Endotoxins, part of the outer membrane of Gram negative bacteria, are a potent inducer of neutrophilic airway inflammation. A large number of studies in occupational epidemiology has shown that exposure to endotoxins increases the likelihood of organic dust toxic syndrome, chronic bronchitis, and asthma-like syndrome. In contrast, it has been shown that exposure to endotoxins in the occupational and environmental setting protects from respiratory allergies and sensitisation to allergens.

With respect to asthma, the evidence is conflicting at first glance. While some studies indicated an increased risk of asthma after endotoxin exposure, others have shown that endotoxin exposure protects from asthma. However, these differences can be explained when different asthma phenotypes are taken into account. The risk of atopic asthma, mainly dominated by eosinophilic response, is decreased in those exposed to endotoxins. In contrast, the risk of non-atopic asthma, characterised by neutrophilic response, is enhanced in subjects with higher endotoxin exposure. These data are in accordance with the so-called hygiene hypothesis and have been supported by animal studies and at the cellular level.

At the workplace, measures should therefore be taken in order to reduce endotoxin exposure. The effectiveness of such measures with respect to the incidence of diseases associated with a chronic neutrophilic inflammation in the airways should be assessed in intervention studies. At the same time we need to learn whether the evidence from epidemiological studies in farming environments might help us to obtain effective intervention strategies against allergies.

WHAT ARE ENDOTOXINS?

In contrast to Gram positive bacteria, Gram negative bacteria are surrounded by an inner and an outer membrane.¹ Endotoxins are parts of the outer membrane. Their purified derivatives are called lipopolysaccharides (LPS).²

Endotoxins and LPS are present in the oral and nasal cavities of humans and animals. They can also be found ubiquitously in occupational and environmental …