Stabilization of Salmonella-specific dialyzable leukocyte extracts

Some properties and protective activity of specific DLE against Salmonella cholerae suis infection

From a rabbit lymphoid tissue, twice immunized with a Salmonella ch. suis vaccine, was obtained a dialysable leucocyte extract (DLE) (m. w. 10,000Da; protein content 1.14 mg/ml; content of ribose 2.7 mg/ml; A260/A280 ratio 2.17 and pH 6.8). By gel filtration on Sephadex G-25, six peaks were obtained and activity was found in peak IV. The activity of the extract was determined by a dermo-application test (DAT) on 10 cows. The protective effect was tested by a challenge with Salmonella ch. suis and Salmonella dublin pathogen strains on white mice intraperitoneally treated with DLE. The DAT proved to be positive in 8 of the 10 cows. When applied on white mice, it induced a high specific protective effect against Salmonella ch. suis (70%), but not against Salmonella dublin infection.

Dialyzable leukocyte extract used in the prevention of Salmonella infection in calves

The protective effect of dialyzable leukocyte extract (DLE) was investigated in the experimental model of Salmonella infection in calves. DLE was obtained from the lymphatic nodes and spleens of fattening bulls immunized with whole-cell Salmonella vaccine (designated DLEs-im), from the same organs of calves immunized and subsequently infected with Salmonella typhimurium (DLEs-inf), and from non-immunized fattening bulls (DLEn). Three doses of DLEs-inf and DLEs-im applied intravenously at 3-day intervals induced protection in all calves against infection. There were statistically significant differences in the immunological, clinical and microbiological parameters. Three doses of DLEs-inf injected intramuscularly at 3-day intervals provided a protective effect; however, one calf died. The intravenous application of DLEn induced low protection against experimental Salmonella infection and two calves died. The results indicate that the preparation of antigen-specific DLE may be possible via immunization of fattening bulls.