IP-10 is an additional marker to evaluate the RD1-specific responses in HIV-infected subjects

Background: The suboptimal sensitivity of IFN-γ-based assays, especially in immunocompromised individuals, emphasizes the need for alternative markers for diagnosing tuberculosis (TB). Objective of this study was to evaluate whether IP-10 can be a useful biomarker for evaluating a specific response to RD1 antigens associated to active TB in HIV-infected individuals. Control with QuantiFERON-TB Gold In tube (QFT-IT) was performed. Methodology: 118 HIV-infected individuals were prospectively enrolled in Rome, 21 with active-TB and 98 without. Epidemiological characteristics were analyzed. IFN-γ and IP-10 response to QFT-IT was performed. Plasma was harvested at day-1 and soluble factors evaluated by ELISA. Results: Significant differences between those with or without active TB were found for the CD4+ T cell counts (p=0.02), and IFN-γ and IP-10 response to QFT-IT (p=0.001 for both analysis). Differently no significant differences were found for the age and HIV-RNA. Based on the commercial cut-off of the QFT-IT and on a cut-off found by ROC analysis for the IP-10-based responses, the sensitivity for active TB of QFT-IT and the IP-10 to QFT-IT was 52% and 67% respectively (p=0.001; K: 0.545). The response to IP-10 was not influenced by the ability to respond to the mitogen. The specificity for active TB of QFT-IT and of the experimental test were 84% and 77% respectively (p=0.01; k:0.710). Among those without active TB a significant correlation between a positive score and Mtb exposure was found (p<0.001). Conclusions: These data suggest that IP-10 is an additional marker to evaluate the RD1-specific responses in HIV-subjects confirming data previously obtained in high TB endemic countries.