REPEATED EXPOSURE TO SILICONE GEL CAN INDUCE DELAYED-HYPERSENSITIVITY

The possible immunologic reactivity of silicone gel remains speculativ e and controversial. In this laboratory, a quantitative lymphocyte loc alization assay has been developed and well studied using pure lymphoc ytes collected by the technique of lymph vessel cannulation in sheep. The kinetics of antigen-specific immune responses (e.g., tuberculin re action) in this model are well described and accepted. Using the known parameters regarding the response to purified protein derivative and the classic adjuvant Freund's Complete Adjuvant, this study was design ed to identify the possible antigen-specific immunologic response, in the form of delayed-type hypersensitivity, after repeated exposure to silicone gel. Pure lymphocytes were collected by cannulating the effer ent vessel of a subcutaneous lymph node in four groups of primed sheep which, 30 days previously, had received intradermal injections of 0.9 % saline (negative controls; n = 6),Freund's Complete Adjuvant only (p ositive controls; n = 6), silicone gel (n = 7), or Freund's Complete A djuvant homogenized with silicone gel (n = 7) in an attempt to induce sensitization. Multiple (1040) intradermal skin tests were performed u sing silicone gel, purified protein derivative, and 0.9% saline. After the skin lesions had developed for 48 hours, 5 X 10(s) lymphocytes we re labeled in vitro with indium-111, returned intravenously, and allow ed to circulate for 3 hours. Sheep were euthanized, the skin lesions w ere removed, and the radioactivity was counted in a gamma spectrometer . The radioactivity in each skin lesion is considered a measure of lym phocyte accumulation. The occurrence of augmented accumulation after r eexposure to an antigen is a hallmark of delayed type hypersensitivity . The purified protein derivative and saline lesions functioned as pos itive and negative controls, with counts per minute (cpm +/- standard error) of 2404 +/- 478 (Freund's Complete Adjuvant group) and 149 +/- 21 (saline group), respectively. Significantly greater (P = 0.0021) ra dioactivity was found in the silicone gel sites (310 +/- 35) in the si licone gel-primed group and the Freund's Complete Adjuvant plus silico ne gel group (453 +/- 44; p = 0.0004) than in normal skin in each grou p. These data suggest that it be possible to induce an antigen-specifi c lymphocyte-mediated response to silicone gel.