TDI-01

The pure TdI-1 polypeptide that blocks miniature endplate potentials (MEPPs) and abolishes or reduces endplate potentials (EPPs) below the action potential threshold was identified from the crude fraction of Tityus discrepans venom. The toxin is a potent reversible non-depolarizing muscle relaxant that blocks more than 95% of the EPP at a 2 microM (0.1 mg/ml) concentration. On a molar basis, TdI-1 is as potent as or more potent than many muscle relaxants since, at the concentration used, the toxin suppressed more than 95% of the EPP. Using matrix-assisted laser desorption time of flight (MALD-TOF) ionization mass spectrometry, TdI-1 was found to have an unusally large mol. wt for a scorpion toxin, close to 48,000. The N-terminal sequence of the first 23 residues of TdI-1 was also determined. The fragment differs from the N-terminal sequences of all 140 peptidic scorpion toxins found in the SWISSPROT and PIR databases using the search engine of the felix.EMBL-Heidelberg.de computer (European Molecular Biology Laboratory, Heidelberg, Germany.

Haemagglutination inhibition and virus neutralisation antibody responses of chickens given different vaccination programmes were compared. This was followed by a further experiment in which variously vaccinated laying hens were challenged at 30 weeks of age with two strains of infectious bronchitis virus of the "variant" Dutch D207 serotype. Chickens were given primary vaccinations to different strains of infectious bronchitis live virus during rearing and then injected at 16 weeks of age with inactivated oil adjuvanted virus vaccines prepared from either M41, GV101 or both viruses combined (bivalent vaccine). Antibody titres to M41 infectious bronchitis virus were high, and to D207 serotype low. in birds given Mass type vaccines only. In birds given an initial 'priming' with Mass type live vaccine and then 'boosted' with bivalent killed vaccine, high haemagglutination inhibition and virus neutralisation antibody levels against both the M41 and D207 serotypes of infectious bronchitis virus were stimulated. In another experiment, the ability of laying hens vaccinated according to this programme, to withstand challenge with two strains of virulent infectious bronchitis virus of the D207 serotype, was tested. Protection of egg production in vaccinated hens was found to be good and in all groups correlated with the individual hen haemagglutination inhibition titre at the time of challenge. The significance of these results with regard to the use of killed virus vaccines in laying hens and to the necessity to develop live virus vaccines from 'variant' strains of infectious bronchitis virus is discussed.