Chemotaxis assay

In general, the most important requisite is to calibrate the incubation time of the assay both to the model cell and the ligand to be evaluated.

Some variations of the technique deal also with wells and parallel channels connected by a cut at the start of the experiment (PP-technique).

Radial arrangement of PP-technique (3 or more channels) provides the possibility to compare chemotactic activity of different cell populations or study preference between ligands.

For modelling in vivo conditions, several protocols prefer coverage of filter with molecules of extracellular matrix (collagen, elastin etc.)

Besides the above-mentioned two most commonly used family of techniques, a wide range of protocols were developed to measure chemotactic activity.

Some of them are only qualitative, like aggregation tests, where small pieces of agar or filters are placed onto a slide and accumulation of cells around is measured.

In another semiquantitative technique, cells are overlaid the test substance and changes in opalescence of the originally cell-free compartment is recorded during the incubation time.

The process of chemotaxis can be demonstrated using a capillary tube assay (shown above). The motile prokaryotes can sense chemicals in their environment and change their motility accordingly. When no chemicals are present, movement is completely random. When a repellent or attractant chemical is present, the motility changes; runs become longer and tumbles become less frequent so that the net movement towards or away from the chemical can be achieved. The net movement can be seen in the beaker, where the bacteria accumulate around the attractant, and away from the repellent. The beaker used in this illustration is from Wikimedia Commons - " Laboratory Glassware - Beaker " by Amanda44.
Chemotaxis assays with agar plates
Chemotaxis chamber assays
Other chemotaxis assay techniques