Chemotaxis describes how bacteria and cellular organisms respond to specific chemicals in their environment.  Positive chemotaxis describes movement towards a chemical attractant, or chemoattractant; negative chemotaxis describes movement away from a chemical, or chemorepellant. An example of chemotaxis is the movement of human neutrophil cells toward an injury in response to chemical signals generated by immune system cells or invasive microbes. Chemotaxis Assay refers to the procedures and tools used to induce chemotaxis.  See Useful Links, below, for an NIH article describing chemotaxis.

Chemotaxis Assay

There are numerous methods available to assess the chemotactic activity of biological cells or organisms as well as the chemoattractant and chemorepellent properties of chemicals.  Basic measurement include:

1.    Total migration, i.e., chemotaxis

2.    Random migration, i.e., chemokinesis or chemokinetic activity (negative control)

3.    Dose response  – chemotactic response from a serial dilution of known chemoattractant

Post Migration Analysis Methods

Fluorescence Assay - e.g. Calcein, AM

Colorimetric Assay - e.g. MTT

Staining and Fixing - Polycarbonate Filter or Membrane (Wright’s stain)

Boyden chamber

A chemotaxis chamber based on a single well instrument devised by S. V. Boyden in the early 1960's.  The illustration below is an image of a Neuro Probe single well chemotaxis chamber based on Boyden’s original instrument.  A Boyden chamber is comprised of two compartments divided by a filter membrane.  The cells are positioned in the upper compartment and are induced to migrate through the filter membrane to the bottom compartment by a chemoattractant. Following incubation, the separating filter membrane is removed and stained, and the migration of cells that have moved from the upper chamber to the lower chamber of the membrane is assessed.

This process is known as Boyden chamber cell migration assay, chemotaxis assay, cell migration assay, multiwell cell migration assay as well as other variations. There are many products based on Boyden’s original device available today.

chemoattractant

A specific compound or substance with chemical properties that attracts biological cells during chemotaxis.

chemokine

A specific compound or substance that increases activity of a cell or organism. This movement may be positive, i.e., toward the chemokine, negative, i.e., away from it, or random.

chemokinesis

Term that describes increased activity of a cell or organism in response to a chemical substance.

chemokinetic controls

Areas in a chemotaxis assay where a chemotactic factor is placed at the same concentration. These are located in both the upper and the lower wells, hence, a chemoattractant is present, but there is no directional gradient in the concentration.

chemorepellent

Chemokine that induces movement away from itself. This phenomenon is also referred to as fugetaxis. May be used to inhibit or control chemoattraction