Fetal Bovine Serum Supplementation Enhances Functional Consistency of IGRA Results in Bovine Tuberculosis Diagnostics

The interferon-gamma release assay (IGRA) is a reliable diagnostic tool for bovine tuberculosis (bTB) due to its high sensitivity and specificity. However, the assay relies on viable T-cell function, making it susceptible to functionally undetectable responses during sample storage. This study aimed to evaluate whether fetal bovine serum (FBS) supplementation could mitigate functional deterioration and stabilize immune responses in stored blood samples. The IGRA was conducted on blood samples from 91 cattle under three conditions: fresh (Day 0), stored without FBS (FBS X), and stored with 10% FBS (FBS O). A dual stimulation using bovine PPD (bovis) and mitogen revealed that the FBS O condition significantly preserved IFN-γ responses, with a higher frequency of simultaneous bovis and mitogen recovery (dual recovery). Additional correlation analysis between MTT cell viability and mitogen response further suggested that FBS contributes to T-cell functionality beyond survival. These findings suggest that FBS supplementation improves the functional consistency of IGRA results and reduces the risk of functionally undetectable responses in delayed testing scenarios.