Expression and clinical significance of serum interleukin-21 in patients with different types of tuberculosis

Objective To investigate the expression level of interleukin 21 (IL-21) and its correlation with tuberculosis antibody in patients with different clinical types of tuberculosis. Methods From October 2014 to June 2018, a total of 180 patients with primary tuberculosis in The Sixth Affiliated Hospital of Kunming Medical University were divided into two groups according to the lesion locations: pulmonary tuberculosis group (n = 99, including 37 cases with tuberculous pleurisy) and extrapulmonary tuberculosis group (n = 81); while 140 healthy volunteers were selected as control group. The levels of serum IL-21 and anti-Mycobacterium tuberculosis antibody in the patients with tuberculosis before and after anti-Mycobacterium tuberculosis treatment were detected by Enzyme linked immunosorbent assay (ELISA). IL-21 levels in pleural effusions were detected in patients with tuberculosis pleurisy before treatment. The correlation between serum IL-21 level and anti-Mycobacterium tuberculosis expression was analyzed. Results Before anti-Mycobacterium tuberculosis treatment, the serum IL-21 levels in both pulmonary tuberculosis patients [43.16 (72.98) pg/ml] and extrapulmonary tuberculosis patients [38.68 (58.17) pg/ml] were lower than those of healthy controls [59.49 (42.41) pg/ml], with significant differences (Z =-2.788, P = 0.005; Z =-2.788, P = 0.005); but there was no significant difference between pulmonary tuberculosis group and extrapulmonary tuberculosis group (Z = -0.052, P = 0.961). After intensive anti-Mycobacterium tuberculosis treatment, the serum IL-21 levels of both pulmonary tuberculosis and extrapulmonary tuberculosis patients were significantly increased [60.21 (57.58) pg/ml vs. 43.16 (72.98) pg/ml; Z =-2.681, P = 0.007; 66.16 (42.21) pg/ml vs. 38.68 (58.17) pg/ml; Z =-2.422, P = 0.015]. The average level of IL-21 in pleural effusion of patients with tuberculous pleurisy in pulmonary tuberculosis group was significantly higher than their serum IL-21 level before anti-Mycobacterium tuberculosis [121.36 (133.67) pg/ml vs. 49.09 (80.67) pg/ml; Z =-3.477, P = 0.001]. Conclusions The level of serum IL-21 in patients with active tuberculosis decreased and increased after anti-Mycobacterium tuberculosis, suggesting that the level of IL-21 may be used as an index for observing the effect or clinical outcome of patients with tuberculosis. Key words: Tuberculosis; Interleukin-21; Cytokines; Mycobacterium tuberculosis; Humoral immunity