The impact of vitamin D deficiency on immune T cells in asthmatic children: a case-control study

Abstract

Background: Vitamin D exerts profound effects on both adaptive and innate immune functions involved in the development and course of autoimmune and inflammatory diseases. As the incidence of vitamin D insufficiency is surprisingly high in the general population, experimental studies have started to investigate whether vitamin D levels (measured as serum 25 hydroxy vitamin D-25[OH]D) are correlated with immune cells and clinical parameters.

Purpose: The aim of the present research was to investigate serum vitamin D status in a case-control study in children with asthma and to study associations between vitamin D levels and certain immunological parameters.

Materials and methods: A case control study of thirty-nine children with clinically controlled asthma was enrolled to assess the relationship between serum vitamin D concentrations and disease activity. Vitamin D was assayed with a radioimmunoassay kit. We evaluated the relationship between vitamin D concentrations and forced vital capacity (FVC), forced expiratory volume in 1 second (FEV(1)), and the FEV(1)/FVC ratio. Correlations between inflammatory mediators, Th1, Th2, Th17, and regulatory T cells (Treg) and vitamin D were investigated.

Results: Only 15.38% of our asthmatic children had a sufficient serum 25(OH)D (≥30 ng/mL) whereas 80% of healthy children expressed sufficient levels. Deficient values of vitamin D (<20 ng/mL) were observed in 17 (43.59%) asthmatic patients (14.40 ± 3.30 ng/mL; P = 0.0001). Deficiency was not observed in controls. Th1/Th2 ratio was significantly correlated to 25(OH) D level (r = 0.698; P = 0.0001). A significant negative correlation was observed between serum interleukin-17 and vitamin D levels in young asthmatics (r = -0.617; P = 0.001). A significant correlation was observed between CD25(+)Foxp3(+) Treg cells and vitamin D values in asthmatics (r = 0.368; P = 0.021).

Conclusion: Even in a southern Mediterranean country, hypovitaminosis D is frequent in children with asthma. Our findings suggest that vitamin D is an important promoter of T cell regulation in vivo in young asthmatics.

Keywords: Th17; Treg cells; asthma; children; vitamin D.

Figure 1

Vitamin D concentrations of asthmatic patients. Notes: Box and whiskers plots of vitamin D concentrations of normal controls (n = 30) and asthmatic patients (n = 39). The medians are indicated by a line inside each box, the 25th and 75th percentiles are indicated by the box limits, and the lower and upper error bars represent the 10th and 90th percentiles, respectively. The mean values were compared and the P values are indicated in the figure. Moderate asthmatics expressed lower vitamin D levels than mild asthmatics did. Mann–Whitney rank sum tests assessed the difference between mild and moderate asthmatic patients.

Figure 2

Correlation between vitamin D level and serum IL-6 (A) and serum IL-17 (B) using, Pearson’s correlation coefficient. Notes: Significant positive correlation was observed for serum IL-17 level (r = 0.617; P = 0.0001). No correlation was found between serum IL-6 vitamin D levels (r = 0.068; P = 0.677). Abbreviation: IL, interleukin.

Figure 3

Intracellular Th1 and Th2 cytokines. (A–D) Box and whiskers plot of (A) percentage of interferon-gamma (IFN-γ) producing cells; (B) percentage of IL-4 producing cells; and (C) the ratio of Th1/Th2 cytokine (interferon-gamma [IFN-γ] and IL-4) determined by Fast Immune Cytokine System for normal controls (n = 30) and asthmatic patients (n = 39). The medians are indicated by a line inside each box, the 25th and 75th percentiles are indicated by the box limits, and the lower and upper error bars represent the 10th and 90th percentiles, respectively. The mean values were compared and the P values are indicated at the figure. (D) Correlation between Th1/Th2 ratio and vitamin D levels in asthmatic patients using Pearson’s correlation coefficient. Note: Mann–Whitney rank sum test assessed the differences between controls and patients. Abbreviation: IL, interleukin.

Figure 4

Intracellular Type 1 regulatory T (Tr1) cells (IL-10) and Th17 (IL-17) cytokines CD4⁺ production. Notes: Box and whiskers plot of Tr1-producing cells/Th17-producing cells ratio in asthmatic patients and healthy children. Tr1 and Th17 cytokine were determined by fast immune cytokine system from normal controls (n = 30) and asthmatic patients (n = 39). The medians are indicated by a line inside each box, the 25th and 75th percentiles are indicated by the box limits, and the lower and upper error bars represent the 10th and 90th percentiles, respectively. The mean values were compared and the P values are indicated.

Figure 5

CD25⁺Foxp3⁺ Treg in the CD4⁺ T cell compartment. Box and whiskers plot of percentage of CD25⁺Foxp3⁺ Treg in the CD4⁺ T cells (A). The medians are indicated by a line inside each box, the 25th and 75th percentiles are indicated by the box limits, and the lower and upper error bars represent the 10th and 90th percentiles, respectively. Correlation between CD25⁺Foxp3⁺ Treg cells and vitamin D levels in asthmatic patients using Pearson’s correlation coefficient (B). Note: Mann–Whitney rank sum test assessed the differences between controls and patients.