Fel d I allergen distribution in cat fur and skin.

Immunohistochemical procedures were performed to ascertain Fel d I antigen (Ag) distribution in cat fur and skin biopsy specimens and to analyze Fel d I allergen concentrations in fur. One hundred strands of fur and 24 skin biopsy specimens (6 by 4 by 3 mm) from shaved areas were collected from 11 different cats. Freshly depilated hairs were immunostained by free-floating monoclonal anti-Fel d I, avidin-biotin-peroxidase complex, and either processed for scanning electron microscopic examination or mounted on glass slides for computer-assisted densitometric analysis (SAMBA system). Skin biopsy specimens were promptly frozen and sectioned just before the immunohistochemical processing. Densitometric analysis of fur demonstrated that immunoprecipitate concentrations were tenfold higher at the root than at the tip. However, this finding may be explained by decrease of the thickness of the hair cortex that varied in similar proportions. The Ag accumulated on the strand surface but may focally penetrate into the medulla through the scale-like cortical interstices. In skin biopsy specimens, Fel d I Ag was found in epithelial squamous cells, within the epidermis and hair follicles, on the surface of the epidermis and hair follicles, and in sebaceous gland cells. These data suggest that Fel d I Ag is produced by sebaceous cells and, to a lesser extent, by basal squamous epithelial cells and that it is stored mainly on the surface of the epidermis and fur.