Leukocyte chemotaxis.

Monocyte chemotaxis is a function of mononuclear phagocytic system cells that enables migration toward the focus of infection and inhibition of microorganism growth and proliferation. In this paper we review the chemotactic phenomena following Becker's scheme that distinguishes three phases: recognition, transduction and the effector phase. The recognition phase is comprised of the interaction of a chemotactic agent with a receptor located on the cell surface. We cite the multiple chemoattractant presently known, and the mechanisms that regulate this phase, "up-regulation" and "down-regulation" phenomena, and the presence of receptors in low and high-affinity states. The transduction phase comprises all biochemical events produced after internalization of the attractant-receptor complex, whose purpose is triggering the cell motor apparatus. The key event in beginning movement is the increase of cytosol calcium. Alterations in membrane phosphoinositols constitute the initial transductor mechanism in chemotaxis, inositol-triphosphate and diacylglycerol behaving as second messengers. We review the diverse functions of these phospholipids, as well as we do a graphic representation of these (fig 1). Motor phase comprises the movement of the cell toward the chemotactic gradient through activation of the motor cell apparatus. We describe the intervening elements, actin and its regulatory proteins acumentin and gelsolin, actin-fixing protein, myosin and microtubuli, and the four phases of locomotion mechanism: reversible adherence, pseudopode emission, cell polarity and movement that results from an alternance between gel and sol states.