Chemotaxis

Chemotaxis is the movement of a cell or organism towards a stimulus, usually along the gradient of a diffusible chemical signal. It must be distinguished from chemokinesis, where the movement is not directed.

A classical example is the movement of a polymorphonuclear leukocyte towards an area of acute inflammation. The neutrophil concentrates receptors for a given substance towards the leading margin of its surface membrane. The receptors can be for a variety of substances:

• bacterial factors e.g. simple peptides, prostaglandins
• components of complement system e.g. C5a
• endogenous arachidonic acid metabolites e.g. leukotriene B4 All may be produced by acute inflammation. The signal is transduced across the cell membrane to secondary chemical messenger systems internally; interpretation of differences between regions of the membrane permit reorientation of the internal cytoskeleton to produce movement in a given direction.