Staphylococcal superantigens cause lethal pulmonary disease in rabbits

Background. The Centers for Disease Control and Prevention (CDC) and others reported that methicillin-resistant S. aureus (MRSA) are significant causes of serious human infections, including pulmonary illnesses. We investigated the role played by superantigens in lung-associated lethal illness in rabbits. Methods. A rabbit model was established to investigate the potential role played by superantigens, staphylococcal enterotoxin B (SEB), staphylococcal enterotoxin C (SEC), and toxic shock syndrome toxin-1 (TSST-1). Rabbits received intrabronchial community-associated (CA) MRSA strains USA200 (TSST-1 ⁺), MW2 (SEC⁺), c99-529 (SEB⁺), or purified superantigens. Some rabbits were preimmunized against superantigens or treated with soluble high-affinity T cell receptors (Vβ-TCR) to neutralize SEB and then challenged intrabronchially with CA-MRSA or superantigens. Results. Rabbits challenged with CA-MRSA or superantigens developed fatal, pulmonary illnesses. Animals preimmunized against purified superantigens, or treated passively with Vβ-TCRs and then challenged with CA-MRSA or superantigens, survived. Lung histological analysis indicated that nonimmune animals developed lesions consistent with necrotizing pneumonia after challenge with CA-MRSA or purified superantigens. Superantigenimmune animals or animals treated with soluble Vβ-TCRs did not develop pulmonary lesions. Conclusions. Superantigens contribute to lethal pulmonary illnesses due to CA-MRSA; preexisting immunity to superantigens prevents lethality. Administration of high-affinity Vβ-TCR with specificity for SEB to nonimmune animals protects from lethal pulmonary illness resulting from SEB⁺ CA-MRSA and SEB.