Immunologic tolerance to allergenic protein determinants: properties of tolerance induced in mice treated with conjugates of protein and a synthetic copolymer of D-glutamic acid and D-lysine (D-GL).

Conjugates of proteins and the synthetic copolymer of D-glutamic acid and D-lysine (protein-D-GL) reproducibly induce significant unresponsiveness to the protein antigens in experimental mice. Proteins studied include ovalbumin and antigen E of ragweed extract, the major allergen of ragweed pollen. The unresponsive state 1) can be induced in both unsensitized and previously sensitized experimental animals, 2) is selectively confined to responses of the IgE antibody class, 3) is long lasting, and 4) is highly antigen specific. IgE antibody responses can also be suppressed by administering comparable doses of unconjugated protein alone; however, the unresponsive state induced in this manner is only transient and rebound production of IgE antibody is often observed. Results from the studies of the cellular basis of the protein-D-GL induced unresponsiveness demonstrate that 1) protein-D-GL conjugates do not induce unresponsiveness at the level of protein-specific B cells, 2) tolerance is not induced by virtue of a detectable antigen-specific suppressor T cell mechanism, 3) tolerance is most probably induced in the antigen-specific helper T cell populations. The significant IgE-selective and antigen-specific tolerogenic activity of protein-D-GL conjugates make these compounds potential candidates for use as therapeutic agents in the treatment of IgE-mediated human allergic disorders induced by protein allergens.     

The optimum pH of renal adenosine triphosphatase and its variation with the type of ATP.

The in vitro optimum pH of renal (Na+, K+)-ATPase, assumed to be 7.8, depends on the type of ATP used. The accepted value is obtained with 'grade II' ATP but with purer ATP ('Sigma grade') it lies close to the intracellular pH in rat medulla and cortex (pH 7.0, 7.2). Values were identical in rats subjected to dietary potassium depletion for 2-4 weeks. The optimal Mg2+ concentration was also influenced by the type of ATP but Mg ATPase activity was unaffected. Both types of ATP were hydrolysed by trichloracetic acid. Where the purer ATP is used the assay conditions need to be modified accordingly.     

The effect of luteinizing hormone releasing hormone (LRH) on pituitary gonadotropins in male homosexuals.

Basal serum LH and FSH values were found to be within normal limits in 9 homosexual men. The mean LH and FSH responses following the intravenous administration of 100 microgram of LRH were not significantly different from that of heterosexual controls. In addition, the mean basal plasma serum testosterone was similar in the two groups. There is thus no definite implication of endocrine factors in the genesis of male homosexuality.     

Radiosensitivity parameters for neoplastic transformations in C3H10T1/2 cells

We have evaluated radiosensitivity parameters for cellular transformation from published experimental data on neoplastic transformations induced in C3H10T1/2 cells by BEVALAC ions. The measured RBE values are well reproduced by a track theory calculation using sets of m-target parameters with either m = 2 or m = 3, suggesting a quadratic or cubic extrapolation to low doses of gamma rays. Using track theory one is thus able to predict transformation frequencies in those cells after an arbitrary radiation field, under known or assumed conditions of exposure, in a manner shown earlier for cellular survival. Extension of these calculations to interpret cancer incidence in vivo is also discussed.     

Deletion of the C-terminus of polynucleotide phosphorylase increases twitching motility, a virulence characteristic of the anaerobic bacterial pathogen Dichelobacter nodosus

The Gram-negative anaerobe Dichelobacter nodosus is the causative agent of footrot in sheep. Different strains of D. nodosus cause disease of differing severities, ranging from benign to virulent. Virulent strains have greater twitching motility and secrete proteases that are more thermostable than those secreted by benign strains. We have identified polynucleotide phosphorylase (PNPase) as a putative virulence regulator and have proposed that PNPase expression is modulated by the adjacent integration of genetic elements. In this study, we compared PNPase activity in three virulent and four benign strains of D. nodosus and found that PNPase activity is lower in virulent strains. We disrupted the pnpA gene in three benign D. nodosus strains and two virulent strains and showed that deletion of the S1 domain of PNPase reduced catalytic activity. In all but one case, deletion of the PNPase S1 domain had no effect on the thermostability of extracellular proteases. However, this deletion resulted in an increase in twitching motility in benign, but not in virulent strains. Reconstruction of the pnpA gene in two mutant benign strains reduced twitching motility to the parental level. These results support the hypothesis that PNPase is a virulence repressor in benign strains of D. nodosus .     

Metabolism of AGEs – Bacterial AGEs Are Degraded by Metallo-Proteases

Advanced Glycation End Products (AGEs) are the final products of non-enzymatic protein glycation that results in loss of protein structure and function. We have previously shown that in E. coli AGEs are continually formed as high-molecular weight protein complexes. Moreover, we showed that AGEs are removed from the cells by an active, ATP-dependent secretion and that these secreted molecules have low molecular weight. Taken together, these results indicate that E. coli contains a fraction of low molecular weight AGEs, in addition to the high-molecular weight AGEs. Here we show that the low-molecular weight AGEs originate from high-molecular weight AGEs by proteolytic degradation. Results of in-vitro and in vivo experiments indicated that this degradation is carried out not by the major ATP-dependent proteases that are responsible for the main part of bacterial protein quality control but by an alternative metal-dependent proteolysis. This proteolytic reaction is essential for the further secretion of AGEs from the cells. As the biochemical reactions involving AGEs are not yet understood, the implication of a metalloprotease in breakdown of high molecular weight AGEs and their secretion constitutes an important step in the understanding of AGEs metabolism.