Murine interleukin 7 (IL-7) receptor. Characterization on an IL-7-dependent cell line.

A murine cell line (IxN/2b) absolutely dependent upon exogenous IL-7 for continued growth has been obtained that expresses lymphoid precursor and class I MHC antigens and also contains a rearranged mu heavy chain. This cell line has been used to define the binding and structural characteristics of the murine IL-7 receptor using 125I-labeled recombinant murine IL-7. 125I-IL-7 binding to IxN/2b cell was rapid and saturable at both 4 degrees and 37 degrees C. Equilibrium binding studies produced curvilinear Scatchard plots at both temperatures with high and low affinity Ka values of approximately 1 x 10(10) M-1 and 4 x 10(8) M-1, respectively, and a total of 2,000-2,500 IL-7 binding sites expressed per cell. Experiments measuring inhibition of binding of 125I-IL-7 by unlabeled IL-7 also produced data consistent with the existence of two classes of IL-7 receptors. Evidence concerning the possible molecular nature of two classes of IL-7 receptors was provided by dissociation kinetics and affinity crosslinking experiments. The dissociation rate of 125I-IL-7 was markedly increased when measured in the presence of unlabeled IL-7 at both 37 degrees and 4 degrees C, which is diagnostic of a receptor population displaying negative cooperativity. Crosslinking studies showed that under both reducing and nonreducing conditions, the major crosslinked species observed corresponded to a receptor size of 75-79 kD while a less intense higher molecular mass crosslinked species was also seen which corresponded to a receptor size approximately twice as large (159-162 kD). Both types of experiments suggest that the IL-7 receptor may form noncovalently associated dimers in the membrane. The IL-7 receptor was expressed on pre-B cells, but not detected on several murine B cell lines or primary mature B cells. It was also expressed on murine thymocytes, some T lineage cell lines, and on bone marrow-derived macrophage. All cells binding 125I-IL-7 exhibited curvilinear Scatchard plots. No cytokines or growth factors tested were able to inhibit binding of 125I-IL-7 to its receptor. These results define the initial binding and structural characteristics, and the cellular distribution, of the murine IL-7 receptor.

Brassica campestris L.: Floral Induction by One Long Day.

A strain of Brassica campestris L. responds to a single photoinductive cycle 4 days after sowing. Extending the photoperiod from 8 to 22 or 24 hours, with incandescent light of 538-lux intensity, induced inflorescence in 90 percent of the plants. Inflorescence development was visible on dissection 5 or 6 days after photoinduction. Floral induction increased with duration and intensity of the supplementary light.

The IL-6 signal transducer, gp130: an oncostatin M receptor and affinity converter for the LIF receptor.

Leukemia inhibitory factor (LIF) and interleukin-6 (IL-6) are multifunctional cytokines with many similar activities. LIF is structurally and functionally related to another cytokine, Oncostatin M (OSM), that binds to the high-affinity LIF receptor but not to the low-affinity LIF receptor. A complementary DNA was isolated that encodes the high-affinity converting subunit of the LIF receptor. The converter conferred high-affinity binding of both LIF and OSM when expressed with the low-affinity LIF receptor and is identical to the signal transducing subunit of the IL-6 receptor, gp130. The gp130 subunit alone confers low-affinity binding of OSM when expressed in COS-7 cells. This receptor system resembles the high-affinity receptors for granulocyte-macrophage colony-stimulating factor, IL-3, and IL-5, which share a common subunit.

Cutaneous perianal recurrence of cancer after anterior resection using the EEA stapling device.

We present a case of cutaneous recurrence from an adenocarcinoma of the rectum, which was diagnosed 7 months after anterior resection of the primary tumour had been performed using the EEA stapling device to fashion the anastomosis. We propose that the recurrence was caused by the seeding of exfoliated tumour cells into an area of perianal skin which was abraded during the introduction of the stapling gun.

Shade adaptation of photosynthesis in Coffea arabica.

The effect of irradiance on the rate of net photosynthesis was measured for mature leaves of coffee grown under five levels of radiation from 100% to 5% daylight. The rate of light-saturated photosynthesis per unit leaf area (PNmax) increased from 2 µmol CO2 m(-2) s(-1) under 5% daylight to 4.4 µmol CO2 m(-2) s(-1) under 100% daylight. The photon flux density (PAR, photosynthetically active radiation) needed for 50% saturation of photosynthesis, as well as the light compensation point, also increased with increasing levels of irradiation during growth. The quantum efficiency of photosynthesis (α), measured by the initial slope of the photosynthetic response to increasing irradiance, was greater under shaded growth conditions. The rate of dark respiration was greatest for plants grown in full daylight. On the basis of the increase in the quantal efficiency of photosynthesis and the low light compensation point when grown under shaded conditions, coffee shows high shade adaptation. Plants adjusted to shade by an increased ability to utilize short-term increases in irradiance above the level of the growth irradiance (measured by the difference between photosynthesis at the growth irradiance, PNg, and PNmax).

Participation of Photosynthesis in Floral Induction of the Long Day Plant Anagallis arvensis L.

The saturating photon flux density (400 to 700 nanometers) for induction of flowering of the long day plant Anagallis arvensis L. was 1,900 micromoles per square meter per second (6,000 foot-candles) when an 8-hour daylength was extended to 24 hours by a single period of supplementary irradiation. The saturating photon flux density for photosynthetic CO(2) uptake during the same single supplementary light period was lower, at about 1,000 to 650 micromoles per square meter per second (3,000 to 2,000 foot-candles).The per cent flowering and mean number of floral buds per plant were significantly reduced when the light extension treatment was given in CO(2)-free air, and glucose (10 kilograms per cubic meter in water) relieved this effect. Glucose solution also significantly increased flowering of plants given supplementary light treatment in atmospheric air under a photon flux density of 80 micromoles per square meter per second. Increasing the CO(2) concentration to 1.27 grams per cubic meter of CO(2) in air during the supplementary light period did not increase flowering.It is concluded that high photon flux densities promote flowering of Anagallis through both increased photosynthesis and the photomorphogenic action of high irradiance.

Promotion of Flowering in Brassica campestris L. cv Ceres by Sucrose.

Flower initiation of the quantitative long-day plant Brassica campestris cv Ceres was earlier and at a lower final leaf number when sucrose was added to the medium in which plants were grown in sterile culture. The optimal concentration of sucrose was 40 to 80 millimolar. This flower-promoting effect of sucrose was not osmotic, as mannitol, sodium chloride, and polyethylene glycol were not effective at equal osmotic potentials.Seedlings grown heterotrophically after treatment with 4-chloro-5-(dimethylamino)-2-phenyl-3-(2H)-pyridazinone to prevent chlorophyll accumulation were also induced to form flower primordia earlier as the sucrose concentration in the medium was increased up to 80 millimolar. Inclusion of 4 millimolar sodium nitrate in the culture medium of green plants did not reduce the flower-promoting effects of sucrose but delayed initiation in plants grown without added sucrose.Removal of CO(2) during a single main or supplementary light period, or both, greatly reduced flower initiation. It is concluded that sucrose may be an important controlling factor determining floral initiation in Brassica.

Photosynthetic and leaf morphological characteristics in Leucaena leucocephala as affected by growth under different neutral shade levels.

Morphological and physiological measurements on individual leaves of Leucaena leucocephala seedlings were used to study acclimation to neutral shading. The light-saturated photosynthetic rate (Pn max) ranged from 19.6 to 6.5 µmol CO2 m(-2) s(-1) as photosynthetic photon flux density (PPFD) during growth decreased from 27 to 1.6 mol m(-2) s(-1). Stomatal density varied from 144 mm(-2) in plants grown in high PPFD to 84 mm(-2) in plants grown in low PPFD. Average maximal stomatal conductance for H2O was 1.1 in plants grown in high PPFD and 0.3 for plants grown in low PPFD. Plants grown in low PPFD had a greater total chlorophyll content than plants grown in high PPFD (7.2 vs 2.9 mg g(-1) on a unit fresh weight basis, and 4.3 vs 3.7 mg dm(-2) on a unit leaf area basis). Leaf area was largest when plants were grown under the intermediate PPFDs. Leaf density thickness was largest when plants were grown under the largest PPFDs. It is concluded that L. leucocephala shows extensive ability to acclimate to neutral shade, and could be considered a facultative shade plant.

Oncostatin M and leukemia inhibitory factor trigger overlapping and different signals through partially shared receptor complexes.

Leukemia inhibitory factor (LIF) and oncostatin M (OSM) both bind to the same receptor with high affinity and thus mediate an overlapping spectrum of biological activities, the signal transduction mechanisms for which are unclear. We show that mitogen-activated protein kinases are involved in both the LIF and OSM signal transduction pathways. However, we found that OSM is a much more potent inducer of both mitogen-activated protein kinase activity and biological response, both of which correlate with the expression of a second OSM receptor that does not bind LIF. In addition, different patterns of tyrosine-phosphorylated proteins were stimulated by OSM and LIF. We therefore suggest that the two receptors for OSM can be coupled to different signal transduction events.

Symptomatic pancreatic heterotopia treated by local excision.

Non-ulcer dyspepsia is a continuing problem and in many cases a precise cause is never identified. We present five patients with an allegedly uncommon condition--pancreatic heterotopia. They were managed by local excision of the tumour and after a mean (range) follow up of 42 (9-80) months all remain free of the original symptoms.

Identification of a novel low-affinity receptor for human interleukin-7.

Human recombinant interleukin-7 (IL-7) was labeled with biotin and used to examine IL-7 receptor (IL-7R) expression and regulation on human primary hematopoietic cells, the monocytoid line THP1, and a range of B- and pre-B-celi lines by flow cytometry. A strong intensity of staining was observed using relatively high (greater than 1 x 10(-7) mol/L) concentrations of biotinylated IL-7 on the majority of cell types examined. This reactivity, which could be effectively competed with excess unlabeled IL-7, did not correlate with either mRNA levels for the cloned receptor or with estimates of IL-7R expression determined by [125I]IL-7 binding. Staining of cells with a titration of biotinylated IL-7 showed, at concentrations greater than 1 x 10(-7) mol/L binding with a Ka in the range of 1 x 10(6) mol/L-1, to 1 x 10(7) mol/L-1, an affinity 100 to 1,000 times lower than that reported for the cloned IL-7 receptor. Further data suggesting the existence of a distinct low- affinity IL-7R were provided by two antibodies specific for the cloned IL-7R. Staining with these monoclonal antibodies (MoAbs) correlated with both IL-7R mRNA levels and receptor expression determined by [125I]IL-7 binding, but was not compatible with the distribution of reactivity seen with biotinylated IL-7. Using tritiated biotin to label IL-7, it was estimated that the total number of IL-7 binding sites on the cell lines examined ranged from 1 x 10(4) to at least 5 x 10(5)/cell. Cross-linking studies showed that [125I]IL-7 associated with two major proteins of approximately 62 Kd and 70 Kd on the surface of RPMI 1788 and THP1 cells, in contrast to the 75- to 80 Kd molecule characteristic of the previously cloned receptor, expressed on the surface of Daudi cells. Proliferation of THP1 cells, expressing only the low-affinity form of IL-7R and lacking detectable IL-7R mRNA, could be inhibited by the addition of IL-7 in a concentration-dependent fashion, indicating that, at least on this cell line, binding of IL-7 with a Ka of 1 x 10(6) mol/L-1 to 1 x 10(7) mol/L-1 can transduce a biological signal. Taken together, the data contained in this report demonstrate the existence of a low-affinity IL-7R, expressed in high numbers on hematopoietic cells of different lineages, which is the product of a gene distinct from that encoding the cloned IL-7R.

Identification and cloning of a novel IL-15 binding protein that is structurally related to the alpha chain of the IL-2 receptor.

Interleukin-15 (IL-15) is a novel cytokine of the four-helix bundle family which shares many biological activities with IL-2, probably due to its interaction with the IL-2 receptor beta and gamma (IL-2R beta and gamma c) chains. We report here the characterization and molecular cloning of a distinct murine IL-15R alpha chain. IL-15R alpha alone displays an affinity of binding for IL-15 equivalent to that of the heterotrimeric IL-2R for IL-2. A biologically functional heteromeric IL-15 receptor complex capable of mediating IL-15 responses was generated through reconstruction experiments in a murine myeloid cell line. IL-15R alpha is structurally similar to IL-2R alpha; together they define a new cytokine receptor family. The distribution of IL-15 and IL-15R alpha mRNA suggests that IL-15 may have biological activities distinct from IL-2.