2. Molecular Diagnostic Reagents for Infectious Diseases

2.1 Latent Tuberculosis Infection Detection Reagents

Latent tuberculosis infection (LTBI) is defined as a state of persistent immune response to stimulation by Mycobacterium tuberculosis antigens with no evidence of clinically manifested active TB. There is no gold standard test for LTBI, and thus only a rough estimate of the number of infections can be made. One-third of the world’s population is estimated to be infected with M. tuberculosis. Many studies have shown that 5–10% of people with LTBI will subsequently develop active TB disease. Treating LTBI to prevent active TB disease has become a very important part to achieve the targets of the WHO’s End TB Strategy.

Testing LTBI is the first step in the treatment. Interferon-γ release assay (IGRA) and tuberculin skin test (TST) are the most commonly used methods to detect LTBI. The ability of these two methods to predict active TB is approximately equivalent. TST is an in vivo diagnostic method that detects hypersensitivity by intradermal injection of Mycobacterium antigen, with the disadvantage of cross-reactivity with BCG and environmental mycobacteria. IGRA is an in vitro diagnostic method that stimulates peripheral blood T-lymphocytes with M. tuberculosis-specific antigens. It will not produce false positive results when people have been vaccinated with BCG or encounter environmental mycobacteria. However, both IGRA and TST have low diagnostic sensitivity in young children and immunocompromised patients, such as those with HIV infection, corticosteroid treatment, and other immunosuppressive drugs. As a result, researchers have been searching for new markers for the detection of LTBI.

IFN-γ-induced protein 10 (IP-10) mRNA is a potential marker that has been studied in recent years. Its expression level is 100-fold higher than that of interferon-γ after antigen stimulation. The Mycobacterium Tuberculosis Specific Cellular Immunoreaction Detection Kit (PCR-Fluorescence) (Registration No.: G.X.Z.Z 20203400334) of Suzhou Chuanglan Bio-Tech Co., Ltd. is a qualitative kit that uses IP-10 mRNA as the target of the test and detects IP-10 mRNA levels before and after stimulating with TB-specific antigen by using an anticoagulated peripheral blood sample. This reagent will be used for the detection of LTBI.

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