Impaired Ca²⁺ Regulation of CD4⁺CD25⁺ Regulatory T Cells from Pediatric Asthma

Abstract

Background: CD4⁺CD25⁺ regulatory T (T_reg) cells can control the allergic response to allergen, airway eosinophilia and airway hypersensitivity. We speculated that chronic inflammation persisting in asthma airways is dependent on abnormalities of these T_reg cells. There are differences in the pathology of asthma in adults and children, and the airways of pediatric asthma are considered to be more naive than those of adults. Therefore, we analyzed the functionality of T_reg cells in pediatric asthma and the relationship between T_reg function and asthma symptoms. Methods: The anergic state, which is one of the defining properties of T_reg, was analyzed by measuring intracellular Ca²⁺ influx following T cell receptor (TCR) stimulation. FOXP3-positive cells and FOXP3 mRNA expression were measured by flow analysis and real-time PCR with the SYBR method, respectively. Results: CD45RO⁺ cells make up approximately 99% of CD4⁺CD25^high T cells and 89% of CD4⁺CD25^low T cells in human adult blood. The proportion of CD45RO⁺ cells in CD4⁺CD25⁺ (high + low) T cells from pediatric asthma was much smaller (about 56%). Interestingly, our data indicated that CD45RO⁺ T_reg cells from pediatric asthma aberrantly increased intracellular Ca²⁺ concentrations following TCR activation compared with pediatric nonasthma controls. Conclusion: These impaired CD45RO⁺ T_reg cell functions were correlated with asthma symptoms. The correlation was observed in the group with a highly expressed atopic phenotype and longer duration of asthma. We suggest that chronic inflammation in pediatric asthma airways may be the result of impaired regulatory functions of CD45RO⁺ T_reg cells.

Immune Mechanisms of Childhood Asthma

“…In adult humans, the regulatory function of Treg cells was reduced in symptomatic hay fever subjects during the pollen season but not in asymptomatic status from the same population outside of the pollen season (Ling et al, 2004). Ca 2+ signaling is very important for lymphocyte functions and our own data have indicated that impaired Ca 2+ regulation within CD4 + CD25 + CD45RO + Treg cells correlated with child asthma symptoms (Yamamoto et al, 2011). We showed that anergy, one of the defining human Treg cell features, is dependent on intra-cellular calcium.…”

“…In contrast to effector T cells, CD4 + CD25 + Treg cells produce less IL-2, proliferate poorly, and exhibit a low level of Ca 2+ influx in response to TCR stimulation (Gavin et al, 2002;Yamamoto et al, 2011). The decline of IL-2 transcription in Treg cells is mainly attributed to the master regulator FOXP3, which is able to inhibit the function of NFAT by competing with its binding to AP-1 (Wu et al, 2006).…”

“…Murine Tregs showed a low Ca 2+ level accompanying their anergic state (Gavin et al, 2002) and our recent human Treg data imply that it the same low Ca 2+ level accompanies their anergy (Yamamoto et al, 2011). The Ca 2+ channel on the cell surface of T cells that responds to TCR stimulation is called the calcium release-activated Ca 2+ (CRAC) channel.…”

Reduced mouse allergen is associated with epigenetic changes in regulatory genes, but not mouse sensitization, in asthmatic children

“…The results may reveal that highly exposed, allergic and asthmatic children could be resistant to usual allergen-induced regulatory mechanisms due to undefined molecular impairments(Yamamoto, Negoro et al 2011), or the contribution of other genes or CpG sites within the same genes, or even other epigenetic pathways like histone acetylation or hydroxymethylation(Planell-Saguer, Lovinsky-Desir et al 2014). However, the results also do not support the paradigm that decreased FOXP3 methylation is part of the causal pathway leading to changes in mouse IgE, at least according to this timeline for a clinical allergic response.…”

The Developing Immune System and Allergy

“…These possibilities are of particular interest in light of reports that environmental exposure to airborne bacterial lipopolysaccharide in childhood may be protective against Th2-mediated sensitization to inhalant allergens. 39,278,279 It is pertinent to note that these exposures have also been observed to enhance postnatal maturation of IFN-γ-producing capacity, 280 a lack of which has been identified as a risk factor for allergy by our group and others. 271 A range of immune-associated mechanisms may contribute to these effects including modulation of TLR function initially in decidual tissue at the fetomaternal interface 272,273 and subsequently within the developing innate immune system of the offspring.…”