Phenotypic characteristics of peripheral blood T cells regulating colony growth by nontransformed human B lymphocytes

The phenotypic characteristics of peripheral blood T cell subpopulations regulating human B cell colony growth stimulated by Staph protein A were investigated. Colony growth was facilitated by OKT4 cells, and T cells expressing DR antigens were found to be partially responsible for colony facilitation. A linear increase in the magnitude of colony growth was observed with greater T cell numbers, and maximal colony enhancement occurred when T cells were present during the early stages of colony formation. OKT8 cells did not enhance colony growth and also inhibited the facilitation of colony formation by OKT4 cells. Other experiments showed that the functional activities of OKT4 and OKT8 cells differed in their requirements for DNA synthesis. Although active T cell DNA synthesis was absolutely required for the facilitation of colony growth at all concentrations tested, DNA synthesis was not needed for OKT8 inhibition of OKT4 promotion of colony formation. Thus, distinct T cell subsets whose functional properties differ in their requirements for DNA synthesis regulate human colony growth.     

Comparative effects of trichothecene mycotoxins on bovine platelet function: Acetyl T-2 toxin,a more potent inhibitor than T-2 toxin

The effects of the trichothecene mycotoxins (acetyl T-2 toxin, T-2 toxin, HT-2 toxin, palmityl T-2 toxin, diacetoxyscirpenol (DAS), deoxynivalenol (DON), and T-2 tetraol) on bovine platelet function were examined in homologous plasma stimulated with platelet activating factor (PAF). The mycotoxins inhibited platelet function with the following order of potency: acetyl T-2 toxin > palmityl T-2 toxin = DAS > HT-2 toxin = T-2 toxin. While T-2 tetraol was completely ineffective as an inhibitor, DON exhibited minimal inhibitory activity at concentrations above 10×10^?4M. The stability of the platelet aggregates formed was significantly reduced in all mycotoxin treated platelets compared to that of the untreated PAF controls. It is suggested that the increased sensitivity of PAF stimulated bovine platelets to the more lipophilic mycotoxins may be related to their more efficient partitioning into the platelet membrane compared to the more hydrophilic compounds.     

Active and passive cation transport and L antigen hertogeneity in low potassium sheep red cells

Several lines of experimental evidence are presented suggesting that the L antigens in low potassium (LK) sheep red cells are associated with separate Na(+)K(+) pump flux is distinct from the action of anti-L(l) on K(+) leak flux, implying that K(+) leak transport sites may not be converted into active pumps by the L antiserum. Treatment of LK red cells with trypsin completely abolished both the stimulation of K(+) pump flux and the enhancement of the rate of ouabain binding brought about by anti- L. That this effect is due to a total destruction of the L(p) determinant associated with the LK pump was evident from the complete failure of anti-L(p) to bind to trypsinized LK red cells. The L(p) antigen can be effectively protected against the trypsin attack by prior incubation with anti-L, indicating that the sites for antibody binding and trypsin action may be closely adjacent at the structural level. Trypsin treatment, however, did not interfere with anti-L(l) reducing ouabain insensitive K(+) leak influx, nor did it prevent binding of anti-L(ly), the hemolytically active L antibody which is probably identical with anti-L(l). The functional independence of the L(p) and L(l) sites was documented by the observation that anti-L(l) still reduced K(+) leak influx in LK cells with experimentally induced high potassium concentrations, at which K(+) pump flux is fully suppressed, whether or not anti-L(p) was binding to the L(p) antigen associated with the LK pump.     

Characteristics and differential T-cell dependency of human B-cell colony precursors

Studies were performed to characterize the human peripheral blood non-T cells forming colonies in semisolid cultures stimulated with Staph protein A (SpA). Negative selection experiments revealed that colony precursors largely consisted of cells bearing Fc receptors, complement receptors (CR), surface immunoglobulin (sIg), and Ia-like antigens. Most colony precursors expressed sIgM and sIgD, but not sIgG. Also, colony-forming cells were shown to be distinct from non-T cells proliferating in SpA-stimulated liquid cultures as evidenced by the greater sensitivity of colony precursors to anti-K,λ, or -Ia plus complement depletion. Two distinct categories of colony-forming cells could be distinguished by the expression of CR. CR-positive cells were responsible for greater than 85% of the colonies formed in the absence of optimal T cell numbers. Although under identical conditions CR^? cells demonstrated minimal colony growth, the addition of optimal T cell numbers significantly augmented colony responses. Thus, colony precursors express surface markers characteristic of B cells relatively advanced in the developmental pathway. However, less advanced cells are capable of colony growth in the presence of optimal T cell numbers.     

Tolerance to imidazolinone herbicides in wheat

An imidazolinone-tolerant wheat (Triticum aestivum L. em Thell) mutant in the winter wheat cultivar Fidel has been identified and characterized. The mutant was isolated from a population derived through seed mutagenesis of the variety with an aqueous solution containing sodium azide. Imidazolinone-tolerant wheat seedlings were selected from the M₂ generation of the population in the presence of imazethapyr herbicide and identified as herbicide-insensitive individuals. The trait is inherited as a single semidominant gene and confers high levels of tolerance to imazethapyr. Acetohydroxyacid synthase activity in extracts from imidazolinonetolerant plants was less inhibited by imazethapyr than the enzyme from the wild type. The herbicide-tolerant plants have a completely normal phenotype and display no negative effects on growth and yield in either the absence or presence of imazethapyr.     

Cellular characteristics and specificity of alloactivated regulatory T cells modulating T-cell-mediated responses

The characteristics of human alloactivated regulatory T (T_r) cells influencing the proliferative responses of mixed lymphocyte reactions (MLR) were analyzed based on relative major histocompatibility complex (MHC) specificity, proliferative requirements, Fc receptor expression, and buoyant density. Optimal T_r-mediated suppression required MHC homology with the responder, but not the stimulator populations. In addition, T_r suppression consisted of both proliferative and nonproliferative components. By either Fc receptors for immunoglobulin G (IgG) (Tγ) or buoyant density, no precursor populations predestined to differentiate into specific T_r subpopulations could be delineated. However, fractionation of the T_r populations by buoyant density demonstrated slowly sedimenting suppressor subpopulations and rapidly sedimenting amplifier cells with the net effect representing a balance among these differing functional subpopulations. Finally, the T_r suppressive populations failed to demonstrate FcIgG surface receptors therefore indicating that both T-γ and T non-γ subpopulations are capable of differentiating into alloactivated T non-γ suppressor cells.     

Globins Synthesize the Second Messenger Bis-(3′-5′)-Cyclic Diguanosine Monophosphate in Bacteria

Globin-coupled sensors are heme-binding signal transducers in Bacteria and Archaea in which an N-terminal globin controls the activity of a variable C-terminal domain. Here, we report that BpeGReg, a globin-coupled diguanylate cyclase from the whooping cough pathogen Bordetella pertussis, synthesizes the second messenger bis-(3′-5′)-cyclic diguanosine monophosphate (c-di-GMP) upon oxygen binding. Expression of BpeGReg in Salmonella typhimurium enhances biofilm formation, while knockout of the BpeGReg gene of B. pertussis results in decreased biofilm formation. These results represent the first identification a signal ligand for any diguanylate cyclase and provide definitive experimental evidence that a globin-coupled sensor regulates c-di-GMP synthesis and biofilm formation. We propose that the synthesis of c-di-GMP by globin sensors is a widespread phenomenon in bacteria.     

Molecular dynamics study of hell’s gate globin I (HGbI) from a methanotrophic extremophile: oxygen migration through a large cavity

Hell’s gate globin I (HGbI), a heme-containing protein from the extremophile Methylacidiphilum infernorum, has fast oxygen-binding/slow release characteristics due to its distal residues Gln and Tyr. The combination of Gln/Tyr distal iron coordination, adaptation to extreme environmental conditions, and lack of a D helix suggests that ligand migration in HGbI differs from other previously studied globins. Locally enhanced molecular dynamics trajectories of oxygen migration indicate a large internal cavity. This may increase the tendency of oxygen to exit from portals other than the most direct exit from the space near the heme. Oxygen may reside transiently in shallow surface depressions around the exits. Such surface trapping may enhance both oxygen uptake by increasing contact time between molecules, and decrease release by increasing the probability of oxygen reentry from the vicinity of the portal.