The level of the endoplasmic reticulum stress chaperone protein, binding immunoglobulin protein (BiP), decreases following successful tuberculosis treatment

An increased Mycobacterium tuberculosis burden inside the host leads to higher demand of response proteins. This in turn results in metabolic shift and cellular stress, which is caused by the accumulation and trafficking of these proteins within the endoplasmic reticulum (ER). To resolve this, cells trigger the unfolded protein response (UPR), which is mainly mediated by binding immunoglobulin protein (BiP)/glucose-regulated protein 78 (GRP78) chaperone, and this in turn upregulates its transcription. This chaperone protein facilitates proper protein folding within the ER; however, it can also be passively secreted into the extracellular environment or be expressed on cell surfaces attached to anchor proteins and transmembrane proteins. This notion has been shown in studies on chronic inflammation, including cancer and arthritis, with the detection of BiP-specific antibodies from different sample types. The present study analysed secreted BiP from plasma samples collected from healthy participants and patients with newly diagnosed tuberculosis (TBdx), seen over the course of TB treatment at week 1 (W1), month 2 (M2), and month 6 (M6). The results revealed that during the initial TB disease and treatment period, cells are subjected to stress conditions resulting in metabolic shifts, which lead to the secretion of the intracellular UPR-mediating chaperone protein, BiP. This was indicated by mean differences between TBdx (mean 40.88ng/ml) and W1 (68.57ng/ml) in the TB participant groups. However, no difference was observed between the healthy group (mean 42.64ng/ml) and TBdx group (mean 40.88ng/ml). Analysis of paired time-point visits revealed increased BiP secretion during early TB treatment. The detection of BiP in plasma samples was found to decrease after successful TB treatment to levels comparable to those in the healthy controls. Evaluation of BiP levels in larger TB treatment studies may lead to the identification of a new target for early TB diagnosis and host-directed immunotherapy.