Intestinal Helminthic Infection Increases Serum Levels of IL-2 and Decreases Serum TGF-Beta Levels in Nigerian Asthmatic Patients

Abstract

Background: Asthma is less common in countries outside the organization for economic cooperation and development (OECD). One suggested mechanism for this disparity is the early life exposure to helminthic infection in non-OECD countries due to predominant Th1 immune response, which down-regulates Th2 responses required for exacerbation of asthma. This report is the first in the literature to describe the effects of helminthic infection on immune responses in asthmatic children compared to non-asthmatic controls. Methods: We administered the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire to 1690 high school students in three rural communities in southwestern Nigeria. Based on questionnaire responses and medical examination, identified asthma cases were matched with controls. Stool samples were collected from all subjects and screened for intestinal helminthic infection. The serum of 12 asthmatics and 12 non-asthmatics (6 with intestinal helminthic infection and 6 without intestinal helminthic infection in each group) were assayed for interleukin (IL)-2, IL-4, IL-5, IL-6, IL-10, IL-12, IL-13, IL-17A, interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), granulocyte macrophage colo- ny-stimulating factor (GM-CSF), and transforming growth factor-beta (TGF-β). Results: The mean (±SD) serum levels of IL-2 significantly increased in asthma cases with intestinal helminthic infection compared with asthma cases without infection (41.5 ± 9.7 vs. 29.7 ± 10.3; p = 0.035), controls with intestinal helminthic infection compared with cases without infection (52 ± 4.7 vs. 29.7 ± 10.3; p < 0.001), and controls with intestinal helminthic infection compared to controls without infection (52 ± 4.7 vs. 34.2 ± 10.4; p = 0.003). Mean levels of TGF-β significantly increased in controls without infection compared with asthma cases with infection (1833 ± 93.1 vs. 633.3 ± 294.4; p < 0.001), controls without intestinal helminthic infection compared with asthma cases without infection (1833 ± 93.1 vs. 916.7 ± 204.1; p < 0.001), controls with intestinal helminthic infection compared to controls without infection (2366.7 ± 760.7 vs. 1833 ± 93.1; p < 0.001), and controls with intestinal helminthic infection compared with asthma cases without infection (2366.7 ± 760.7 vs.916.71 ± 204.1; p = 0.007). Conclusion: Intestinal helminthic infection independently increases IL-2 levels, while asthma decreases the level of TGF-β, which is further depressed by intestinal helminthic infection.