Introduction: There is evidence that the innate immune system is involved during Mycobacterium tuberculosis infection. In response against invading pathogens, the levels of many proteins inside the host change. Changes in the levels of these biomarkers can be used to aids in the diagnosis and monitoring of treatment response of MTB patients. Methodology: An Explorer antibody array containing 656 of antibodies were used identify the baseline and subsequent concentrations of Bax/Bcl-XL in plasma of 9 patients with no active disease at baseline but eventually developed active TB and 7 patients with active MTB at baseline. The Bax/Bcl-XL concentration and ratio over time were also observed in the plasma of C57BL6 mice infected via aerosol challenge with MTB K-strain. Result: In the subset of 9 patients who did not have tuberculosis at baseline but eventually developed the active disease, the Bax/Bcl-XL levels of those who developed active disease seem to be higher than those who developed the disease at a later time. Among the 7 patients with active disease at baseline, the Bax/Bcl-xL ratio levels decreased over time with antituberculosis treatment. In the mice model, the ratio of Bax/Bcl-xL increased one day after infection, significantly decreased by Day 2, and then gradually increased thereafter until Day 21. Conclusion: Bax/Bcl-XL ratio is a very promising bio-marker for the diagnosis and treatment response in tuberculosis. Additional experiments with longer follow-up time are recommended to understand the immune response in active TB in different subpopulations. Introduction: There is evidence that the innate immune system is involved during Mycobacterium tuberculosis infection. In response against invading pathogens, the levels of many proteins inside the host change. Changes in the levels of these biomarkers can be used to aids in the diagnosis and monitoring of treatment response of MTB patients. Methodology: An Explorer antibody array containing 656 of antibodies were used identify the baseline and subsequent concentrations of Bax/Bcl-XL in plasma of 9 patients with no active disease at baseline but eventually developed active TB and 7 patients with active MTB at baseline. The Bax/Bcl-XL concentration and ratio over time were also observed in the plasma of C57BL6 mice infected via aerosol challenge with MTB K-strain. Result: In the subset of 9 patients who did not have tuberculosis at baseline but eventually developed the active disease, the Bax/Bcl-XL levels of those who developed active disease seem to be higher than those who developed the disease at a later time. Among the 7 patients with active disease at baseline, the Bax/Bcl-xL ratio levels decreased over time with antituberculosis treatment. In the mice model, the ratio of Bax/Bcl-xL increased one day after infection, significantly decreased by Day 2, and then gradually increased thereafter until Day 21. Conclusion: Bax/Bcl-XL ratio is a very promising bio-marker for the diagnosis and treatment response in tuberculosis. Additional experiments with longer follow-up time are recommended to understand the immune response in active TB in different subpopulations.