Recombinant protein Bd37 protected gerbils against heterologous challenges with isolates of Babesia divergens polymorphic for the bd37 gene.

The Bd37gene encoding for a glycosyl-phosphatidyl-inositol anchored protein of Babesia divergens displays genetic polymorphisms among isolates. Five major polymorphic groups (clades) were shown by PCR-RFLP among different B. divergens isolates. Each group has been characterized according to a reference Bd37 gene (Rouen87, W8843, Y5, 6303E and 1705B). Recombinant (GST fusion) protein (Bd37r) expressed from the Bd37 gene, was used as antigen in a saponin-based formulation and was able to protect gerbils, after 2 injections at low dose vaccine concentration (1 mug per dose), against a virulent challenge with the B. divergens Rouen87 isolate. In spite of polymorphism of Bd37 gene, Bd37r induced complete immunoprotection against challenges with each of the 5 reference isolate groups defined by PCR-RFLP.

Association between sequence polymorphism in an epitope of Babesia divergens Bd37 exoantigen and protection induced by passive transfer.

In Europe, Babesia divergens is the major agent responsible for babesiosis in cattle and can occasionally infect splenectomised humans. Recently, we reported the characterisation of a 37 kDa exoantigen (Bd37) anchored in the merozoite membrane of B. divergens by a glycosylphosphatidyl-inositol. After phospholipase hydrolyse of the glycosylphosphatidyl-inositol anchor, the Bd37 antigen could be isolated in the plasma of the infected host and from the in vitro culture supernatants. Immunisation of mice with a gel-filtration protective fraction of B. divergens exoantigens, produced a monoclonal antibody (MAb), called F4.2F8-INT, directed against Bd37. In the present study, we report data on passive protection using MAb F4.2F8-INT. This MAb was able to completely protect against virulent challenges with B. divergens isolates Rouen 1987 (Rouen87) and Weybridge 8843 (W8843) but had no protective effect against another French isolate from Massif Central (6303E). Physical characterisation of the epitope recognised by F4.2F8-INT allowed us to explain the differences observed between these isolates by western blotting and passive protection. These results suggest that the antigen carrying this epitope could be used as a target in the development of a recombinant vaccine against B. divergens babesiosis.

Different mechanisms involved in relaxation of guinea-pig trachea by endothelin-1 and -3.

The effects of endothelin-1 and endothelin-3 were investigated on carbachol-contracted guinea-pig isolated trachea. Endothelin-1 and endothelin-3 (0.1-100 nM) induced partial dose-dependent relaxation of the precontracted preparations. The endothelin-1-induced relaxation was markedly attenuated by haemoglobin (10 microM) and methylene blue (10 microM) and by epithelium removal. In contrast, endothelin-3-induced relaxation was not affected by haemoglobin, methylene blue or epithelium removal. The large conductance Ca(2+)-activated K(+)-channel blocker, charybdotoxin, antagonized the endothelin-1- and the endothelin-3-induced relaxation to the same extent. These results show that both endothelin-1 and endothelin-3 relaxant activities are modulated by charybdotoxin-sensitive K(+)-channels, while the nitric oxide pathway is only involved in endothelin-1 relaxant effects.

Endothelin-1 and endothelin-3 relax isolated guinea pig trachea through different mechanisms.

The effects of endothelin-1 (ET-1) and endothelin-3 (ET-3) were investigated on carbachol-contracted guinea-pig trachea. ET-1 and ET-3 induced a dose-dependent relaxation of the precontracted preparations. ET-1-induced relaxation was attenuated by hemoglobin and methylene blue. By contrast, ET-3-induced relaxation was not affected by hemoglobin or methylene blue. The large conductance Ca(2+)-activated K(+)-channel blocker charybdotoxin antagonized ET-1- and ET-3-induced relaxations. These results show that charybdotoxin-sensitive K+ channels are involved in both ET-1 and ET-3 relaxant activities, whereas the nitric oxide pathway is involved only in ET-1 relaxant effects.

Cardiovascular effects of SCA40, a novel potassium channel opener, in rats.

1. Experiments have been performed to investigate the cardiovascular actions in the rat of SCA40, a novel potassium channel opener which is a potent relaxant of guinea-pig airway smooth muscle in vivo and in vitro. 2. SCA40 (0.01-30 microM) caused a complete and concentration-dependent relaxation of rat isolated thoracic aorta contracted with 20 mM KCl but failed to inhibit completely the spasmogenic effects of 80 mM KCl. 3. The ATP-sensitive K(+)-channel blocker, glibenclamide (3 microM), failed to antagonize the relaxant action of SCA40 on 20 mM KCl-contracted rat isolated thoracic aorta. 4. SCA40 (0.001-100 microM) had dual effects on rat isolated atria. At low concentrations, SCA40 produced a concentration-dependent decrease in the rate and force of contractions. At higher concentrations (greater than 1 microM) SCA40 induced concentration-dependent increases of atrial rate and force. 5. In vivo, in normotensive Wistar rats, SCA40 elicited a dose-dependent (1-100 micrograms kg-1) decrease in mean arterial pressure which was accompanied by a moderate dose-dependent increase in heart rate. SCA40 (100 micrograms kg-1) had a slightly greater hypotensive effect than cromakalim (100 micrograms kg-1) but the duration of the hypotension was longer with cromakalim than with SCA40. 6. The hypotensive effect of SCA40 was not reduced by propranolol, atropine, NG-nitro-L-arginine methyl ester (L-NAME) or glibenclamide. 7. It is concluded that the mechanism by with SCA40 relaxes vascular smooth muscle in vitro and in vivo involves activation of K(+)-channels distinct from glibenclamide-sensitive ATP-sensitive K(+)-channels.