Follicular keratinization

Abstract

Autoradiographic studies showed that comedones in acne vulgaris result from 2 abnormalities in keratinization: increased formation of horny cells, and increased cohesion among these cells. In open comedones, the cellular contents are eventually sloughed through the wide opening, but in closed comedones few cells can squeeze through the tiny orifice. The experiments described in this article were designed to extend these studies and to stimulate follicular or comedonal epithelia so that the patterns of keratinization could be observed with light microscopy. The purpose of this investigation was to observe patterns of keratinization induced experimentally. Since acne surgery (comedo removal) is widely used in therapy, the refilling, repair, and regeneration of comedones after such removal needed to be studied. Lowney et al. have already reported 2 clinical observations after comedo removal. Removal of the entire core without recurrence is most desirable and may be the result of several events: full evulsion of the comedo epithelium, prolapse of the epithelium which becomes necrotic and is sloughed off; and scar formation with a comedo like retention hyperkeratosis. The basic requirement for healing, i.e., true reconversion of a comedo into a normal sebaceous follicle, which has been presumed by many but never convincingly demonstrated, was occasionally seen in patients after comedo removal or after topical retinoic acid. In many patients at the acne susceptible age, some comedones refill between 30 and 50 days even after vigorous expression. The shortness of the interval reveals the high proliferative activity of keratinizing epithelia in sebaceous follicles and comedones. The turnover time of comedo epithelia or the number of horny cell layers in the comedo core produced within a given time can be ascertained by counting cell layers with fluorescein isothiocyanate and pulse labeling with 3H glycine or 3H histidine. Cell proliferation, determined by 3H thymidine in normal follicles and noninflamed comedones, is shown in a table. This and the fast movement of pulse labeled horny cell bands in comedones signify rapid follicular keratinization. Follicular regeneration determined by wound repair is also rapid. Within 3 to 8 days, puncture gaps in comedo walls disappeared. Epithelialization between a comedo and a sebaceous follicle, which marks the birth of a fistulated comedo, requires the same amount of time. Nylon threads served as paths for migrating epithelia and were completely surrounded by a sheath of keratinizing cells within 4 days. Preformed canals within the connective tissue favor the migration of epithelia and repair mechanisms. Accelerated follicular keratinization can also be produced by inflammation after potassium iodide induced follicular pustules. Severe inflammation and wound healing increase the speed of horny cell production. Fistulated comedones, mainly encountered in severe acne or acne conglobata, are the result of inflammation within follicles or comedones. Encapsulating epithelial tongues not only migrate around abscesses but link neighboring pilosebaceous units.