[Biological properties of a ribosomal vaccine from S. sonnei obtained by polyethylene glycol fractionation].

Shigella ribosomal vaccine was prepared by fractionation with polyethylene glycol (PEG), recently proposed as an alternative of the more expensive and labor-consuming technique of differential centrifugation. In the present investigation the biological activity of ribosomal preparations isolated by these two methods was compared. Ribosomal vaccine obtained by PEG fractionation proved to be nontoxic for mice (LD50 greater than 2 mg) and produced no local and systemic reactions in monkeys when introduced subcutaneously in a dose of 600 micrograms. Ribosomes isolated by the two methods did not differ in the antigenic potency of their O-specific component responsible for inducing antibody formation in guinea pigs and monkeys. The protective potency of Shigella ribosomal vaccines prepared by PEG fractionation and ultracentrifugation was compared by tests in guinea pigs under the conditions of intraconjunctival challenge 2 weeks after a single injection of 40-200 micrograms of ribosomes. The mean resistance rate (percentage of protected eyes) was almost the same with both preparations, 67% and 65%, while in the control (nonimmunized) group only 13% of eyes were resistant to challenge. In monkey tests two injections of ribosomal vaccine obtained by PEG fractionation ensured a high protective effect against dysentery. No clinical signs of dysentery were observed in two groups of the test animals (totaling 10 monkeys) immunized 5 and 16 weeks before oral challenge with a dose of 75 X 10(9) virulent shigellae, which caused dysentery of moderate severity in all 5 control monkeys. The low toxicity and high protective potency of ribosomes isolated from S. sonnei by PEG fractionation makes it possible to use this method for the large-scale production of ribosomal vaccine.