After incubation, cell-free supernatants were collected and assayed for TNF concentrations by using a solid-phase sandwich enzyme-linked immunosorbent assay as specified by the manufacturer (eBioscience, San Diego, CA). TNF is a key cytokine produced by macrophages during MRSA stimulation. In our preliminary studies, we also measured secretion of other cytokines and found that IL-1, IL-6, and NO secretion were strongly correlated with TNF secretion in response to these bacteria (r 2 = 0.84, 0.87 and 0.93, respectively). We focused on TNF secretion for these studies.