Allergy, Parasites, and the Hygiene Hypothesis

Abstract

The increase of allergic diseases in the industrialized world has often been explained by a decline in infections during childhood. The immunological explanation has been put into the context of the functional T cell subsets known as T helper 1 (TH1) and T helper 2 (TH2) that display polarized cytokine profiles. It has been argued that bacterial and viral infections during early life direct the maturing immune system toward TH1, which counterbalance proallergic responses of TH2 cells. Thus, a reduction in the overall microbial burden will result in weak TH1 imprinting and unrestrained TH2 responses that allow an increase in allergy. This notion is contradicted by observations that the prevalence of TH1-autoimmune diseases is also increasing and that TH2-skewed parasitic worm (helminth) infections are not associated with allergy. More recently, elevations of anti-inflammatory cytokines, such as interleukin-10, that occur during long-term helminth infections have been shown to be inversely correlated with allergy. The induction of a robust anti-inflammatory regulatory network by persistent immune challenge offers a unifying explanation for the observed inverse association of many infections with allergic disorders.

Endotoxin in inner-city homes: Associations with wheeze and eczema in early childhood

“…The prevalence of asthma generally is greater among industrialized countries, where living conditions appear to be cleaner and fewer bacterial infections seem to occur, than among developing nations (10,11). However, it is unclear where inner-city homes in the U.S., generally afflicted by a disproportionately high prevalence of asthma, fall in the spectrum of environmental endotoxin exposure (4,12).…”

Immunoglobulin gene analysis as a tool for investigating human immune responses

“…The major differences between IgA1 and IgA2 lies in the presence of the drastically extended hinge region of IgA1, thought to improve antigen recognition by increasing affinity with antigen epitopes that are spatially distant, but making it vulnerable to proteases 37, 38, 39. The IgE antibody has received an increasing amount of attention because of its role in hypersensivity responses and allergy in the developed world, although initially thought to have evolved to target parasites (eg, helminths and parasitic arthropods) that are too large to be phagocytosed 40, 41, 42…”

Expressing urine from a gel disposable diaper for biomonitoring using phthalates as an example

“…This states, in its purest form, that exposure of the neonatal immune system to certain infectious agents and/or their immunostimulatory components (such as lipopolysaccharide of Gram-negative bacteria) is an important component of immune maturation and may be necessary for appropriate Th1 development (Strachan, 1989(Strachan, , 1999Cremonini & Gasbarrini, 2003). However, other researchers dispute the "hygiene hypothesis" in favour of a tenet that it is the development of robust anti-inflammatory responses early in life that helps protect against or minimize allergic disorders (Yazdanbakhsh et al, 2002).…”