Why antibodies disobey the Hippocratic Oath and end up doing harm: a new clue.

The appearance of methicillin-resistant Staphylococcus aureus (MRSA) as an endemic microbe, first in hospital and health care settings and more recently in the community, has led to a disastrous situation in which use of the available antibiotic armamentarium is increasingly ineffective and spawns further antibiotic resistance. This vicious cycle highlights the pressing need for an S. aureus vaccine. However, to date, clinical trials with S. aureus vaccines have not demonstrated sustained efficacy. In this issue of the JCI, Skurnik and colleagues report that specific antibodies to two different S. aureus surface polysaccharides, which independently promote effector cell killing of S. aureus in vitro and protection against S. aureus in animal models, bind to and abrogate the activity of one another when they are combined. This fascinating finding suggests a new paradigm to explain the failure of antibody immunity to S. aureus.