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).
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.
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
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).
Baccarelli et al. 2002
does it mean? Dioxin's suppression of the immune system
persists along with the contaminant itself, decades after exposure.
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.
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.