High indoor microbial levels are associated with reduced Th1 cytokine secretion capacity in infancy.
BACKGROUND
Exposure to microbes and their components may affect the maturation of the immune system. We examined the association of house dust microbial content with cytokine-producing capacity at birth and at the age of 1 year.


METHODS
Production of TNF-α, IFN-γ, IL-5, IL-8 and IL-10 at birth (n = 228) and at the age of 1 year (n = 200) following 24- and 48-hour whole-blood stimulation with staphylococcal enterotoxin B (SEB), lipopolysaccharide and the combination of phorbol ester and ionomycin was measured. Concentrations of ergosterol (marker for fungal biomass), muramic acid (marker for Gram-positive bacteria) and 3-hydroxy fatty acids with a carbon chain length from 10 to 14 (marker for Gram-negative bacteria) in living room floor dust were analyzed using gas chromatography-tandem mass spectrometry. Five single microbial species or groups were determined using a quantitative polymerase chain reaction method.


RESULTS
A high total level of the studied Gram-positive bacteria in general or Mycobacterium spp. in house dust was associated with decreased SEB-stimulated IFN-γ production, especially at the age of 1 year. The total level of indoor fungi analyzed (Penicillium spp., Aspergillus spp. and Paecilomyces variotii group, Trichoderma viride/atroviride/koningii,Wallemia sebi) was also inversely associated with IFN-γ production at the age of 1 year, but this association did not remain significant after adjustment for potential confounders. A few associations were found between microbial exposures and other measured cytokines.


CONCLUSIONS
High indoor microbial exposures may affect immune development in early life by reducing T helper type 1 cytokine secretion capacity. The observed hyporesponsiveness may reflect the adaptation of the immune system to environmental antigens. In future, more attention should be paid especially to the immunomodulatory role of exposures to Gram-positive bacteria.
Department of Environmental Health, National Institute for Health and Welfare, Kuopio, Finland.
Mikko Harri Juhani
MH
Lappalainen
Anne
A
Hyvärinen
Maija-Riitta
MR
Hirvonen
Helena
H
Rintala
Jarkko
J
Roivainen
Harald
H
Renz
Petra Ina
PI
Pfefferle
Aino
A
Nevalainen
Marjut
M
Roponen
Juha
J
Pekkanen
D000222:Adaptation, Physiological; D000391:Air Microbiology; D058491:Bacterial Load; D015331:Cohort Studies; D015169:Colony Count, Microbial; D016207:Cytokines / Q000096:biosynthesis*; D004391:Dust / Q000276:immunology; D004781:Environmental Exposure; D005260:Female; D005387:Finland; D005658:Fungi / Q000276:immunology / Q000302:isolation & purification; D006094:Gram-Positive Bacteria / Q000276:immunology / Q000302:isolation & purification; D006801:Humans; D007107:Immune System / Q000254:growth & development; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D011247:Pregnancy; D011446:Prospective Studies; D018417:Th1 Cells / Q000276:immunology*
D016207:Cytokines; D004391:Dust