Impaired Toll-like receptor 2 signalling in monocytes from 5-year-old allergic children

The relative composition of the two major monocytic subsets CD14(+)CD16(-) and CD14(+)CD16(+) is altered in some allergic diseases. These two subsets display different patterns of Toll-like receptor levels, which could have implications for activation of innate immunity leading to reduced immunoglobulin E-specific adaptive immune responses. This study aimed to investigate if allergic status at the age of 5 years is linked to differences in monocytic subset composition and their Toll-like receptor levels, and further, to determine if Toll-like receptor regulation and cytokine production upon microbial stimuli is influenced by the allergic phenotype. Peripheral blood mononuclear cells from 5-year-old allergic and non-allergic children were stimulated in vitro with lipopolysaccharide and peptidoglycan. Cells were analysed with flow cytometry for expression of CD14, Toll-like receptors 2 and 4 and p38-mitogen-activated protein kinase (MAPK). The release of cytokines and chemokines [tumour necrosis factor, interleukin (IL)-1 beta, IL-6, IL-8, IL-10, IL-12p70] into culture supernatants was measured with cytometric bead array. For unstimulated cells there were no differences in frequency of the monocytic subsets or their Toll-like receptor levels between allergic and non-allergic children. However, monocytes from allergic children had a significantly lower up-regulation of Toll-like receptor 2 upon peptidoglycan stimulation. Further, monocytes from allergic children had a higher spontaneous production of IL-6, but there were no differences between the two groups regarding p38-MAPK activity or cytokine and chemokine production upon stimulation. The allergic subjects in this study have a monocytic population that seems to display a hyporesponsive state as implicated by impaired regulation of Toll-like receptor 2 upon peptidoglycan stimulation.

Maternal allergy influences p38-mitogen-activated protein kinase activity upon microbial challenge in CD14+ monocytes from 2-year-old children

BACKGROUND

The development of allergic diseases is dependent on genetic and environmental factors. It has been shown previously that cord blood mononuclear cells (CBMCs) from infants with parental allergy have altered cytokine profiles upon bacterial encounter; it might be possible that such impairment persists during the early years of childhood.

OBJECTIVE

The aim of this study was to investigate anti-microbial responses with regard to p38-mitogen-activated protein kinase (MAPK) activity in CD14(+) monocytes and IL-6 release from mononuclear cells in the same group of children at birth and at 2 years of age. Methods Paired samples of CBMCs and peripheral blood mononuclear cells (PBMCs) were stimulated with either lipopolysaccharide (LPS) or peptidoglycan in vitro. CD14(+) monocytes were analysed for p38-MAPK activity by flow cytometry, and soluble IL-6 receptor, soluble glycoprotein130 and IL-6 release from PBMC cultures were quantified by ELISA.

RESULTS

CBMCs from newborns with allergic mothers tended to have a lower IL-6 response following an LPS (P=0.09) challenge compared with the group without maternal allergy while p38-MAPK activation levels did not differ between the groups. PBMCs from 2-year-olds with allergic mothers released significantly less (P<0.05) IL-6 upon peptidoglycan stimuli compared with age-matched infants with non-allergic mothers. Infants with allergic mothers displayed markedly reduced CD14(+) monocyte p38-MAPK phosphorylation after LPS (P<0.05) and peptidoglycan (P<0.01) challenge. This altered anti-microbial response was attributed to maternal allergy rather than to being IgE-sensitized at 2 years of age.

CONCLUSION

Monocytes from children with allergic mothers are less responsive to bacterial challenge than monocytes from children with non-allergic mothers, and this impairment persists during the first 2 years of infancy.