Immunological studies in mice with swine edema disease principle (neurotoxin)

The pathogenesis of edema disease in pigs. A review

Edema disease is known to cause important losses in the period shortly after weaning. Although the disease is known for many decades, intensive studies with bacterial lysates of pathogenic E. coli, followed by biotechnological research the last ten years, has led to a better understanding of its pathogenesis. Especially the impact of the toxin is clearly established. Evidence also exists that adhesion factors play a crucial role in the pathogenesis of edema disease.

Immunization of pigs with a purified Shiga-like toxin II variant toxoid

Passive transfer of neutralizing antibodies and active immunization with a toxoid of purified Shiga-like toxin II variant (SLT-IIv, edema disease toxin) were used to protect pigs against challenge with SLT-IIv. Six 6-week-old pigs were passively immunized by intraperitoneal administration of an immunoglobulin preparation from porcine antiserum against purified SLT-IIv. Six 6-week-old pigs and twelve 2-week-old pigs were actively immunized by two intramuscular injections of 25 micrograms of SLT-IIv toxoid given 2 weeks apart. The 24 immunized pigs and an equal number of age-matched unimmunized control pigs were all challenged by intravenous injection of purified SLT-IIv (6 ng/kg body weight). The six passively immunized pigs acquired neutralizing SLT-IIv antibody titers of 1280 or 2560 and the 18 actively immunized pigs mounted a serum immune response with toxin neutralizing titers ranging from 128 to 10,240. All 24 immunized pigs survived the challenge but nine pigs with the lowest titers showed mild clinical signs of edema disease. All 24 control pigs died within 30 hours of challenge.

Reproduction of edema disease of swine with purified Shiga-like toxin-II variant

Twenty-one weaned Yorkshire-Landrace pigs were injected intravenously with graded doses of purified Shiga-like toxin-II variant (edema disease toxin). In a preliminary study, three pigs (Nos. 1, 2, 3) were injected with 48, 24, and 12 ng, respectively, of SLT-IIv/kg of body weight. Subsequently, three groups (Nos. 4, 5, 6) of six pigs each were injected with 6, 3, and 1.5 ng, respectively, of SLT-IIv/kg of body weight. Severe clinical signs and histologic lesions characteristic of edema disease developed in pigs Nos. 1, 2, and 3, and all six pigs in group No. 4. Eight of these pigs were euthanatized in extremis (mean time to death was 34 hours) and one died of the disease (52 hours). Moderate signs and lesions of edema disease were observed in all pigs in group No. 5, and three pigs were euthanatized (mean time to euthanasia was 42 hours). Mild signs and lesions were observed in three pigs in group No. 6. The most common gross pathologic changes were edema of the eyelids, submucosa of the stomach, and mesentery of the spiral colon and hemorrhage of the colon and cerebellum. Microscopic lesions were associated with vascular injury and included vessel necrosis, perivascular edema and hemorrhage, and superficial colonic and cecal erosions. The vascular lesions were observed in the cerebellar folia, submucosa and mucosa of the stomach, cecum, colon, and sporadically in the retina. None of the clinical signs associated with endotoxin were observed.

Purification and characterization of an Escherichia coli Shiga-like toxin II variant

A Shiga-like toxin II variant was purified to homogeneity from Escherichia coli TB1(pCG6), which contained the toxin genes cloned in multicopy plasmid pUC18. The purification scheme involved polymyxin B extraction of the toxin from bacterial cells, followed by differential (NH4)2SO4 precipitation, anion- and cation-exchange fast-protein liquid chromatography, and immunoaffinity exclusion chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified toxin revealed three protein bands that migrated with calculated molecular weights of 33,000, 27,500, and 7,500. These bands correspond to values for the A, A1, and B subunits, respectively, that would be expected on the basis of the nucleotide sequence and comparison with data for Shiga toxin and other Shiga-like toxins. Electrophoresis under nonreducing conditions resulted in disappearance of the 27,000-molecular-weight band. Western blot (immunoblot) analysis revealed three protein bands with molecular weights of 33,000, 27,500, and 7,500. The purified toxin induced typical signs of edema disease in pigs injected intravenously with doses as small as 3 ng/kg of body weight. The 50% cytotoxic doses for Vero, PK15, and Madin-Darby bovine and canine kidney cells were 0.5, 2.0, 8.0, and 8.0 pg, respectively. The 50% lethal dose of purified toxin for mice was 0.9 pg by the intraperitoneal route. Approximately 75 micrograms of purified toxin was required to induce a 1-ml/cm fluid response in rabbit ileal loops. Antiserum to the Shiga-like toxin II variant neutralized homologous toxin, Shiga-like toxin II, and Verotoxin 2 but not Shiga-like toxin I.