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A. Armulik investigated how pericytes regulate the blood-brain barrier. In the 2010 mouse study, pericyte-deficient mutants showed increased passage of tracers across brain vessels. The increased permeability involved endothelial transcytosis; the study also linked pericytes to endothelial gene-expression patterns and polarization of astrocyte end-feet.^[ref]

This makes an important mechanistic distinction: a barrier depends on regulated transport through cells as well as seals between cells. Measuring tracer escape and identifying the route of escape answer different experimental questions. The primary paper identifies the author as Annika Armulik.

A pericyte is a vessel-associated biological cell located along the outside of small blood vessels, closely associated with endothelial cells. Pericytes help regulate vessel maturation and barrier properties. In mice with reduced pericyte coverage, vascular permeability and transport across the blood-brain barrier change; this connects a surrounding support cell to the function of the endothelial cell barrier. Coverage, anatomical location and functional evidence should be considered together when identifying pericytes. ^[ref]