Chemotactic stimuli

In examining human leukocyte responses to chemokines, donor-to-donor variation should be expected. It is not uncommon, in particular with lymphocytes, to find that 1 out of 10 donors may fail to migrate in response to any chemotactic stimuli. 

A large variety of chemicals can serve as chemotactic stimuli. Approximately 20 attractant receptors and 10 repellent receptors have been identified for Escherichia coli and Salmonella typhimurium, the two most widely-studied species (1 ). These receptors are specific for one or two chemicals at high affinities (low K ), but will also bind a range of related molecules with lower affinity (2). 

Table 4. Examples of responses to chemotactic stimuli in bacteria with flagellar motility. ...

In bacteria like E. coli and Salmonella, some chemotactic stimuli bind directly to chemotaxis-specific receptors, whereas others bind first to a primary receptor, which then interacts with a chemotaxis-specific receptor (Figure 12). The chemotaxis-specific receptors are the MCPs, mentioned in Section 5. The primary receptors are dual function in the sense that they are involved in both chemotaxis and transport of the stimulants. 

CheR, a 32 kDa soluble monomeric protein [665], is a specific methyl-transferase that, with AdoMet as a precursor, methylates the MCPs [f65, 686], In the cell, it is bound to the specific CheR/CheB-binding sequence (NWETF) at the cytoplasmic C-terminus of each of the two high-abundance receptors, Tsr and Tar [788]. From there it methylates neighboring receptor molecules, including low-abundance receptors that lack the CheR/CheB-binding site (Section 6.1.2 above). CheR is a relatively slow enzyme [665]. Its methyltransferase activity can apparently be regulated by chemotactic stimuli [369], but the mechanism is not known. 

Wymann, M.P., Kemen, R, Deranleau, D.A, Dewald, R., vonTscharner, V. and Baggiolini, M. (1987). Oscillatory motion in human neutrophils responding to chemotactic stimuli. Biochem. Biophys. Res. Commun. 147, 361-368. 

Certain components of the ion-conducting pathway have been shown to correlate with the application of chemotactic stimuli and to be missing in particular mor mutants, possessing paralysed intact flagella. It has been suggested that the mot-products may serve as ion-gates or be involved directly in energy transduction. 

The reason why AM of humans, monkeys, and dogs are predominantly directed toward interstitial sites, whereas AM of rodents are predominantly directed toward ciliated airways, remains an open question that needs further research. Intuitively, this species difference is also considered to be indicative of differences in directed migration of AM, possibly resulting from chemotactic stimuli or the distance from alveoli to terminal bronchioli according to the anatomical differences in respiratoiy bronchioli, as described in the previous section. 

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