In vivo induction of apoptosis and immune responses in mice by administration of lipopolysaccharide from Porphyromonas gingivalis

In vivo administration of Porphyromonas gingivalis lipopolysaccharide (Pg-LPS) to mice induced apoptosis before a specific immune response. Apoptosis was associated with the expression of immunoglobulin and Ia on B cells and of CD5 and several markers on T cells. Apoptosis peaked in the spleen and lymph nodes on day 2, and the second peak occurred in the thymus on day 9. Tumor necrosis factor alpha (TNF-alpha) could mediate apoptosis, because the serum TNF-alpha levels were significantly higher than those of controls at 1 day before apoptosis and recombinant murine TNF-alpha induced apoptosis. The apoptosis induced by Pg-LPS was similar to that induced by Escherichia coli LPS in its basic manner, but it was unique in the response of thymus T cells. It was suggested that Pg-LPS could induce apoptosis for the elimination of early nonspecific activated lymphocytes.

Alcohol and substance use among Japanese high school students

In the first large-scale survey on the use of alcohol and tobacco and the inhalation of paint thinner by Japanese high school students, a higher percentage of respondents reported past or regular use of these substances than in a 1978 survey. The survey was conducted in 44 high schools. The 14,438 respondents (ages 15-18 years) represented 9 of Japan's 47 geographically distinct urban and rural prefectures. Most (76%) reported that they had consumed alcohol at some time, and 50% reported drinking on a regular basis. Alcohol consumption, drinking partners, and motivation for drinking were compared by student gender, geographic region, and years of education. Fewer students reported smoking cigarettes: 32% had smoked at some time, and 14% smoked regularly. Inhalation of paint thinner was rare: 3% had purposely inhaled it, and 1% had abused it. A significant percentage of the alcohol drinkers also used tobacco and/or thinner, a tendency that was the same despite differences in gender, grade in high school, and urban or rural geographic region. A tendency toward polysubstance use was evident among these high school students.

[Cancer detection with whole-body FDG PET images without attenuation correction]

Whole-body positron emission tomography (PET) using 2-deoxy-2-[18F]fluoro-D-glucose (FDG) has been applied successfully for the detection of cancer. In PET studies, transmission scans for attenuation correction are usually performed. In whole-body PET studies, however, the transmission scans lengthen the acquisition time and are not practical for routine clinical use. Thirty-two patients underwent whole-body PET studies with transmission scans. A total of 106 lesions were true positive on corrected images. At the same time that the corrected images were being reconstructed, uncorrected images were also reconstructed and visually inspected. In a patient with a large breast cancer (11 cm in diameter), the parasternal metastatic lymph node was not identified on the uncorrected image because of image artifacts produced by high FDG accumulation in the breast cancer. In a patient with recurrent colonic cancer, paraaortic metastatic lymph nodes were not well visualized because of attenuation effects. However, 104 out of 106 (98.1%) lesions were recognizable on uncorrected images as well as corrected images. This suggests that uncorrected images can be used for the detection of cancers.

Purification and substrate specificity of an endo-beta-N-acetylglucosaminidase from pea (Pisum sativum) seeds

An endo-beta-N-acetylglucosaminidase was purified to homogeneity from the seeds of pea (Pisum sativum). The molecular mass of the purified enzyme was estimated to be 41,669 Da by MALDI-TOF MS analysis and its isoelectric point to be 4.3 by isoelectric focusing. The enzyme was stable at pH 4-7 and at 25-50 degrees C, and had the highest activity toward Man6GlcNAc2-PA at pH around 7.0. Oligomannose type sugar chains (Man9-6GlcNAc2-PA) and a hybrid type sugar chain (GlcNAc1Man5GlcNAc2-PA) were most favored substrates followed by Man5GlcNAc2-PA, Man3GlcNAc2-PA, and GlcNAc2Man3GlcNAc2-PA, but xylose-containing sugar chains (Man4-3Xyl1GlcNAc2-PA and Man3Fuc1Xyl1GlcNAc2-PA) or a biantennary complex type sugar chain (Gal2GlcNAc2Man3GlcNAc2-PA) could not be hydrolyzed by the enzyme. The Km values of the enzyme for Man5GlcNAc2-PA, Man6GlcNAc2-PA, and Man9GlcNAc2-PA were 0.40 mM, 0.25 mM, and 0.32 mM, respectively.

[Retrospective analysis on 21 patients with follicular lymphoma]

We retrospectively analyzed the clinical data of the 21 patients with follicular lymphoma admitted to our institution from 1977 to 1994. The frequency of follicular lymphoma was 9.1% in the 231 patients with non-Hodgkin's lymphoma. Overall survival rates at 1 year, 3 years, and 5 years were 90.2%, 78.2%, and 52.1%, respectively. The median follow-up of surviving patients and time to treatment failure (TTF) was 43 months and 30 months, respectively. The median time from disease progression to death was 171 days. In univariate analysis, factors associated with poor survival were stage IV (Ann Arbor staging system), anemia (hemoglobin level less than 10g/dl), bone marrow involvement, two or more extranodal sites, and failure in induction of complete remission (CR) in the entire course. Factors associated with short TTF were anemia, bone marrow involvement, and failure in induction of CR. In multivariate analysis, induction of CR affected survival and TTF independently.

Developmentally regulated expression of a cell surface protein, neuropilin, in the mouse nervous system

Neuropilin (previously A5) is a cell surface glycoprotein that was originally identified in Xenopus tadpole nervous tissues. In Xenopus, neuropilin is expressed on both the presynaptic and postsynaptic elements in the visual and general somatic sensory systems, suggesting a role in neuronal cell recognition. In this study, we identified a mouse homologue of neuropilin and examined its expression in developing mouse nervous tissues. cDNA cloning and sequencing revealed that the primary structure of the mouse neuropilin was highly similar to that of Xenopus and that the extracellular segment of the molecule possessed several motifs that were expected to be involved in cell-cell interaction. Immunohistochemistry and in situ hybridization analyses in mice indicated that the expression of neuropilin was restricted to particular neuron circuits. Neuropilin protein was localized on axons but not on the somata of neurons. The expression of neuropilin persisted through the time when axons were actively growing to form neuronal connections. These observations suggest that neuropilin is involved in growth, fasciculation, and targeting for a particular groups of axons.

A case of uveitis associated with chronic active Epstein-Barr virus infection

Ocular complications of chronic active Epstein-Barr virus infection (CAEBV) have rarely been reported. We describe a 7-year-old girl with CAEBV with associated uveitis. The patient was first observed to have recurrent fever and hepatosplenomegaly in August 1991. She presented with left facial nerve palsy in June 1993. Ocular examination showed right iridocyclitis. Both optic disks were swollen, and the retinal vessels were dilated. Antibody titers to EBV were markedly elevated. Treatment with topical steroids. systemic interleukin-2 and splenectomy dramatically relieved all her symptoms. including the ocular ones.

Polymeric calcium phosphate cements derived from poly(methyl vinyl ether-maleic acid)

OBJECTIVES

The purpose of this study was to assess the feasibility of forming polymeric calcium phosphate cements from a mixed powder of dicalcium phosphate/tetracalcium phosphate or only tetracalcium phosphate and poly(methyl vinyl ether-maleic acid) (PMVE-Ma), and to study their setting reaction.

METHODS

The setting reaction process of the polymeric cements was evaluated by mechanical strength tests, infrared spectroscopy and x-ray diffraction analysis and compared with that of a water-setting calcium phosphate cement. The mechanical strength data were analyzed using ANOVA and Scheffé's multiple comparisons test.

RESULTS

Cements prepared from the mixed powder and 25-30 wt% aqueous solutions of PMVE-Ma had high mechanical strength after 24 h storage in distilled water at 37 degrees C. The hardening mechanism depended on an acid-base reaction between the carboxyl groups of PMVE-Ma and the mixed powder, especially its tetracalcium phosphate component. The formation of hydroxyapatite in the polymeric calcium phosphate cement was not detected and is apparently inhibited as a result of the competing reaction of PMVE-Ma with the mixed powder.

SIGNIFICANCE

The cement-forming reaction was significantly faster than that of a water-setting calcium phosphate cement and slower than that observed with the mixed powder and polyacids such as poly(acrylic acid). The characteristics of the polymeric cements suggest that the materials may be useful in cavity lining or endodontic sealing.

Effect of mutations on the intracellular localization of Bombyx mori cytoplasmic polyhedrosis virus polyhedrin

We have already cloned the polyhedrin genes of the wild-type strain H Bombyx mori cytoplasmic polyhedrosis virus (BmCPV) and its mutant, strain A. In this work, polyhedrin genes of mutant BmCPV strains C1 and C2 were cloned and their nucleotide sequences were determined. The polyhedrin amino acid sequences of strains C1 and C2 were compared with that of strain H. Strains C1 and C2 contained two and three sites of mutation in their polyhedrin genes, respectively. Four amino acids (249RLLV) were added at the carboxy terminus of the polyhedrin of strain A, C1 and C2 and the corresponding polyhedrin genes were introduced into a baculovirus expression vector. Intracellular localization of expressed polyhedrin as well as the morphology and localization of polyhedra were investigated by Western blot and microscopy analysis. Recombinant baculovirus containing the polyhedrin gene of strain H produced hexahedral polyhedra in both the cytoplasm and the nucleus. However, the hexahedral polyhedra of strain A were localized only in the nucleus. Normal polyhedra were not observed in cells infected with recombinant baculoviruses expressing strain C1 or C2 polyhedrin genes, but amorphous structures were found in infected cells. Results of expression of a chimaeric luciferase-containing carboxyl-terminal sequence of strain A demonstrated that this sequence was responsible for the nuclear localization. We suggest that a mutation at the carboxy terminus of BmCPV polyhedrin led to nuclear localization of polyhedrin and that several other mutations were responsible for modification of the crystallization pattern of polyhedrin.

[New concepts on precancerous lesions of the stomach]

As for precancerous lesion of the stomach detail analysis of endoscopic follow-up cases and histopathological investigations brought some new informations on its carcinogenesis. In this paper recent several reports were introduced and discussed on new opinion of precancerous conditions such as adenoma, intestinal metaplasia, gastric ulcer, remnant stomach and H. pylori. Gastric adenoma was considered to be neoplastic because of high incidence of carcinoma in situ. The stomach coexisted with adenoma showed high percentage of new arising tumor in same stomach and therefore, we can say that these are thought to be high risk group for well differentiated adenocarcinoma. Concerning the relation between intestinal metaplasia and gastric cancer we have never obtained final conclusion. However, it is likely that incomplete type of intestinal metaplasia appeared to be coexistent with gastric cancer, especially intestinal type carcinoma, which was thought to be paracancerous lesions. Recent advance of molecular biology has indicated new knowledge on gastric carcinogenesis, suggestive of multistep pathways. According to their reports, genomic instanbility appeared frequently in gastric adenoma and intestinal metaplasia as well as gastric carcinoma. Gastric carcinogenesis for ulcer, remnant stomach and H. pylori was also discussed. In near future the mechanism of gastric carcinogenesis is expected to be solved from view point of genetic events.

Three novel mutations in the interleukin-2 receptor gamma chain gene in four Japanese patients with X-linked severe combined immunodeficiency

Three novel mutations in the IL-2R gamma chain gene were identified in four Japanese patients with X-linked severe combined immunodeficiency by direct sequence analysis of polymerase chain reaction (PCR) amplified DNA fragments.

Cyanamide-associated alcoholic liver disease: a sequential histological evaluation

This is the first study that we are aware of that followed the histopathological progression of the liver disease that was caused by the combination of both chronic alcohol use and cyanamide, an antidipsotropic agent. Two sequential liver biopsy specimens were obtained on 29 alcoholics who relapsed with varying histories of cyanamide treatment. Cyanamide induced ground-glass inclusions (GGIs) in the hepatocytes. Two groups were identified, depending on whether GGIs proliferated or regressed, which was, in turn, found contingent on the duration of cyanamide treatment and the drug-free period. Group 1 included 14 cases in which GGIs either emerged only in the second biopsy specimen or else were increased in the second specimen as compared in the initial specimen. Group 2 composed of 15 cases in which GGIs were either not observed in either specimen or decreased in the second specimen as compared in the initial specimen. Acidophilic bodies were sequentially increased in five cases (36%) of group 1 and in none of group 2. The severity of portal inflammation worsened in 10 cases (71%) of group 1 but in 2 cases (13%) of group 2, although the changes in fibrotic process did not differ between two groups. These differences could not be explained on the basis of the daily ethanol consumption and the length of relapses of the two groups. Thus, when cyanamide-treated alcoholics relapsed, the combined effect of cyanamide and alcohol produced the development of acidophilic bodies and portal inflammation along with the emergence of GGIs.

[MR imaging findings of the femoral marrow in myelodysplastic syndrome]

MR imaging of the femoral marrow was performed in 30 patients with myelodysplastic syndrome (MDS), 11 cases of which evolved to acute myeloid leukemia (AML). The MRI appearance was classified into five patterns: 1) fatty marrow; 2) faint signal; 3) nodular pattern; 4) heterogeneous infiltration; and 5) diffuse infiltration. For each type of MDS, MRI patterns of the femoral marrow were evaluated and compared with those in normal subjects as well as in patients with aplastic anemia. Signal intensity alteration, a low signal on T1-weighted SE image and a high signal on STIR image, began in the proximal femoral marrow almost symmetrically in patients with MDS. The area of abnormal signal intensity tended to gradually extend towards the distal portion of the femur as the disease progressed. MRI patterns of the femoral marrow correlated with marrow cellularity, and diffuse marrow infiltration was noted in patients with a more advanced type of MDS or with severe anemia. There were limitations to making an accurate diagnosis of the MDS type on the basis of the MRI pattern. Progression of the MRI appearance in the course of MDS was thought to be a sign suggesting evolution to AML. It was difficult to differentiate hypoplastic MDS from aplastic anemia, although the nodular pattern was commonly seen in the latter disease.

Splenectomy before tumor inoculation prolongs the survival time of cachectic mice

The effects of splenectomy on the development of cachexia, tumor growth and animal survival were studied in tumor-bearing CDF1 mice. Mice were inoculated with two subclones of colon 26 adenocarcinoma, clone 20 (with a potent capacity to induce cachexia) and clone 5 (without such activity), and underwent splenectomy before or after tumor inoculation. Splenectomy significantly prolonged the survival of mice bearing clone 20 when it was performed prior to tumor inoculation, although the progression of cachexia and tumor growth were not affected. The survival rate was higher in splenectomized than it was in nonsplenectomized mice 20-40 days after tumor inoculation. Such effects on survival were not observed, however, in mice splenectomized after inoculation with clone 20 or in mice that underwent splenectomy either before or after inoculation with clone 5. The decrease of peripheral blood lymphocyte count observed in mice bearing clone 20 was magnified when splenectomy was performed before tumor inoculation, but the serum levels of tumor necrosis factor and interleukin-6 were comparable. These results indicate that cancer death from cachexia is not directly attributable to enhanced catabolism. The mechanism by which splenectomy ameliorates the survival of cachectic mice remains to be studied, although several changes observed in the splenectomized mice after inoculation, including decreases in the peripheral blood L3T4+ cells and Lyt-2+ cells on the 9th day and 15th day respectively, and increase in the L3T4+/Lyt-2+ cell ratio on the 15th day suggest the involvement of the modified host's immune response.

Alcohol and aldehyde dehydrogenase polymorphisms and the risk for alcoholism

OBJECTIVE

The authors studied a large number of Japanese alcoholic patients and comparison subjects to establish the genotype frequencies of alcohol dehydrogenase-2 (ADH2) and mitochondrial aldehyde dehydrogenase (ALDH2) and to quantify the relative risk for alcoholism from the results.

METHOD

The subjects were 655 alcoholic patients and 461 comparison subjects. ADH2 and ALDH2 were genotyped by the combination of polymerase chain reaction and hybridization methods.

RESULTS

Active ALDH2 and usual ADH2 were significantly more frequent in the alcoholic patients. Inactive ALDH2 was not always associated with a low risk of alcoholism, and active ALDH2 was not always associated with high risk. In individuals with heterozygous inactive ALDH2 and usual ADH2, the odds ratio for alcoholism was high.

CONCLUSIONS

The risk for alcoholism in Japanese has been accurately estimated on the basis of the genotype frequencies of ADH2 and ALDH2. Many Japanese may be protected from alcoholism by inactive ALDH2 and by higher frequencies of atypical ADH2.

[Endoscopic mucosal resection of the stomach using a ligating device (EMRL)--experimental study for the purpose of establishing reliable and safe technique]

We confirmed a new reliable and safe technique for endoscopic mucosal resection of the stomach using a ligating device (EMRL), which was used for endoscopic ligation of esophageal varices. We resected the gastric mucosa by this procedure in 6 mongrel dogs, and examined resected specimens histopathologically. It is concluded that EMRL can take a mucosal specimen 15 x 12mm in size on the average, be performed almost all the site which was previously difficult to resect endoscopically, and the submucosal local injection of physiological saline solution is necessary to perform EMRL. Based on these conclusion, we experimented to establish the safe and reliable technique of the divided mucosal resection, too. EMRL procedure is an easy and valuable treatment modality.

Collaborative work to determine an optimal administration period and optimal parameters for detection of effects on male fertility in rats--male reproductive toxicity study of haloperidol

Haloperidol, a neuroleptic, was orally administered at 0, 3, 10, 30 and 60 mg/kg/day in a 4-week dosing study, and 0, 3, 10 and 30 mg/kg/day in a 9-week dosing study, to Sprague-Dawley male rats which were then sacrificed for histopathological examination or mated with untreated females. The males in the mating groups were continuously treated during the mating period. Sperm positive females were sacrificed on day 20 of gestation. The males in the histopathology groups were sacrificed after 4- or 9-week dosing and their testes were fixed in Bouin's fluid and sections stained with HE or PAS. The mated males were sacrificed and reproductive organ weights were determined. At 3 mg/kg or more, reduced spontaneous motor activity was observed and body weights were lowered. The absolute weight of testes was decreased with 60 mg/kg in the 4-week dosing study, and was decreased with 10 and 30 mg/kg in the 9-week dosing study. However, the relative weight was increased or showed a tendency to increase. In the 4-week dosing study, decrease in the fertility index with 60 mg/kg and increase in pre-implantation loss with 30 mg/kg or more were noted. However, there were no adverse effects on the copulation index in any of the treated groups. The males given 60 mg/kg showed slight changes in the testes (necrosis of pachytene spermatocytes in seminiferous tubules of stage VII, exfoliation of round spermatids in the lumina and atrophy of Leydig cells) and seminal vesicles (atrophy of epithelial cells). Atrophy of Leydig cells was also observed at 30 mg/kg in the 4-week dosing study. In the 9-week dosing study, neither male reproductive ability nor histopathological parameters were affected by haloperidol up to 30 mg/kg. From the results detailed above, it may be concluded that 4-weeks dosing before mating is suitable for detection of effects of haloperidol on male reproductive ability, and that histopathological changes together provide an optimal parameter for predicting male reproductive disorders.

Effects of an HMG-CoA reductase inhibitor on cytokine production by human monocytes/macrophages

It has been reported that the HMG-CoA reductase inhibitor simvastatin does not always effectively lower plasma LDL. This drug acts to monocytes/macrophages directly and inhibits cholesterol ester accumulation in these cells. However cytokine production in macrophages when simvastatin was administrated has not been described. In this study, we examined whether simvastatin affects cytokine production in human monocyte-derived macrophages. Simvastatin at doses ranging from 10(-9) to 10(-5) M did not affect the synthesis of proinflammatory cytokines (IL-1 beta, IL-6, IL-8) from human peripheral mononuclear cells. In addition, any changes in cytokine-induced cytokine production (IL-1-induced IL-8 synthesis) were not detected after the addition of simvastatin. The present results suggest that simvastatin suppresses foam cell formation in monocyte/macrophage, without affecting the immunological or inflammatory functions of these cells.

The pathophysiological roles of heterogeneous eosinophils in allergic rhinitis caused by house dust mites

We examined the biological characteristics of normodense and hypodense eosinophils prepared from the peripheral blood of the patients with allergic rhinitis caused by house dust mites by measuring leukotriene C4 (LTC4), platelet-activating factor (PAF), and superoxide anions. The normodense (density: 1.100-1.095) and the hypodense (density: 1.080-1.070) eosinophils were prepared by a Percoll density gradient. The normodense eosinophils produced a greater amount of LTC4 (15 ng/10(6) cells) after stimulation by calcium ionophore A23187 than the hypodense eosinophils (1.8 ng/10(6) cells). On the other hand, in the hypodense eosinophils higher amounts of both PAF (5210 pg/10(7) cells/15 min) and superoxide anions (0.33 nmoles/10(7) cells/min) were produced by calcium ionophore A23187 than in the normodense eosinophils, 501 pg/10(7) cells/15 min and 0.18 nmoles/10(7) cells/min, respectively. Considering these results, it is suggested that the two eosinophil subpopulations have distinct biological roles in generating these inflammatory mediators which appear as typical pathological features of allergic rhinitis.

Pathology of equine respiratory disease occurring in association with transport

Eight young thoroughbred horses, taken 1858 km by road (travelling time, 41 h), were examined to assess the pathological nature of respiratory disease associated with transport. Three of the horses showed clinical abnormalities including pyrexia, coughing, leucocytosis and neutrophilia after the first 20 h of transportation. Endoscopical examination of the trachea revealed exacerbation of airway inflammation as a result of transport in two of the three affected horses. A consistent finding in the affected horses was focal serous neutrophilic pneumonia affecting the cranio-ventral portion of the caudal lung lobe with a propensity to affect the right lung. Streptococcus equi subspecies zooepidemicus was isolated from the pneumonic areas, in which corresponding bacterial antigens were identified immunohistochemically. Viral cultures from the pneumonic lesions proved negative for respiratory viruses. It is suggested that transport predisposes the upper respiratory tract and the lower airways to invasion by the bacterium, with episodic pyrexia and acute pneumonia.

Magnetic resonance imaging of femoral marrow in patients with myelodysplastic syndromes or leukemia

We evaluated magnetic resonance imaging (MRI) of femoral marrow in 85 untreated adult patients with myelodysplastic syndromes (MDS) (N = 27), aplastic anemia (N = 9), and leukemia (N = 49). Images of femoral marrow were obtained using a T1-weighted spin-echo (SE) method and a short T1 inversion recovery (STIR) technique. In patients with MDS, the change in MRI pattern from a fatty or nodular pattern to a uniform pattern correlated with disease progression. Evolution to acute leukemia in MDS patients was associated with a higher signal intensity on STIR images (lower signal intensity on T1-weighted SE images) and an extended area of involvement. The femoral marrow in patients with de novo acute myeloid leukemia (AML) showed increased signal and varied patterns (scattered to uniform) on STIR images. However, the faint pattern (grade 4a) was characteristic of M2 AML. In patients with chronic myelogenous leukemia (CML) in the chronic phase, increased leukemic mass was represented by replacement of the femoral marrow with a region of abnormal signal intensity. The extent of involved areas in these CML patients correlated with the spleen size. This study indicates that MRI of femoral marrow is an important tool for the accurate diagnosis and management of patients with MDS and leukemia that may function as an adjunct to bone marrow aspiration and biopsy.

Expression of a cell adhesion molecule, neuropilin, in the developing chick nervous system

Neuropilin (previously known as the A5 protein) is a membrane protein identified in Xenopus and is presumed to be involved in the target recognition of the optic nerve fibers. We have isolated cDNAs encoding the chick homologue of neuropilin, using the Xenopus neuropilin cDNA as a hybridization probe. The predicted amino acid sequence of chick neuropilin is 75% identical to that of the Xenopus homologue. A cell aggregation assay showed that fibroblasts transfected with the chick neuropilin cDNA acquired cell adhesiveness. This adhesion is mediated by a heterophilic interaction between neuropilin and protease-sensitive molecules on fibroblasts. The expression of chick neuropilin is restricted to certain neuronal circuits and is dynamically regulated during development, as is the Xenopus homologue. However, their expression patterns differed significantly in the visual systems between the two species: In the chick optic tectum, the localization of neuropilin is confined to layers d and e of SGFS, two of the six layers receiving the retinal input; the chick optic nerve fibers do not express neuropilin; in the chick retina, amacrine cells transiently express neuropilin. Cultured neurons of the dorsal root ganglia express chick neuropilin on their neurites including growth cones. These results suggests that neuropilin functions as a cell adhesion molecule during the formation of certain neuronal circuits in vivo.

Plexin: a novel neuronal cell surface molecule that mediates cell adhesion via a homophilic binding mechanism in the presence of calcium ions

Plexin (previously referred to as B2) is a neuronal cell surface molecule that has been identified in Xenopus. cDNA cloning reveals that plexin has no homology to known neuronal cell surface molecules but possesses, in its extracellular segment, three internal repeats of cysteine clusters that are homologous to the cysteine-rich domain of the c-met proto-oncogene protein product. The exogenous plexin proteins expressed on the surfaces of L cells by cDNA transfection mediate cell adhesion via a homophilic binding mechanism, under the presence of calcium ions. Plexin is expressed in the receptors and neurons of particular sensory systems. These findings indicate that plexin is a novel calcium-dependent cell adhesion molecule and suggest its involvement in specific neuronal cell interaction and/or contact.