Inflammatory mediators and modulators released in organ culture from rabbit skin lesions produced in vivo by sulfur mustard. I. Quantitative histopathology; PMN, basophil, and mononuclear cell survival; and unbound (serum) protein content

When applied topically to the skin of rabbits in vivo, sulfur mustard (SM), the vesicant used in World War I, produced a slowly developing inflammatory response, which peaked in size at 1 and 2 days, ulcerated within 3 days, and reepithelialized by 10 days. Histopathologically, basophils and polymorphonuclear leukocytes (PMNs) were common in both early and late lesions, and the crust over the ulcers was composed of dead epidermal cells, fibrin, and large numbers of PMNs. Healing occurred under the crust by migration of epidermal cells from the margins of the lesions and from the hair follicles. In organ culture, the lesions explants survived well, and reepithelialization even took place. Their excellent survival enabled us to compare the life spans of the infiltrating leukocytes within an inflammatory site. PMNs within the explants began disappearing during the first day of culture, and almost all had disappeared by 3 days. In contrast, over half of the basophils and the mononuclear cells within the explants were still present after 3 days of culture. The 1-, 2-, 3-, 6-, and 10-day (1.0-sq cm) SM lesion biopsies showed a 30-45% increase in weight (when compared with normal skin), presumably due to the extravasation of serum proteins and the fluids retained by them. When the biopsies were organ-cultured for 3 days, the 1-, 2-, and 3-day lesions lost weight, and the 6- and 10-day lesions (and normal skin) gained weight. These weight differences were not due to the amount of unbound protein extractable into the culture fluids, because both the early lesions and the late lesions contained about the same amount of unbound protein. The most likely explanation for these weight differences is that the newly formed ground substances had changed from the sol state of acute inflammation (in which it was extractable) back to its normal gel state (in which it was not extractable). The unbound protein extractable into the culture fluids was mostly of serum origin. This protein averaged 1.9 mg for 1.0 sq cm normal skin explants (with a mean weight of 215 mg), and 6.4 mg for 1-day SM lesions (with a mean weight of 313 mg). Because rabbit serum contains about 60 mg protein/ml, these figures indicate that normal skin contained about 15% (unbound) serum by weight. The presence of such large amounts of serum in normal and inflamed skin suggests that serum could be a major source of mediators and modulators of the inflammatory response.