Environmental exposure to endotoxin and its relation to asthma in school-age children
Authors: Leticia Grize
Albrecht Bufe
Allergy and Endotoxin Study Team
Marco Waser
Roger P Lauener
Josef Riedler
Rudolf Schierl
Waltraud Eder
Dennis Nowak
Soyoun Maisch
Udo Herz
David Carr
Erika von Mutius
Harald Renz
Charlotte Braun-Fahrländer
Florian Gerlach
Journal: New England Journal of Medicine (2002)
Discipline: CLINICAL MEDICINE
Keywords: innate immune system; allergens; atopic sensitization; endotoxin levels; hay fever
Affiliations: Institute of Social and Preventive Medicine, Basel, Switzerland. 

Abstract:  Background: In early life, the innate immune system can recognize both viable and nonviable parts of microorganisms. Immune activation may direct the immune response, thus conferring tolerance to allergens such as animal dander or tree and grass pollen. Methods: Parents of children who were 6 to 13 years of age and were living in rural areas of Germany, Austria, or Switzerland where there were both farming and nonfarming households completed a standardized questionnaire on asthma and hay fever. Blood samples were obtained from the children and tested for atopic sensitization; peripheral-blood leukocytes were also harvested from the samples for testing. The levels of endotoxin in the bedding used by these children were examined in relation to clinical findings and to the cytokine-production profiles of peripheral-blood leukocytes that had been stimulated with lipopolysaccharide and staphylococcal enterotoxin B. Complete data were available for 812 children. Results: Endotoxin levels in samples of dust from the child's mattress were inversely related to the occurrence of hay fever, atopic asthma, and atopic sensitization. Nonatopic wheeze was not significantly associated with the endotoxin level. Cytokine production by leukocytes (production of tumor necrosis factor alpha, interferon-gamma, interleukin-10, and interleukin-12) was inversely related to the endotoxin level in the bedding, indicating a marked down-regulation of immune responses in exposed children. Conclusions: A subject's environmental exposure to endotoxin may have a crucial role in the development of tolerance to ubiquitous allergens found in natural environments. 

Retracted: No

PubPeer comments:
 FIG1A shows sharp axis and tick marks but data circles are unsharp (scanned, painted, mounted?) The plot shows only smoothed data without confidence limits and some unusual span value [[1] ] The loess fit contradicts table 1 results where something in the range of farming 29,897 4.1 and non-farming 14,456 10.5 should have been observed. ![file] To be continued. , 
 FIG 2C is not showing the full range of endotoxin load on the horizontal axis. According to table 1 the 5th to 95th percentile range is between 2,915 and 157,208. The vertical axis is also hard to understand. To show data on a logscale, at least one logscale unit needs to be displayed. The authors interprete the plot as a significant  inverse relation ... between the level of endotoxin exposure and the capacity of peripheral-blood leukocytes to produce inflammatory and regulatory cytokines after stimulation with lipopolysaccharide . I see only some 10%-15% reduction of IL 12 production in the farming children who are mostly on the right side of the plot. Any negative association therefore may not be related to endotoxin at all. According to the [accompanying editorial](http: )  at low levels, lipopolysaccharide is a potent inducer of interleukin-12 while the plot shows a negative association. , 
 Like FIG1A the loess fit in FIG3B contradicts table 1 results for nonatopic wheeze where more than half of the sample has higher values than plotted here. , 
 Of course there might be some highly skewed distributions in the two subgroups farm non-farm that could explain the Loess smoother shown for the total sample in FIG 1--3 but then it would be irresponsible to hide the subgroup results. At least the risk estimates between subgroup and total sample do not differ so much according to table 2. , 
 FIG 1A-C do not show the two observations at 100 units m^2 that are depicted in FIG 2A-D. Adding 10% FCS to primary cell cultures and measuring afterwards cell-free supernatant for cytokines (would need also some FCS free controls)[https: www.ncbi.nlm.nih.gov pubmed 7578990]. The authors do not cite here their own [earlier studies] raising the question if this a circular analysis of already published data. , 
 This is a highly selected sample - selection criterium is low asthma allergy prevalence and country side. So any association may have been introduced just by unequal selection of key variables. And indeed, there are 493 lower exposed non-farm households and 319 higher exposed farm households that are analyzed together in table 2. Why are results from farm households omitted here? Why are different confounder included in comparable models? It makes no sense to include study area in the non-farm model. It seem also necessary to show that there is no residual confounding in the combined model. Endotoxin has been included in quartiles although [there are numerous reasons] why this can be leading to wrong results. ,