This is an image of actin comet tails (red) formed by beads (blue) coated with the WASP protein, which is the product of the gene mutated in the human disease Wistkott-Aldrich Syndrome. This X-linked disease generally affects boys, and causes clinical manifestations including immune deficiency, reduced number of blood platelets, and eczema. A key function of the WASP protein is to promote actin polymerization and facilitate signal transduction in immune cells such as T- and B-lymphocytes.