Serum siderocalin levels in patients with tuberculosis and HIV infection

OBJECTIVES: Mycobacterium tuberculosis produces high-affinity siderophores that play essential roles in iron acquisition and tuberculosis (TB) pathogenesis. In response, host cells secrete a siderophore-binding protein, siderocalin, to limit the bacteria’s access to iron. The objective of the present study was to evaluate the levels of siderocalin in patients with TB with or without HIV infection compared to controls. METHODS: Siderocalin levels were tested using a neutrophil gelatinase-associated lipocalin (NGAL) ELISA kit in four populations: HIV-infected patients with TB (HIV(pos), TB(pos)), non-HIV-infected patients with TB (HIV(neg), TB(pos)), HIV-infected patients without TB (HIV(pos), TB(neg)), and healthy controls (HIV(neg), TB(neg)). RESULTS: Serum siderocalin levels were significantly elevated in patients with TB regardless of their HIV status (HIV(neg), TB(pos) 920 (480–1050) pg/ml; HIV(pos), TB(pos) 494 (166–1050) pg/ml), whereas lower levels of siderocalin were seen in HIV-positive patients (HIV(pos),TB(neg)268 (77–937) pg/ml; HIV(neg), TB(neg) 453 (193–994) pg/ml). CONCLUSIONS: The results indicate that active TB leads to an up-regulation of serum siderocalin regardless of HIV status, whereas HIV infection leads to a down-regulation of serum siderocalin levels in both TB-negative and TB-positive individuals. Further studies are needed to evaluate siderocalin as a potential marker of active TB and to clarify its role in the pathogenesis of HIV-associated TB.