Exogenous binding immunoglobulin protein (BiP) enhance immune regulatory phenotype in ex-vivo Mtb infected PBMCs stratified based on QuantiFERON response

Abstract

Even though anti-tuberculosis (TB) treatment is readily available, Mycobacterium tuberculosis (Mtb) infection continues to be a global threat with a high death rate recorded from a single infectious agent. This highlights the significance of developing new strategies to curb the growing Mtb infection cases. Host-directed therapies (HDT) offer a promising approach that includes both drug discovery and drug repurposing, aimed at identifying host targets and promoting immune cell populations that can lead to better infection outcomes. In this context, we investigated the potential of exogenous Binding Immunoglobulin Protein (BiP) to induce such changes ex-vivo using PBMCs from healthy (QFN-) and Mtb exposed (QFN+) individuals. We analysed cell surface expression and cytokine profiles across eight different stimulation conditions including human full-length BiP protein (20 μg/ml), TLR-9a (0.5 μM), BiP/TLR-9a combination, isoniazid (1 μM), H37Rv (MOI: 1: 10), and pooled bronchoalveolar lavage (BAL) samples collected at TB diagnosis (TBdx) and at month 6 (M6) of anti-TB treatment. Our results revealed that BiP-stimulated PBMCs showed a significant reduction of interleukin (IL)-10 secretion, along with increased IL-4, IL-5, IL-13, and soluble Fas-L (sFasL) secretion. We also observed that BiP stimulation enhanced the expression of membrane bound Fas-L (CD178) and IL5Ra (CD125) in B-cells isolated from both QFN- and QFN+ groups. Additionally, BiP exhibited a synergistic effect with TLR-9a, further boosting this co-expression. Moreover, we observed that BiP induced IL5Ra expression in both CD3⁺CD5^lo and CD3⁺CD5^hi T-cell populations. This study explores the effects of exogenous BiP on cell functionality and provides valuable insights into its potential to modulate host cell responses, which could be explored as a host-directed therapy for TB in the future.