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

Haïfa Maalmi,^1,2 Anissa Berraïes,^1,2,3 Eya Tangour,^1,2,3 Jamel Ammar,^1,2,3 Hanadi Abid,^1,2,3 Kamel Hamzaoui,^1,2 Agnes Hamzaoui<sup>1,2,3

1</sup>Department of Basic Sciences, Medicine School of Tunis, University Tunis El Manar, Tunis; ²Unit Research, Homeostasis and Cell Dysfunction, Ariana; ³Department of Pneumopediatry, A Mami Hospital, Ariana, Tunisia

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 (FEV₁), and the FEV₁/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: vitamin D, Th17, Treg cells, asthma, children