Antigen-specific IgG1-mediated epidermal cell injury: A component of contact hypersensitivity reactions in guinea pigs, measurable in vitro in full-thickness skin explants

Guinea pigs were sensitized by the topical application of either dinitrochlorobenzene (DNCB) or oxazolone on days 1, 2, 3, and 10. Seventeen days after the first treatment with the sensitizer, full-thickness 1.0-cm² explants of untreated areas of skin were topically exposed in vitro to these contactants. Compared to the response of skin from control guinea pigs, skin from specifically sensitized animals showed a doserelated increase in the number of epidermal cells containing vacuoles. A specific increase in epidermal microblistering paralleled the increase in epidermal vacuolization. In addition, skin explants from sensitized animals (exposed to the contactant) showed a specific decrease in the incorporation of [¹⁴C]leucine. Full-thickness skin explants from unsensitized guinea pigs were sensitized in vitro by the intradermal injection of serum IgG1 fraction from oxazolone-sensitized guinea pigs. In such passively sensitized explants, the specific contactant produced an increase in the number of epidermal vacuoles, an increase in the amount of microblistering, and a decrease in the number of mast cells detectable by Giemsa staining. To elicit this specific response, the concentration of the specific contactant had to be mildly injurious, as well as antigenic. This requirement for nonspecific injury could be met by topically exposing skin explants to a nonspecific irritant followed by a sub-threshold concentration of the specific contactant. In contrast to vacuole formation and blistering, contactant-specific degranulation of mast cells (measured by the decrease in their number) did not require irritant levels of the contactant. These studies show that several components of contact sensitivity reactions can be reproduced in vitro by the passive transfer of sera containing antigen-specific immunoglobulins. Banks of such sera might, therefore, be useful in identifying (in human populations) many pre-existing sensitivities to chemical compounds.