Background: Ultrastructural studies of the hair follicle show that the outer root sheath (ORS) does not consist of a homogeneous cell population. The innermost cell layer of the ORS, also called the companion layer, is a single cell layer closely associated with the Henle layer of the inner root sheath.
Objectives: To describe the immunohistochemical expression of calretinin, a calcium-binding protein, in the human hair follicle.
Methods: Immunohistochemical studies using two different antisera to calretinin were performed in paraffin-embedded and in frozen scalp specimens using standard techniques.
Results: Calretinin immunostaining was consistently and specifically found in the companion cell layer of hair follicles.
Conclusions: These findings provide further evidence to support the notion that the companion layer is not only morphologically, but also immunohistochemically, different from the other cells of the ORS.