The adjuvant effect of silicone gel and silicone elastomer particles in rats

This study examines the adjuvant properties of silicone oil, silicone gel and silicone elastomer using a foreign antigen, bovine serum albumin (BSA). Seventy male Harlan Sprague-Dawley rats, approximately 250 grams each, were divided into 7 groups: A- incomplete Freund's adjuvant (IFA) with BSA; B- silicone oil with BSA; C- IFA/silicone oil with BSA; D- 50% silicone gel/50% silicone oil with BSA; E- silicone oil/1000 microns elastomer particles with BSA; F- silicone oil/500 microns elastomer particles with BSA; G- saline with BSA. Rats were implanted intramuscularly with mixtures or emulsions of the above described treatment materials. Cardiac punctures were performed on days 0, 14, 28, 42, and 55. Serum IgG antibody response to BSA was determined by enzyme-linked immunosorbent assay (ELISA). Rats were sacrificed on day 55 and sections of the injection sites were collected and stained for histopathologic evaluation. The results demonstrated that silicone gel functions as a potent immunologic adjuvant as measured by a heightened IgG antibody response to BSA. In contrast silicone elastomer particles have no apparent adjuvant effect as determined by the low anti-BSA antibody levels in these treatment groups throughout the course of the study. Histologically, silicone gel and silicone elastomer elicit a moderate to severe "foreign body" granulomatous inflammatory response at the injection site. Silicone oil elicits mild or no local inflammatory response.