CD4 and peritonitis: Taken together, the results presented in this study demonstrated that rationally designed first generation 4C-Staph vaccine, formulated with alum or MF59, two adjuvants licensed in human vaccines, induced persistent protection, albeit partial, in an animal model of S. aureus-induced peritonitis, and that 4C-Staph-specific antibodies and CD4 T cells contributed to the protective mechanisms.