Mesenteric lymph node B lymphoblasts which home to the small intestine are precommitted to IgA synthesis.

The fate of mesenteric lymph node lymphoblasts labeled with either [125I]iododeoxyuridine or [3H]thymidine can be studied after intravenous transfer into syngeneic mice both by measurement of radioactivity in various organs and by combined immunofluorescence and autoradiography of recipient tissues. Many of the lymphoblasts home to the lamina propria of the small intestine within hours of transfer; of these, many visibly secrete IgA. To determine whether the cells that will ultimately secrete IgA are already committed to IgA synthesis before their arrival in the gut, mesenteric lymph node cell populations were treated with various class-specific antisera to mouse immunoglobulins before transfer. Treatment with antiserum to IgA, plus complement, reduced the fraction of injected label recovered from the recipients' intestines, and also reduced the proportion of donor (labeled) cells containing IgA. We conclude that mesenteric lymph nodes are probably the principal source of IgA-secreting plasma cells in the lamina propria of the gut, and that the cells become committed to IgA synthesis and develop cell surface IgA before emigrating. This IgA is apparently synthesized by the cells that bear it since it is not removed by extensive rinsing at 37 degrees C, a maneuver that elutes passively adsorbed immunoglobulin.

Origin of IgA-secreting plasma cells in the mammary gland.

Lymphoblasts from the mesenteric lymph nodes (MN) of mice home to the mammary glands of syngeneic recipients late in pregnancy and during lactation, and within hours of transfer most can be shown to contain IgA. Homing does not occur in virgins, in early pregnancy, or after weaning. Homing MN lymphoblasts are sensitive to antiserum to IgA plus complement, but not to other class-specific antisera. Thus, lymphoblasts in MN with the potential to home to the mammary gland are already committed to IgA synthesis and bear surface IgA before reaching their destination. These results explain observations, made by others, of specific IgA antibodies and IgA plasma cells in milk and colostrum after oral immunization. Under natural conditions it is likely that IgA precursor cells, after stimulation in the gut-associated lymphoid tissue by intestinal antigens, migrate to the mammary gland where they secrete antibodies which constitute an important defense mechanism of the newborn. In the absence of lactation, these cells probably form part of the normal traffic to the lamina propria of the small intestine.

Cell surface immunoglobulin. XI. The appearance of an IgD-like molecule on murine lymphoid cells during ontogeny.

An Ig molecule containing L chains and H chains similar to human delta-chains has been detected on the surface of radioiodinated murine lymphoid cells. Newborn mice have only IgM on their splenocytes. Between 10 and 15 days, the IgD-like molecule appears and increases in amount until 3 mo of age, when it is the predominant cell surface Ig in terms of radioactivity. IgD is found only in peripheral lymphoid tissues and is present in larger amounts on peripheral lymph node cells (approximately 85% of surface Ig) than on splenocytes (approximately 50%). IgD is also present in comparable amounts on cells from both nu/nu and germfree mice, indicating that its expression may be independent of both thymic influence and antigenic stimulation. These studies suggest that there is a switch from cell surface IgM to IgD that occurs during differentiation of virgin B lymphocytes in the spleen.

Mutations in the human immunodeficiency virus type 1 polypurine tract (PPT) reduce the rate of PPT cleavage and plus-strand DNA synthesis.

Previously, we analyzed the effects of point mutations in the human immunodeficiency virus type 1 (HIV-1) polypurine tract (PPT) and found that some mutations affected both titer and cleavage specificity. We used HIV-1 vectors containing two PPTs and the D116N integrase active-site mutation in a cell-based assay to measure differences in the relative rates of PPT processing and utilization. The relative rates were measured by determining which of the two PPTs in the vector is used to synthesize viral DNA. The results indicate that mutations that have subtle effects on titer and cleavage specificity can have dramatic effects on rates of PPT generation and utilization.

Oroclinal bending of the southern sierra nevada batholith.

Structural, magmatic, and isotopic features of the southern Sierra Nevada batholith are deflected clockwise with respect to its central and northern parts. Directions of magnetization at three localities in the southern Sierra Nevada are progressively deflected; this is consistent with the hypothesis that the region was tectonically rotated in an orocline. No paleomagnetic deflection was observed northwest of the White Wolf-Kern Canyon fault system. Oroclinal bending ofa block bounded by the San Andreas, Garlock, and White Wolf-Kern Canyon faults may have occurred before about 16 x l0(6) years ago. The deformation may have been a response to shear at the western boundary of the North American plate caused by oblique subduction.

40Ar/39Ar Dating of the Brunhes-Matuyama Geomagnetic Field Reversal.

Magnetostratigraphic studies are widely used in conjunction with the geomagnetic polarity time scale (GPTS) to date events in the range 0 to 5 million years ago. A critical tie point on the GPTS is the potassium-argon age of the most recent (Brunhes-Matuyama) geomagnetic field reversal. Astronomical values for the forcing frequencies observed in the oxygen isotope record in Ocean Drilling Project site 677 suggest that the age of this last reversal is 780 ka (thousand years ago), whereas the potassium-argon-based estimate is 730 ka. Results from 4039; Ar incremental heating studies on a series of lavas from Maui that straddle the Brunhes-Matuyama reversal give an age of 783 + 11 ka, in agreement with the astronomically derived value. The astronomically based technique appears to be a viable tool for dating young sedimentary sequences.

Southern hemisphere origin of the cretaceous laytonville limestone of california.

New paleomagnetic, paleontologic, and stratigraphic data from outcrops of the Laytonville Limestone (101 to 88 million years old) support a Southern Hemisphere origin. A paleomagnetic megaconglomerate test is statistically significant and suggests magnetization at 14 degrees +/- 5 degrees south, predating Late Cretaceous to Eocene (70 to 50 million years ago) accretion. Rapid Kula plate movement or the existence and demise of a now vanished oceanic plate (or both) are required to accommodate the greater than 50 degrees of poleward displacement implied by the paleomagnetic data. This rapid motion brings into question the validity of a "speed limit" for absolute plate velocity based on present-day plate motions.

Coeval 40Ar/39Ar Ages of 65.0 Million Years Ago from Chicxulub Crater Melt Rock and Cretaceous-Tertiary Boundary Tektites.

(40)Ar/(39)Ar dating of drill core samples of a glassy melt rock recovered from beneath a massive impact breccia contained within the 180-kilometer subsurface Chicxulub crater in Yucatán, Mexico, has yielded well-behaved incremental heating spectra with a mean plateau age of 64.98 +/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from (40)Ar/(39)Ar ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 +/- 0.08 Ma (mean plateau age for Beloc) and 65.07 +/- 0.10 Ma (mean total fusion age for both sites). The (40)Ar/(39)Ar ages, in conjunction with geochemical and petrological similarities, strengthen the recent suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.

Immunoglobulin-bearing and complement-receptor lymphocytes constitute the same population in human peripheral blood.

Complement-receptor lymphocytes have generally been considered to be a subpopulation of bone-marrow derived (B) lymphocytes. However, the present studies show that essentially all cells with integral surface immunoglobulin from normal human peripheral blood bear receptors for the third component of complement. Moreover, after removal of phagocytes, all cells with complement receptors bear surface Ig. Thus, circulating B cells and complement-receptor lymphocytes are the same population.

The ras oncogene-mediated sensitization of human cells to topoisomerase II inhibitor-induced apoptosis.

BACKGROUND: Among the inhibitors of the enzyme topoisomerase II (an important target for chemotherapeutic drugs) tested in the National Cancer Institute's In Vitro Antineoplastic Drug Screen, NSC 284682 (3'-hydroxydaunorubicin) and NSC 659687 [9-hydroxy-5,6-dimethyl-1-(N-[2(dimethylamino)ethyl]carbamoyl)-6H-pyrido -(4,3-b)carbazole] were the only compounds that were more cytotoxic to tumor cells harboring an activated ras oncogene than to tumor cells bearing wild-type ras alleles. Expression of the multidrug resistance proteins P-glycoprotein and MRP (multidrug resistance-associated protein) facilitates tumor cell resistance to topoisomerase II inhibitors. We investigated whether tumor cells with activated ras oncogenes showed enhanced sensitivity to other topoisomerase II inhibitors in the absence of the multidrug-resistant phenotype. METHODS: We studied 20 topoisomerase II inhibitors and individual cell lines with or without activated ras oncogenes and with varying degrees of multidrug resistance. RESULTS: In the absence of multidrug resistance, human tumor cell lines with activated ras oncogenes were uniformly more sensitive to most topoisomerase II inhibitors than were cell lines containing wild-type ras alleles. The compounds NSC 284682 and NSC 659687 were especially effective irrespective of the multidrug resistant phenotype. The ras oncogene-mediated sensitization to topoisomerase II inhibitors was far more prominent with the non-DNA-intercalating epipodophyllotoxins than with the DNA-intercalating inhibitors. This difference in sensitization appears to be related to a difference in apoptotic sensitivity, since the level of DNA damage generated by etoposide (an epipodophyllotoxin derivative) in immortalized human kidney epithelial cells expressing an activated ras oncogene was similar to that in the parental cells, but apoptosis was enhanced only in the former cells. CONCLUSIONS: Activated ras oncogenes appear to enhance the sensitivity of human tumor cells to topoisomerase II inhibitors by potentiating an apoptotic response. Epipodophyllotoxin-derived topoisomerase II inhibitors should be more effective than the DNA-intercalating inhibitors against tumor cells with activated ras oncogenes.

Ras oncogene-induced sensitization to 1-beta-D-arabinofuranosylcytosine.

Human tumor cells containing ras oncogenes display enhanced sensitivity to 1-beta-D-arabinofuranosylcytosine (Ara-C) and other deoxycytidine analogues (H-M. Koo, et al., Cancer Res., 56: 5211-5216, 1996). Human tumor cell lines with or without a ras oncogene as well as a pair of isogenic cell lines with one containing an activated ras oncogene were used to study the basis for differential sensitivity. We found that human tumor cells containing ras oncogenes upon entry into the S phase of the cell cycle underwent apoptosis in response to Ara-C treatment. By contrast, human tumor cells harboring wild-type ras alleles were only delayed in the S phase when exposed to Ara-C. Thus, the ras oncogene specifically renders human cells more sensitive to Ara-C by preventing S-phase arrest. This may occur by the ras oncogene compromising an S-phase checkpoint.

Enhanced sensitivity to 1-beta-D-arabinofuranosylcytosine and topoisomerase II inhibitors in tumor cell lines harboring activated ras oncogenes.

We used human tumor cell lines from the National Cancer Institute's In Vitro Antineoplastic Drug Screen to assess whether sensitivity to any of the approximately 45,000 compounds tested previously correlated with the presence of a ras oncogene. Among these cell lines, the mutations in Ki-ras2 clustered in non-small cell lung and colon carcinoma subpanels, and five of the six leukemia lines contained mutations in either N-ras or Ki-ras2. These analyses revealed a striking correlation with 1-beta-D-arabinofuranosylcytosine (Ara-C) and 2,2'-O-cyclocytidine sensitivity in the cell lines harboring ras mutations compared to the tumor lines with wild-type ras alleles. Strong correlations were also found with topoisomerase (topo) II inhibitors, especially 3'-hydroxydaunorubicin and an olivacine derivative. These differential sensitivities persisted in an additional 22 non-small cell lung carcinoma lines (ras mutations, n = 12 and wild-type ras, n = 10). Thus, the association with Ara-C sensitivity was greatest while topo II inhibitors showed a lower, but significant, correlation. These results suggest that the ras oncogene may play a determinant role in rendering tumor cells sensitive to deoxycytidine analogues and topo II inhibitors.

Characterization of the ototoxicity of difluoromethylornithine and its enantiomers.

Difluoromethylornithine (DFMO) is an irreversible inhibitor of ornithine decarboxylase (ODC), the essential enzyme in mammalian polyamine biosynthesis (Pasic et al., 1997, Arch. Otolaryngol. Head Neck Surg. 123[12], 1281-1286). This cancer chemotherapeutic agent has significant ototoxic potential. Because the DFMO enantiomers differ in their ability to block ODC, the present study was designed to compare the ototoxic potential of each enantiomer with the racemic form of this drug for the rat and guinea pig. Determining differential ototoxicity of the enantiomers is one preliminary step in determining the optimal form of DFMO to use in human cancer chemotherapy. Daily intubation with D,L-DFMO does not produce any auditory dysfunction in rats with doses between 200 mg/kg/day and 1. 2 g/kg/day for up to 8 weeks, despite the fact that doses of 800 and 1200 mg/kg/day depressed body weight gain. In contrast to the data observed in rats, substantial ototoxicity was observed when guinea pigs were injected ip with doses of D,L-DFMO between 500 mg/kg/day and 1 g/kg/day. D,L-DFMO produced loss of compound action potential sensitivity, but not of cochlear microphonic amplitude. This finding correlated with histological data revealing loss of both outer and inner hair cells in the cochlea with inner more affected than outer hair cells, particularly in the basal turn. Higher exposure doses (2-3 g/kg/day) resulted in significant general toxicity including impaired growth and some mortality. When the enantiomers were evaluated in the guinea pig, it was found that 1 g/kg/day D-DFMO did not produce any significant hearing impairment, whereas 1 g/kg/day of the L-enantiomer of DFMO generated a threshold shift that surpassed that of 1 g/kg/day of the D,L-DFMO treatment.

Caffeine content of common beverages.

Tea, coffee, carbonated and chocolate beverages were analyzed for caffeine, and results compared in terms of usual serving sizes. Significant differences in caffeine levels were found to result from the preparation method of coffee or brewing time of tea. It is possible for a cup of tea, instant coffee, or can of cola beverage to have similar caffeine content (55 to 65 mg.); however, the mean values per cup of black tea (28 to 46 mg.) are considerably lower than for brewed coffee (107 to 151 mg.). Caffeine is readily absorbed and can have pharmacologic effects on adults or on children who consume quantities of cola beverages or chocolate. Both preparation method and quantity of beverage consumed should be considered in taking dietary histories or estimating caffeine intake.

Succinate dehydrogenase (SDH) activity in hair cells: a correlate for permanent threshold elevations.

Hair cell loss is often used as a histological correlate of hearing loss. However, the histological and the physiological data are not always well correlated. This paper investigates the use of succinate dehydrogenase (SDH) activity in the hair cells as a marker of cellular dysfunction and so the loss of auditory sensitivity. In our previous studies, potentiation of noise-induced auditory threshold elevation by carbon monoxide (CO) was observed [Chen and Fechter, 1999; Chen et al., 1999]. However, its histological basis is still unclear. In this study, rats were exposed to 100-dB octave-band noise (center frequency=13.6 kHz, 2 h) or to the combination of the noise and CO (1200 ppm). Threshold elevation of compound action potential (CAP) and cochlear histological changes were assessed 4 weeks after exposure. The noise alone caused CAP threshold elevations with little if any or without hair cell loss. However, the SDH activity in the hair cells decreased after the exposure. The SDH reduction, especially in the inner hair cells, was well related to the loss of auditory sensitivity. The combined exposure to noise and CO caused more severe CAP threshold elevation and SDH activity reduction than did the noise alone and it also caused significant outer hair cell loss. However, across all the test frequencies, neither the hair cell loss nor the SDH reduction alone had good correlation to the reduction of the auditory sensitivity. Under this situation, CAP threshold elevation seemed to follow OHC loss at high frequencies and to follow SDH reductions in the IHCs at low frequencies, where no hair cell loss occurred.

Intermittent noise-induced hearing loss and the influence of carbon monoxide.

Intermittent noise causes less hearing loss than continuous noise of equal intensity. The reduction in damage observed with intermittent noise may be explained by the fact that the auditory system has time to recover between the noise phases. Simultaneous carbon monoxide (CO) exposure produces greater noise-induced hearing loss than does noise alone (Chen and Fechter, 1999). In the present study, intermittent noise (octave-band with a center frequency of 13.6 kHz, 100 dB) of a 2 h total duration but with a different duty cycle (% of noise during exposure) was used. The intermittent exposure that had a shorter noise duty cycle induced a less permanent threshold shift (PTS) than those that had a longer noise duty cycle (or less rest periods). This relation between the loss in compound action potential (CAP) sensitivity and the noise duty cycle (or rest period) was abolished by the presence of CO. The cochlear microphonic (CM) amplitude revealed similar results to those seen using the CAP. While intermittent noise that had a short noise duty cycle did not cause hair cell loss by itself, the combined exposure to noise and CO (1200 ppm) caused remarkable OHC loss in the basal turn.

The folic acid analogue methotrexate protects frog embryo cell membranes against damage by the potato glycoalkaloid alpha-chaconine.

As part of an effort to improve the safety of plant foods, a need exists to more clearly delineate the mechanisms of toxicities of glycoalkaloids, which may be present in Solanum plant species such as potatoes, tomatoes and eggplants. Alpha-chaconine is a major glycoalkaloid present in potatoes. To assess the possible influence of structure of pteridine derivatives on toxicity of potato glycoalkaloids, a previous study that demonstrated the protective effects of folic acid against the Solanum glycoalkaloid alpha-chaconine-induced toxicity on Xenopus laevis frog embryo cell membranes was extended to two folate analogues--a synthetic compound widely used as a therapeutic agent methotrexate, and naturally occurring L-monapterin. Adverse effects on embryos were evaluated by observing changes in membrane potentials with an electrochromic dye, di-4-ANEPPS, as a fluorescent probe for the integrity of the membranes. Methotrexate decreased alpha-chaconine-induced polarization, as did folic acid. This decrease may result from an alteration of membrane conformations that prevents the binding of the glycoalkaloid to the membrane receptor sites, and/or from effects on folic acid metabolism. In contrast, L-monapterin did not significantly reduce the alpha-chaconine-induced toxicity. The possible significance of these results to food safety is discussed.

Developmental toxicology of solamargine and solasonine glycoalkaloids in frog embryos.

As part of an effort to improve the safety of plant foods, a need exists to define the relative toxicities of structurally different glycoalkaloids and metabolites which may be present in Solanum plant species such as potatoes, tomatoes and eggplants. The objectives of this study were to determine the relative toxicities and the modes of action of the eggplant (Solanum melongena) glycoalkaloids solamargine and solasonine in Xenopus laevis frog embryos, using membrane potential and embryo growth and teratogenicity assays. In the cell membrane assays, adverse effects on embryos were evaluated by measuring membrane potentials using an electrochromic dye, di-4-ANEPPS, as a fluorescence probe for the integrity of the membranes. In the embryo growth and teratogenesis assays, the survival of the embryos and organ malformations was used as an index of embryo toxicity. The relative potencies of glycoalkaloids are similar for frog embryo effects (survival and teratogenicities) and for membrane effects (membrane potential). Experiments with solasonine at pH 6 and 8 suggest that the unprotonated form of the glycoalkaloids appears to be involved in the membrane effects. The nature of the carbohydrate side-chains of the steroidal glycosides governs relative potencies. The possible significance of the findings to food safety and plant physiology and possible application of the membrane assays to bacterial toxins are discussed.