Chemotaxis chemoattractants

Figure 4.10. Changes in cell shape during phagocytosis and chemotaxis. Both of these neutrophil functions require protrusion of pseudopodia (either to engulf the bacterium or else to move the cell along a chemoattractant gradient) followed by contraction.

Neutrophils may move at speeds of up to 20 /tm min-1 in response to chemoattractants such as denatured proteins, lipids, peptides or C5a. Movement may be defined either as chemokinesis, which is generalised (non-directional) locomotive activity, or as chemotaxis, which is orientation and directional migration up a concentration gradient. A concentration difference at opposite ends of the cell of only 1% is sufficient to activate such directional movement. However, neutrophils do not respond chemotactical-ly to static gradients of chemoattractants, and both temporal and directional changes in chemoattractant concentrations are required. 

Molecules (chemoattractants) that stimulate neutrophil-directed migration (chemotaxis) bind to distinct receptors on neutrophil plasma membranes (discussed in Chapter 38 of this text). Within seconds after chemoattractant binding, neutrophils exhibit rapid oscillations in actin polymerization and depolymerization (12,13). The shape changes accompanying chemoattractant binding depend on the duration and extent of F-actin polymerization (3). These quantitative studies of F-actin content were performed utilizing a flow cytometric assay that detects the fluorescence intensity of individual, fixed, permeabihzed cells that have been stained with F-actin-specific, fluorescent phallotoxins (14,15). 

It is important to examine the fluorescent conjugate for biological activity and confirm that the coupling procedure does not destroy the chemoattractant stimulatory activity. We evaluate neutrophil chemotaxis in a 48-well micro-chemotaxis chamber (7) as previously described in detail (8) and briefly outlined below. 

Pipet -25 pL of chemoattractant in each lower well of the chemotaxis chamber. 

Chemoattractant cytokines soluble factors that induce chemotaxis of lymphocytes. 

IL-16. IL-16 was originally described as a lymphocyte chemoattractant factor (C4). It is produced by CD8+ T cells upon induction of lectins, histamine, or serotonin (LI). It is also produced by CD4+ T cells stimulated with lectins, antigen, or anti-CD3 antibodies (C5) and from eosinophils (L13), epithelial cells (C5), and mast cells (R8). Recently, IL-16 has been found to induce eosinophil chemotaxis (CIO), and plasma IL-16 is elevated in allergic rhinitis (PH). 

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