Health Complaints
Allergies - can they begin in the womb? |
Allergies to common foods and substances are becoming ever more widespread in the modern age. This may be associated with greater exposure and challenges to the immune system, or with a generally poor state of nutrition from the modern diet. These allergies are presenting themselves in forms that vary from the atopic triangle (asthma. eczema, and hayfever) right through to the immediately life threatening anaplylactic shock type of reaction to allergens.
Many of these allergies are being observed in children even as young as a few days old, which has lead to the theory that allergies may begin to develop in utero (in the womb). According to Dr Gill Dealtry of the University of Essex there is evidence to show that a foetus is exposed to a Th2 type environment whilst in the womb (Dealtry et al 1998:283). The cytokines secreted by T cells in the Th2 subset induce B cells to express immunoglobulin E (IgE) - which is involved in the allergic response. It is believed that if the foetus is exposed to a Th2 environment for long enough, it will cause a biasness towards a Th2 state in the foetal immune system.
This has been further supported by studies of placental tissue during the first trimester of pregnancy. Such studies have indicated the presence of Th2 cytokines, with no evidence of Th1 cytokines being present (Vince & Johnson 1996:101). There is also evidence of in utero sensitisation taken from the study of cord blood mononuclear cells. These cells were found to be able to proliferate when exposed to common allergens immediately after birth (Prescott et al 1998:4730). This ability to immediately profliferate strongly suggests that sensitisation occurred during gestation (1998:4730).
In light of these findings, the medical profession has sugested, where feasibly possible, the avoidance of many common allergens. These include certain household products and cleaning materials, and foods such as peanuts and shellfish. These should be avoided even if the mother has no allergic symptoms to any of these substances. There can still be a response to these substances by the mothers immune system, but on a small enough scale to be asymptomatic. However, if immune complexes formed during this exposure cross the placenta, the above type of sensitisation may well occur.
References
Dealtry G, Clark D, Shark A, et al. Expression and localization of the Th2 cytokine IL-13 and its receptor in the placenta during human pregnancy. Am J Reprod Immunol. 1998;40:283-290.
Prescott S, Macaubas C, Holt BJ, et al. Transplacental priming of the human immune system to environmental allergens: universal skewing of initial T cell responses towards the Th2 cytokine profile. J Immunol. 1998;60:4730-4737.
Vince G, Johnson P. Is there a Th2 bias in human pregnancy? J Reprod Immunol. 1996;32:101-104.