Identification of membrane-associated lymphotoxin (LT) on mitogen-activated human lymphocytes using heterologous anti-LT antisera in vitro.

Surface-associated lymphotoxin (LT) molecules have been identified on mitogen-activated human lymphocytes employing heterologous anti-α-LT serum in vitro. These membrane-associated LT molecules are present on PHA- or Con A-activated lymphocytes but do not appear to be expressed on unstimulated cells. Furthermore, these molecules were detected primarily on activated T lymphocytes, with little detectable on activated B- or null-cell populations. The removal of surface LT-bearing lymphocytes, using anti-α-LT serum + C′, does not dramatically affect the capacity of the remaining cells to release LT after mitogen restimulation. In addition, the presence of toxic molecules on the surface of activated lymphocytes suggests that these materials may be expressed in an inactive, noncytotoxic form.     

Human lymphocyte function associated antigen-1 (LFA-1): identification of multiple antigenic epitopes and their relationship to CTL-mediated cytotoxicity

Human lymphocyte function-associated antigen (LFA)-1, a heterodimeric lymphocyte surface glycoprotein of 177,000 and 95,000 relative molecular weight has been implicated to function in the cytotoxic T lymphocyte (CTL) effector mechanism. Seven mouse hybridoma lines producing monoclonal antibodies (MAb) reactive with this structure were studied. Three unique and 3 partially over-lapping epitopes on human LFA-1 were defined by competitive cross inhibition binding assays using biosynthetically labeled anti-LFA-1 MAb. In contrast, of five rat antimouse LFA-1 MAb, all five recognized a common or shared epitope. An HLA-B7 specific human CTL line expressed 1.1 X 10(5) LFA-1 sites per cell with a direct saturation binding assay. Human CTL expressed two to four times more LFA-1 than peripheral blood lymphocytes or B and T lymphoblastoid cell lines. Titration of each of the anti-LFA-1 MAb in a 51chromium release cytolytic assay revealed quantitative differences in the ability of the different anti-LFA-1 MAb to block cytolysis indicating distinct functional and antigenic epitopes exist on the human LFA-1 molecule. Anti-LFA-1 MAb reversibly inhibited the CTL reaction by slowing the initial rate of cytolysis. These results suggest anti-LFA-1 MAb inhibit CTL function by specific blockade of a functionally relevant molecule.     

Serum of rabbits infected with Treponema pallidum (Nichols) inhibits in vitro transformation of normal rabbit lymphocytes.

Serum collected from outbred male New Zealand white rabbits infected intratesticularly with Treponema pallidum (Nichols) was assayed for ability to alter transformation of normal rabbit peripheral blood lymphocytes (PBL) in vitro. Sera collected from 25 infected rabbits inhibited [³H]thymidine incorporation by normal rabbit PBL stimulated with concanavalin A (Con A, 16μg/ml), relative to PBL cultured in normal rabbit serum (NRS). Maximal inhibitory activity was detected in serum collected at the time of peak orchitis. The degree of inhibition was related to the concentration of syphilitic serum in PBL cultures. Inhibition of Con A stimulation was reversed by increased mitogen concentration. Sera which depressed Con A stimulation also depressed lymphocyte transformation induced by oxidation with sodium m-periodate (NaIO₄). Cytotoxic activity was detected in occasional sera. All sera were heat inactivated at 56 °C for 30 min prior to testing. Both freshly collected sera and sera stored at ?70 °C significantly inhibited PBL transformation. These results suggested that serum of syphilitic rabbits contains one or more inhibitors of in vitro lymphocyte transformation.     

Dynamic distribution modelling of the swamp tigertail dragonfly Synthemis eustalacta (Odonata: Anisoptera: Synthemistidae) over a 20-year bushfire regime

1. Intensity and severity of bushfires in Australia have increased over the past few decades due to climate change, threatening habitat loss for numerous species. Although the impact of bushfires on vertebrates is well-documented, the corresponding effects on insect taxa are rarely examined, although they are responsible for key ecosystem functions and services. Understanding the effects of bushfire seasons on insect distributions could elucidate long-term impacts and patterns of ecosystem recovery.
2. Here, the authors investigated the effects of recent bushfires, land-cover change, and climatic variables on the distribution of a common and endemic dragonfly, the swamp tigertail (Synthemis eustalacta) (Burmeister, 1839), which inhabits forests that have recently undergone severe burning. The authors used a temporally dynamic species distribution modelling approach that incorporated 20 years of community-science data on dragonfly occurrence and predictors based on fire, land cover, and climate to make yearly predictions of suitability. The authors also compared this to an approach that combines multiple temporally static models that use annual data.
3. The authors found that for both approaches, fire-specific variables had negligible importance for the models, while the percentage of tree and non-vegetative cover were most important. The authors also found that the dynamic model outperformed the static ones, based on cross-validation omission rate. Model predictions indicated temporal variation in area and spatial arrangement of suitable habitat, but no patterns of habitat expansion, contraction, or shifting.
4. These results highlight not only the efficacy of dynamic modelling to capture spatiotemporal variables such as vegetation cover for an endemic insect species, but also provide a novel approach to mapping species distributions with sparse locality records.

     

The effects of calcium2+ and magnesium2+ on the electrophoretic mobility of chromaffin granules measured by electrophoretic light scattering

Electrophoretic light scattering was used to determine the electrophoretic mobility distributions of isolated bovine adrenal chromaffin granules as a function of divalent metal ion concentrations. Changes in the electrophoretic mobility reflected changes in the surface charge density of the granules. Ca2+ and Mg2+ (0.10--2.0 mM) were equally effective in reducing the electrophoretic mobilities. These findings are consistent with recent studies of the binding of Ca2+ and Mg2+ to the surface of chromaffin granules and are further evidence that the specific role of Ca2+ in exocytosis is due to effects other than the ability of Ca2+ to decrease the electrostatic repulsion between negatively charged membranes.     

Factors influencing production of inflorescence-derived somatic seedlings of sweetgum

Somatic embryos derived from staminate inflorescence tissues of three mature sweetgum (Liquidambar styraciflua) trees were tested for germination and conversion frequencies and early growth variables following pregermination cold treatments. Individual mature embryos were selected from repetitively embryogenic cultures maintained on Woody Plant Medium (WPM) with 1 mg l^–1 naphthaleneacetic acid and cultured on basal WPM at 10 8C for 0, 4 or 8 weeks prior to being transferred to WPM germination medium in the light. After 4 weeks, germinated embryos were planted in potting mix in an acclimatization chamber, grown for an additional 8 weeks and evaluated for conversion and growth. Conversion frequency, which ranged up to 80%, was affected by ortet and clonal line, while the number of first-order lateral roots was affected by ortet, clonal line and cold treatment, with 8 weeks of cold promoting the highest number.