Bedding dust is a mixture of many components, of which the house dust mite (HDM) allergen, Der p 1, is the most allergenic. There has been little work to investigate the effect of other bedding dust components on HDM sensitisation. The objective of the study was to determine the effect of endotoxin in bedding dust on the allergic response in HDM-sensitised individuals. Twenty-nine house dust mite-sensitised adults were skin prick and allergen patch tested against a sterile solution of their own bedding dust and against a solution containing the same concentration of Der p 1 as the bedding solution for comparison. There was no significant difference in wheal size between the diluted house dust mite solution and the bedding dust in spite of their high levels of endotoxin. Symptomatic subjects had larger, but not statistically significant, responses to commercial house dust mite solution than asymptomatic subjects. Allergen patch test responses were negative in 22/29 of subjects using either bedding dust solutions or comparable diluted house dust mite solutions. An individual's own bedding dust does not appear to contain factors that enhance skin prick test or atopy patch test responses to house dust mites. 1. Introduction Sensitivity to house dust was confirmed in the 1920s by studies showing positive skin prick tests to house dust in many asthmatic individuals [1]. Such studies sparked scientific interest into what specific component of house dust was responsible for the sensitisation but it was not until the 1960s that Voorhorst and colleagues discovered Dermatophagoides pteronyssinus to be the major producer of house dust allergen [2, 3]. Since these early studies into house dust mite (HDM) sensitivity, there has been much research into the relationship between HDM sensitivity and atopic diseases which have concluded that initial HDM sensitisation and subsequent exposure are strongly linked to asthma, atopic dermatitis, and allergic rhinitis. In particular, the evidence for asthma is strong enough that a causal relationship is widely accepted [1]. Interestingly, despite HDM exposure being accepted as an exacerbating factor in asthma, studies have failed to find a relationship between levels of HDM allergen in the home and asthma symptom severity. Instead, these studies have found asthma severity to better correlate with levels of bacterial endotoxin in house dust [4–6]. Endotoxins are lipopolysaccharide molecules that are found on the outer cell membrane of Gram-negative bacteria. They are known to be potent inducers of inflammation and are present in
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