Figure 1. A dual role for nociceptors. Bacteria release factors, such as N-formyl-methionyl-isoleucyl-phenylalanine-leucine (FMIFL) and a-hemolysin (aHL), that directly stimulate nerve fibers [a] and produce action potentials in two directions [b]. In one direction, action potentials travel toward the spinal cord and send pain messages to the brain [c(1)]. In the other direction, they travel toward the periphery, causing the release of neuropeptides [c(2)]. The neuropeptides inhibit the activation of immune cells [d(2)], decreasing their ability to clear the bacteria [e(2)] and showing an immune-suppressive role for nociceptors that accompanies their role in pain transmission.