Receptors that mediate this process trigger both a fast, excitatory signal and a slow, inhibitory signal according to the LEGI model. Receptors that facilitate this process are divided into three families based on whether there are 0, 1, or 3 amino acids between their two N-terminal cysteines. Pro-inflammatory formyl peptides like fMLF mediate pattern recognition and this process. Leu·ko·tri·ene B4, complement protein 5a, and inter·leu·kin 8 are the main mediators of this process in neutrophils. HIV (*) enters T-cells and macrophages by hijacking two co-receptors that mediate this process, called CCR5 and CXCR4. (10[1]-5[1])Many immune cells use a gradient-sensing form of this process to target sites of foreign invasion. For 10 points, name this process in which a cell moves in response to a chemical stimulus. ■END■ (10[1])