Evidence for a human IgG1 class switch program

In activated murine B lymphocytes, immunoglobulin class switch recombination occurs as a highly regulated process which is targeted to distinct switch regions. Here we present first evidence that in human B lymphocytes, switch recombination is targeted to distinct switch regions as well. In a panel of clonally unrelated IgG1-expressing human B cells, immortalized by Epstein-Barr virus (EBV) transformation, seven out of nine cells show switch recombination between Sμ and Sγ1 on both alleles, the active and inactive one. The remaining cells show no switch recombination on the inactive IgH locus. The very strong correlation of switch recombination on both alleles of IgG1-expressing cells proves that class switch recombination to IgG1 is not random but directed in human B lymphocytes.     

Stimulation of insulin release is uncoupled from insulin biosynthesis in tumoral RINm5F cells.

RINm5F cells, an insulin-secreting subclone of a rat insulinoma cell line, were incubated in serum-free medium up to 24 hours in the presence or absence of glucagonlike peptide-1(7-36)amide in various concentrations, 3-isobutyl-1 methylxanthine (1 mM), choleratoxin (10 nM), carbachol (1 mM), and potassium (40 mM). Insulin release and biosynthesis were measured by the immunoreactive insulin content of the cells and the medium. Steady-state levels of insulin-specific mRNA were determined by Northern and slot blot analysis. Short-term insulin release is significantly stimulated by all secretagogues tested. A significant increase of insulin biosynthesis by any of the various secretagogues was not detectable on the peptide and mRNA level. Sodium butyrate (1 mM), a differentiating agent, increased insulin-specific mRNA levels in RINm5F cells after 72 hours. In conclusion, substances known to stimulate short-term insulin release in RINm5F cells do not stimulate insulin biosynthesis, indicating an uncoupling of insulin secretion and biosynthesis in these transformed beta cells.     

Time course of some effects of cigarette smoking on platelets.

Eight male habitual smokers smoked two cigarettes over a 20-min period following a 12-h period of abstinence. Antecubital venipuncture was performed immediately before, immediately after, and 55 min and 2 h after smoking had ceased. At these times, the mean values (+/- SD) of collagen-induced platelet aggregation were 45 +/- 5, 68 +/- 5, 59 +/- 6 and 52 +/- 5 chart units, respectively, while the corresponding values for the mean platelet aggregate ratio were 0.91 +/- 0.01, 0.82 +/- 0.03, 0.87 +/- 0.02 and 0.90 +/- 0.02, respectively. Mean collagen-induced platelet aggregation was significantly (P less than 0.005) higher immediately after, and 55 min and 2 h after smoking. The mean platelet aggregate ratio was significantly (P less than 0.001) lower immediately after and 55 min after smoking. Correlation coefficients between the concentration of nicotine in each of the 24 plasma samples obtained after smoking and the corresponding values of collagen-induced platelet aggregation and the platelet aggregate ratio were 0.41 (P less than 0.05) and -0.50 (P less than 0.02), respectively. It is concluded that when habitual smokers abstain from smoking overnight, a 20-min period of cigarette smoking may enhance platelet aggregability for as long as 2 h.     

The road to the discovery of the p53 protein: The Steiner Cancer Prize Award Lecture

Linxian, China has some of the highest rates of esophageal/gastric cardia cancer in the world. In 1983, esophageal balloon cytology screening was performed in 3 communes in northern Linxian. Of the participants, 10,066 with no evidence of cancer were followed prospectively for 71/2 years to evaluate the ability of the initial cytologc diagnoses to identify individuals at increased risk for developing cancer of the esophagus or gastric cardia. A total of 747 incident cases of esophageal or cardia cancer and 322 deaths due to these tumors were identified during the follow-up period and used in this analysis. The risks for esophageal or cardia cancer incidence and mortality increased in parallel with the presumed severity of the 1983 Chinese cytologic diagnoses. After adjusting for potential confounding factors, relative risks for esophageal or cardia cancer incidence, by initial cytologic diagnosis, were normal = 1.00 (reference), hyperplasia = 1.25, dysplasia 1 = 2.20, dysplasia 2 = 4.22 and near-cancer = 5.96. Our results suggest that esophageal balloon cytology, as performed and interpreted in Linxian in 1983, successfully identified individuals at increased risk for developing cancer of the esophagus or gastric cardia. © 1994 Wiley-Liss, Inc.     

Sexual origins of British Aspergillus nidulans isolates.

Aspergillus nidulans is a holomorphic fungus, capable of producing both meiotically and mitotically derived spores. Meiosis may be an evolutionary relic in this species because it is potentially capable of mitotic recombination and because most Aspergilli lack the ability to produce meiotic spores. We tested the null hypothesis that meiosis has been a major factor in the origin of strains of A. nidulans from Great Britain by estimating linkage disequilibrium among restriction fragment length polymorphisms. These strains belong to different heterokaryon compatibility groups and are thus incapable of undergoing mitotic recombination with one another, so any recombination evidenced by linkage equilibrium is assumed to be the result of meiosis. Eleven cosmid clones of known chromosomal origin were used to generate multilocus genotypes based on restriction-pattern differences for each heterokaryon compatibility group. Low levels of genetic variation and little linkage disequilibrium were found, indicating that the heterokaryon compatibility groups represent recently diverged lineages that arose via meiotic recombination. The null hypothesis that loci are independent could not be rejected. Additionally, low levels of electrophoretic karyotype variation were indicative of meiosis. We conclude that although A. nidulans probably propagates in a primarily clonal fashion, recombination events are frequent enough to disrupt the stable maintenance of clonal genotypes. We further conclude that the British heterokaryon compatibility groups arose via recombination and not through novel mutation.     

Total anomalous pulmonary venous drainage. Seventeen-year surgical experience

Between 1968 and 1985, 80 children underwent correction of total anomalous pulmonary venous drainage. There were 47 boys and 33 girls whose ages ranged from 3 days to 16 years (median 2 months, interquartile range 5 years). Seventy (87.5%) were less than 1 year of age at operation. Fifty-eight (72.5%) weighed less than 5 kg, the range being 1.6 to 42 kg (median 3.7 kg, interquartile range 2.4 kg). Forty-five (56%) patients had supracardiac, 14 (17.5%) cardiac, 15 (19%) infracardiac, and 6 (7.5%) had mixed total anomalous pulmonary venous drainage. Follow-up was complete in 78 (97.5%) and ranged from 6 to 189 months (median 58 months, interquartile range 59 months). There were 14 (17.5%) early and six (7.5%) late deaths. Analysis by various factors revealed year of operation as the only factor to affect survival at the 5% level of significance. Early mortality was 29% between 1968-1977 and 11% between 1978-1985 (p = 0.04). Postoperative pulmonary venous obstruction occurred in five (6%) patients between 6 weeks and 3 months after operation. All 5 died, three after reoperation. Five (6%) other children had reoperations, four for residual shunts and one for superior vena caval obstruction.     

Disposition of oral and intravenous pravastatin in MRP2-deficient TR- rats.

The aim of this study was to characterize the role of the efflux transporter Mrp2 (Abcc2) in the pharmacokinetics of orally and intravenously administered pravastatin in rats. Eight Mrp2-deficient TR- rats and eight wild-type rats were given an oral dose of 20 mg/kg pravastatin. Four TR- animals and four wild-type animals were studied after intravenous administration of pravastatin (5 mg/kg). The TR(-) rats showed a 6.1-fold higher mean area under the plasma concentration-time curve (AUC) of pravastatin (p < 0.001) after oral administration and a 4.7-fold higher AUC (p < 0.01) after intravenous administration of pravastatin as compared with the wild-type animals. The mean systemic (total) clearance of pravastatin was 4.6-fold higher (39.2 versus 8.50 l/h/kg, p < 0.001) and the mean V 4.3-fold higher (14.1 versus 3.29 l/kg, p < 0.01) in the wild-type rats. The mean renal clearance of pravastatin in the TR(-) rats was 16.5-fold increased as compared with the wild-type animals (0.695 versus 0.042 l/h/kg, p < 0.05). The increased systemic exposure to oral pravastatin in the TR- rats was associated with a greater inhibitory effect on 3-hydroxy-3-methylglutaryl CoA reductase, as shown by smaller lathosterol to cholesterol concentration ratios. These results suggest that the reduced biliary pravastatin excretion in the Mrp2-deficient TR- rats is partly compensated for by increased urinary excretion of pravastatin. Furthermore, intestinal Mrp2 does not appear to play a major role in the oral absorption of pravastatin in normal rats.