Purified Immunoglobulin F(ab′)2 Prevents Lethal Staphylococcal Enterotoxin B Intoxication in Mice and Rhesus Monkeys

Objective: Staphylococcal enterotoxin B (SEB), an exotoxin produced by single- or multi-drug-resistant Staphylococcus aureus (S. aureus), can induce food poisoning and toxic shock syndrome. Because no treatment is available for SEB-poisoned patients, development of a safe and effective SEB antidote is urgently needed. Methods: First, SEB was prepared, and native SEB (nSEB) was used to construct lethal mouse and rhesus monkey models. Second, F(ab′)2 fragments of IgG antibodies were cleaved with pepsin from horses inoculated with Freund’s adjuvant-purified nSEB. Finally, protective efficacy was evaluated in mouse and rhesus monkey models of lethal SEB intoxication. Results: In mouse and monkey model studies, the purity of the prepared nSEB reached 90%, and that of the F(ab′)2 fragments reached 83.09%. In mice and rhesus monkeys, the median lethal dose (LD50) of staphylococcal enterotoxin B (SEB) was 21.87 μg/kg and 23.77 μg/kg, respectively. Additionally, administration of 6.25 mg/kg and 7.125 mg/kg of F(ab′)2 fragments, respectively, effectively prevented SEB-induced lethality. Finally, single-cell sequencing of peripheral blood immune cells was used to detect the effects of the therapeutic antibody on peripheral blood immune cells. The underlying mechanism was found to involve inhibition of neutrophil activation, proliferation, and differentiation. Conclusions: Purified F(ab′)2 fragments were an effective antidote to lethal SEB doses in mice and rhesus monkeys, and therefore might be a favorable candidate for treating patients with severe SEB intoxication.