a specific inhibitor of GSH biosynthesis, only slightly enhanced peroxide production and JNK activation, suggesting that HNE exerted these effects independent of GSH depletion. This and the findings that (i) HNE strongly induced intracellular peroxide production, (ii) HNE-induced JNK activation was inhibited by pretreatment of the cells with a thiol antioxidant, N-acetylcysteine, and (iii) H 2 O 2 significantly activated JNK support the hypothesis that pro-oxidants play a crucial role in the HNE-induced activation of stress signaling pathways. In addition, we found that, among the inhibitors of tyrosine kinases, cyclooxygenase, and Ca 2؉ influx, only quercetin exerted a significant inhibitory effect on HNE-induced JNK activation. In light of the JNK-dependent induction of c-jun transcription and the AP-1-induced transcription of xenobiotic-metabolizing enzymes, these data may show a potential critical role for JNK in the induction of a cellular defense program against toxic products generated from lipid peroxidation.

The ability of Bacteroides gingivalis 381 to attach to hydroxyapatite (HA) beads, treated with either human type I or type IV collagen, or to particles of bovine bone collagen was studied. All preparations were blocked with human albumin prior to being incubated with 3H-thymidine-labeled B. gingivalis 381 cells. The presence of collagen on HA surfaces (C-HA) significantly promoted attachment of the organism. HA treated with Type IV collagen bound B. gingivalis cells more effectively than did HA treated with type I collagen. Attachment of two additional strains of B. gingivalis to HA was also promoted by collagen. Binding to type I or type IV C-HA occurred rapidly, and equilibrium was attained within 45 min. B. gingivalis 381 cells also bound to particles of bovine bone collagen, and this appeared to be biphasic. Heating the bacteria abolished their ability to bind to C-HA. Attachment of B. gingivalis 381 cells to HA treated with type I collagen was strongly inhibited by the presence of soluble type I or type IV collagen, or gelatin, but not by the presence of human albumin, salivary proline-rich protein 1, or saliva. Human serum, fibronectin, fibrinogen, certain protease inhibitors, and some peptides were also inhibitory. 3H-fibronectin bound to bovine bone collagen particles and blocked the attachment of 14C-B. gingivalis cells. Mild trypsin treatment of the fibronectin-collagen complex restored its ability to promote 14C-B. gingivalis attachment concomitant with the loss of 3H-fibronectin. We suggest that elevated levels of proteases in the gingival sulcus, such as are associated with poor oral hygiene and gingivitis, might remove fibronectin and expose collagen molecules in the basement membrane, thereby promoting the attachment of B. gingivalis cells and facilitating their invasion into gingival tissues.

Although the induction of glutathione S-transferase (GST) activity by tert-butylhydroquinone (tBHQ) has been well-documented in several cell culture systems and rodent experiments, the exact mechanism responsible for its inducibility is still not thoroughly understood. To more precisely define the molecular mechanism of GST induction by tBHQ, we examined the one-electron oxidation and glutathione (GSH) reaction potentials of tBHQ as compared to its analogue, 2,5-di-tert-butylhydroquinone (DtBHQ). tBHQ and DtBHQ showed similar one-electron oxidation potentials, including free radical quenching (antioxidant), oxidative conversion of both compounds to a benzoquinone form, and Cu(2+)-dependent superoxide generation. On the other hand, the reduced GSH level was observed by the addition of tBHQ, but not DtBHQ, suggesting that tBHQ acts as an electrophile while DtBHQ does not. The data were consistent with the observation that tBHQ more potently induced the GSTP1 gene expression in RL34 cells than DtBHQ did. Moreover, we indeed detected the GSH-tBHQ conjugates in the cells exposed to tBHQ using an electrochemical detector-high-performance liquid chromatography technique. Thus, we conclude that an electrophilic quinone oxidation product that reacts with intracellular nucleophiles including protein thiol or GSH plays a major role in the GSTP1 gene expression.

To understand physiological roles of tissue mast cells, we established a culture system where bone marrow-derived immature mast cells differentiate into the connective tissue-type mast cell (CTMC)-like cells through modifying the previous co-culture system with Swiss 3T3 fibroblasts. Our system was found to reproducibly mimic the differentiation of CTMCs on the basis of several criteria, such as granule maturation and sensitivity to cationic secretagogues. The gene expression profile obtained by the microarray analyses was found to reflect many aspects of the differentiation. Our system is thus helpful to gain deeper insights into terminal differentiation of CTMCs.

The hemagglutinating factor (hemagglutinin) of Bacteroides gingivalis was prepared from the supernatant of a 5-day diffusate broth culture by ammonium sulfate precipitation and column chromatography with a hydrophobic column of Phenyl-Sepharose CL-4B, DEAE-Sephadex A-50, and Sephadex G-100 gel filtration. The hemagglutinating activity of the preparation was 53.3 times higher than that of ammonium sulfate precipitate. In electron microphotographs, hemagglutinin appears to have a vesicle or tubelike structure. The hemagglutinating activity of intact cells was completely destroyed by heating at 100°C for 10 min, but the activity of extracted hemagglutinin was heat stable. The activity of hemagglutinin was inhibited by L-arginine and L-lysine and partially inhibited by phospholipase D, but it was not affected by proteolytic enzymes, neuraminidase, hyaluronidase, lipase, phospholipase A and C, or sugars. The B. gingivalis hemagglutinin appeared to be comprised mainly of a 40,000-molecular-weight material. The Fab fragment of immunoglobulin G prepared from rabbit antiserum to whole cells of B. gingivalis and monoclonal antibody against the hemagglutinin bound to the cell surface and inhibited the hemagglutinating activity of both the cells and the purffied hemagglutinin.

Serum and gingival crevicular fluid from normal healthy adults and patients with periodontitis were screened for immunoglobulin G antibodies to antigens from Bacteroides gingivalis 381, Bacteroides intermedius 24, Bacteroides loescheii ATCC 15930, Fusobacterium nucleatum ATCC 25586, Eikenella corrodens 1073, Actinobacillus actinomycetemcomitans ATCC 29522, and Capnocytophaga sp. strain M-12. Immunoglobulin G antibody titers to the antigens were measured by an enzyme-linked immunosorbent assay. The antibody levels to B. gingivalis in serum and gingival crevicular fluid were significantly higher in the samples from patients with periodontitis than in samples from healthy individuals. Although there were individual differences within patient groups, a positive correlation (P < 0.01) was found between the serum immunoglobulin G levels to B. gingivalis and the development of periodontitis. The antibodies to F. nucleatum (P < 0.05), E. corrodens (P < 0.05), and A. actinomycetemcomitans were slightly higher in patients with periodontitis than in normal subjects. There were no remarkable differences between the two groups in titers to B. intermedius, B. Ioescheii, and Capnocytophaga sp.

The relationship between the serum IgG antibody titer against seven species of Gram-negative periodontopathic bacteria and clinical parameters (including plaque index, gingival index, periodontal pocket depth, and alveolar bone loss) was studied in 38 subjects. IgG antibody titer against the sonicated antigens was determined by micro-ELISA. A statistically significant correlation was found between the serum antibody titer against B. gingivalis and the degree of clinical parameters, especially pocket depth. The serum IgG levels against the seven micro-organisms in 16 periodontal patients before and after clinical treatment were also determined. Responses to B. gingivalis decreased (p less than 0.001), whereas responses to E. corrodens (p less than 0.01) increased slightly. No marked differences were noted between pre- and post-treatment sera in titers against B. intermedius, B. loescheii, F. nucleatum, A. actinomycetemcomitans, and C. ochracea.