A medical follow-up of the health effects of long-term exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The human health effects of long-term exposure to low levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have not been well established. The results of a prior study showed that persons exposed to TCDD had depressed cell-mediated immunity, and 18 of 51 persons had anergy or relative anergy on skin testing. This paper presents the results of a medical follow-up on participants who were reported to be anergic or relatively anergic in the earlier study. None of the participants in the follow-up study was anergic, and only one exposed and one unexposed participant were relatively anergic. Several technical and biological possibilities for the difference in results of the two studies are presented. The possibility that recovery from the effects of TCDD exposure caused the differing results is the least plausible explanation for the changes in the skin test results.