An Epidemiologic Investigation of Health Effects in Air Force Personnel Following Exposure to Herbicides. Volume 6.

Abstract : Of the many chemical compounds known to cause immune system dysfunction in laboratory animals, the polyhalogenated aromatic hydrocarbons have been the most extensively studied and, among these, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, or dioxin) has proven to be the most toxic. Since the early 1970s, when TCDD was shown to cause marked involution of the thymus gland in numerous experimental animals (1A), an extensive body of literature pertinent to TCDD-induced immunotoxicity has been summarized in the recent comprehensive review article by Holsapple and colleagues (5). 1 laboratory animals, TCDD has proven to have a wide range of toxic effects on all components of the immune system including the following: * Compromised cell mediated (6,7) and humoral (8-10) immune function * Impaired myelo-(1 1,12) and lymphoproliferative (11,13-15) responses * Suppressed complement activity (16,17) * Compromised host resistance to bacterial (8,11,17-19), parasitic (20), and viral (19,21) infections. In an attempt to provide data more relevant to humans, two laboratories have conducted experiments into the effects of TCDD on numerous immunologic indices in marrnoset (22-24) and rhesus monkeys (25). These studies, carried out in vitro in lymphocyte cell cultures and in vivo with single dose injections of TCDD in various concentrations, have yielded inconsistent results that in many cases do not fit a typical dose-response pattern. The relevance of these acute phase studies to the long term occupational exposure more typical in humans remains to be proven. In none of the in vivo studies have the animals shown evidence of overt illness.