One of the allergens (Der p1) in the droppings from the mite can gain entry into the womb following inhalation by the mother. Once absorbed into her bloodstream, Der p1 crosses the placenta wall to become part of the ‘soup’ that is known as the amniotic fluid. Prior to birth the unborn child can drink up to 0.7 litres of this fluid per day and absorb 10% of its content.1
A recent study has demonstrated that up to 20% of newly born infants react to the mite’s invasive allergen with an immunological marker at birth. Scientists are trying to establish whether this phenomenon is a primary cause of an allergic reaction, or a natural reaction to the allergen’s presence. 2 Universally babies are born with an immature immune system that is skewed towards the allergic response (Th2). This response is the hallmark of a successful pregnancy and a protective reaction against parasites. Following birth most infants switch away from the allergy mechanism to an immune response that is more appropriate and against bacterial infection (Th1). Some children appear slow to switch. These children may get “locked into” allergy by re-exposure to the droppings during infancy. 3,4 This exposure may retard, or even prevent progress towards the safer and preferred bacterial pathway(Th1). It is important to identify and protect this vulnerable group from the allergic pathway. Doctors are working on the development of a simple test that may identify vulnerable infants at birth. After identification it is up to the parents or guardians to help their children to avoid the known provoking factors of allergy. 5,6 The house dust mite’s allergen Der p1 can actually cause asthma in the first place.7 References: 1. Holloway J A, Warner J O, Vance G H S, Diaper N D, Warner J A, Jones C A. ‘Detection of House Dust Mite allergen in amniotic fluid and umbilical-cord blood’; The Lancet, 12/02/2000, Issue 9245, 1900-1902.
2. Devereux G, Hall A M, Barker R N, ‘Measurement of T-helper cytokines secreted by cord blood mononuclear cells in response to allergens’; Journal of Immunological Methods, 2000, 234, , 13-22
3. Holt P.G.et al, ‘Transplacental priming of the human immune system to environmental allergens: Universal skewing of initial T cell responses toward the Th2 Cytokine Profile’, J.Immunol., 1998, 160: 4730-4737
4. Young RP, Hart BJ, Merrett TG, Read AF, Hopkin JM, ‘House dust mite sensitivity: interaction of genetics and allergen dosage’, Clin.& Exp Allergy,1992, 22: 205-211
5. Nelson Harold S. Editorial ‘The importance of allergens in the development of asthma and the persistence of symptoms’ J.All & Clin.Immun. Jun 2000,105,No.6b, Pt II
6. Kalliomäki M, Salminen S, Arvilommi H, Kero P, Koskinen P, Isolauri E. ‘Probiotics in primary prevention of atopic disease: a randomised placebo-controlled trial’, The Lancet, 07/04/2001:1076-1079.
7. National Asthma Campaign, Asthma News, Issue 60, Spring 2000,
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