Longitudinal relationship of early life immunomodulatory T cell phenotype and function to development of allergic sensitization in an urban cohort

Abstract

Background: Immunomodulatory T cells are thought to influence development of allergy and asthma, but early life longitudinal data on their phenotype and function are lacking.

Objectives: As part of the Urban Environment and Childhood Asthma (URECA) study, we investigated the development of immunomodulatory T cell phenotype and function, and characterized their relation to allergic disease progression from birth through to 2 years of age.

Methods: Immunomodulatory T cell phenotype and function in cord blood mononuclear cells (CBMC) and peripheral blood mononuclear cells (PBMC) at 1 and 2 years of age were characterized by analysing CD25(bright) and FoxP3(+) expression, proliferative responses and cytokine production. The relation of immunomodulatory T cell characteristics to allergic sensitization and disease at 1- and 2-years of age was investigated.

Results: The proportion of CD4(+)CD25(bright) and CD4(+)CD25(+)FoxP3(+)T cells (n = 114, 83, 82 at birth, 1- and 2-years respectively) increased significantly, whereas there were no significant changes in the suppressive function of CD25(+)T cells (n = 78, 71, 81 at birth, 1- and 2-years respectively). Birth immunomodulatory T cell characteristics were not related to subsequent allergic sensitization or disease. However, increases in the numbers of CD4(+)CD25(bright) cells and their ability to suppress lymphoproliferative responses at 1 year of age were associated with reduced allergic sensitization at 1 (P = 0.03) and 2 (P = 0.02) years of age. Production of the anti-inflammatory cytokine IL-10 by CD25(+)T cells appeared to mediate this protective suppressive function. In contrast, by 2 years of age, we observed the emergence of a positive association of CD4(+)CD25(+) FoxP3(+) T cell numbers with allergic sensitization (P = 0.05) and eczema (P = 0.02).

Conclusions and clinical relevance: These findings suggest that the relationship between immunomodulatory T cell subsets, allergic sensitization and eczema is developmentally regulated. In the first year of life, CD4(+)CD25(+) IL-10 producing T cells are associated with a reduced incidence of allergic sensitization. Once allergic sensitization or eczema is established, CD4(+)CD25(+)FoxP3(+)T-reg cells expand to potentially counteract the allergic inflammatory response. Understanding the relationship between development of immunoregulatory T cells and early onset atopy could lead to new preventive strategies for allergic diseases.

Figure 1. Immunomodulatory T-cells increase in number and functionality over time

SI of CD25⁺ cells and proportions of CD4⁺CD25^bright and CD4⁺CD25⁺FoxP3⁺ cells were assessed over time. Wilcoxon rank sum testing evaluated changes in cellular characteristics between time points. Bars represent median values. P-values indicated on graph for comparisons of cellular characteristics between time points.

Figure 2. Immunomodulatory T-cell numbers and suppressive function, in first year of life are negatively associated with allergic sensitization

Spearman correlations evaluated the relation of SI, and proportions of CD4⁺CD25^bright and CD4⁺CD25⁺FoxP3⁺ cells at age-1 to clinical outcomes at 1 (A) and 2 (B) years. Correlation coefficients (circles) and direction of associations are indicated. Significant associations (p<0.05) are highlighted by closed circles. P-values for each association listed on right of each panel.

Figure 3. Suppressive function of CD25⁺ T-cells at age-1 are reduced in allergic individuals at 1- and 2-years

Wilcoxon rank sum test compared suppressive index at age-1 in those that had a positive or negative RAST test at 1-year (A) and 2-years (B) and a positive RAST test to Egg specific IgE at 1-year (C) and 2-years (D).

Figure 4. Immunomodulatory T-cell numbers and suppressive function, at age2 years are not negatively associated with allergic sensitization at age 2 years

Spearman correlations evaluated the relationship between SI, proportions of CD4⁺CD25^bright, CD4⁺CD25⁺FoxP3⁺ at 2-years, to clinical outcomes at 2-years. Correlation coefficients (circles) and direction of associations are indicated. Significant associations (p<0.05) are highlighted by closed circles. P-values for each association listed on right of each panel.

Figure 5. Allergic sensitization in the first year of life influences CD4⁺CD25⁺FoxP3⁺ T-cell numbers by age-2

Wilcoxon rank sum test compared proportions of CD4⁺CD25⁺FoxP3⁺ cells at age-2 in individuals that had a positive or negative RAST test at 1-year (A). Spearman correlations evaluated relationship between proportions of CD4⁺CD25⁺FoxP3⁺ cells at age-2 with total IgE levels at 1-year (B). Correlation coefficient and p-value (parenthesis) indicated on graph.

Figure 6. IL-10 production by CD25⁺ T-cells mediates suppressive function and protects against allergic sensitization at age-1

Wilcoxon rank sum test compared PHA-induced IL-10 production by MNC at age-1 in individuals that had a positive or negative RAST test at 1-year (A). Spearman correlation evaluated associations between IL-10 and proportions of CD4⁺CD25^bright cells at 1-year Correlation coefficient and p-value (parenthesis) indicated on graph (B). Wilcoxon rank sum test compared PHA-induced IL-10 production by total MNC and CD25-depleted MNC at 1-year (C). MNC proliferation in response to PHA was assessed at 2-years in the presence or absence of rIL-10 (D).