Baccarelli, A, P Mocarelli, DG Patterson Jr., M Bonzini, AC Pesatori, N Caporaso and MT Landi. 2002. Immunologic Effects of Dioxin: New Results from Seveso and Comparison with Other Studies. Environmental Health Perspectives 110:1169-1173.

Baccarelli et al. report that the immune systems of people exposed to dioxin in the 1976 chemical plant accident in Seveso, Italy, remain suppressed now more than 20 years after the accident. The pattern of suppression would suggest increased vulnerability to infectious agents because it involved reductions in immunoglobulin G levels (IgG).

Immunoglobulins are a key part of the adaptive response of immune systems to foreign materials (antigens) that invade the body, such as infectious agents. The immunoglobulins react chemically with the antigens and diminish or destroy their virulence. IgG is the form of immunoglobulin that comprises roughly 75% of immunoglobulins in healthy individuals, and hence plays a key role in normal disease resistance.

What did they do? Baccarelli et al. measured IgG and dioxin levels in 62 individuals sampled randomly from the areas most heavily contaminated by dioxin from the accident, and another 59 subjects selected at random from the surrounding uncontaminated area. They then used statistical procedures to ascertain the relationship between IgG and dioxin exposure, while controlling for relevant confounding variables.

What did they find? IgG levels were lower in subjects with higher dioxin contamination in serum (figure below). The relationship was highly statistically significant (p < 0.0002).

from Baccarelli et al. 2002

What does it mean? Dioxin's suppression of the immune system persists along with the contaminant itself, decades after exposure.

Whether this statistical association is a result of lingering effects of the initial dioxin exposure or continuing immune system suppression by the persistent dioxin body burden cannot be determined by Baccarelli et al.'s analysis. The net result, however is the same. Dioxin-exposed people are less likely to resist infectious agents with the same efficiency as unexposed people.

As Baccarelli et al. discuss, these results are largely consistent with a wide variety of other reports on immune system impairment by dioxin, both in humans and in laboratory animals.