Relationship between Circulating Levels of IFN‐γ, IL‐10, CXCL9 and CCL2 in Pulmonary and Extrapulmonary Tuberculosis is Dependent on Disease Severity

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Abstract
Protection against Mycobacterium tuberculosis infection is dependent on T cell and macrophage activation regulated by cytokines. Cytokines and chemokines produced at disease sites may be released into circulation. Data available on circulating cytokines in tuberculosis (TB) is mostly on pulmonary TB (PTB) with limited information on extrapulmonary disease (EPul‐TB). We measured interferon‐gamma (IFN‐γ), interkeukin‐10 (IL‐10), CXCL9 and CCL2 in sera of patients (n = 80) including; PTB (n = 42), EPul‐TB (n = 38) and BCG vaccinated healthy endemic controls (EC, n = 42). EPul‐TB patients comprised those with less severe (LNTB) or severe (SevTB) disease. Serum IFN‐γ, IL‐10 and CXCL9 levels were significantly greater while CCL2 was reduced in TB patients as compared with EC. IFN‐γ was significantly greater in PTB as compared with LNTB (P = 0.002) and SevTB (P = 0.029). CXCL9 was greater in PTB as compared with LNTB (P = 0.009). In contrast, CCL2 levels were reduced in PTB as compared with LNTB (P = 0.021) and SevTB (P = 0.024). A Spearman’s rank correlation analysis determined a positive association between IFN‐γ and IL‐10 (rho = 0.473, P = 0.002) and IFN‐γ and CXCL9 (rho = 0.403, P = 0.008) in the PTB group. However, in SevTB, only IFN‐γ and CXCL9 were positively associated (rho = 0.529, P = 0.016). Systemic levels of cytokines are reflective of local responses at disease sites. Therefore, our data suggests that in PTB increased IFN‐γ and CXCL9 balanced by IL‐10 may result in a more effective cell mediated response in the host. However, elevated inflammatory chemokines CXCL9 and CCL2 in severe EPul‐TB without concomitant down modulatory cytokines may exacerbate disease related pathology and hamper restriction of M. tuberculosis infection.