Plasma exosomes reveal insights into bovine tuberculosis pathogenesis and diagnostic opportunities.

Bovine tuberculosis (bTB) is a chronic infectious disease caused by the Mycobacterium bovis (M. bovis). Rapid, cost-effective, and accurate diagnosis of bTB remains a significant clinical challenge globally. In this study, we performed a comprehensive proteomic analysis to evaluate the discriminatory power of plasma and plasma exosomes for bTB diagnosis. We compared protein expression profiles across three groups: M. bovis-negative controls (bTB_N, n = 10), M. bovis-positive cases (bTB_P, n = 10), and co-infected animals (Other_P, n = 10) with Brucella, infectious bovine rhinotracheitis virus (IBRV), and bovine viral diarrhea-mucosal disease virus (BVDV). Quantitative analysis identified 3820 exosomal proteins-2.27-fold more than the 1686 plasma proteins detected. Exosomal proteins exhibited superior sample clustering and discriminative capacity for infected groups. Notably, 227 plasma and 861 exosome-derived proteins were uniquely differentially expressed in bTB (bTB-specific DEPs). Pathway enrichment analysis revealed that exosome-specific DEPs were significantly enriched in TB-related pathways, including neutrophil extracellular trap (NET) formation, endocytosis, and tuberculosis, exhibiting greater biological relevance compared to plasma-specific DEPs. Furthermore, eight candidate proteins (APOE, FBLN5, VDAC1, ABCE1, LMAN1, PLG, SPP1, and SRP9) demonstrated high specificity for bTB discrimination, with two (FBLN5 and SPP1) displaying stage-specific expression patterns during M. bovis infection. This study underscore plasma exosome as a highly promising source of biomarkers for bTB diagnosis, offering enhanced sensitivity and deeper mechanistic insights over conventional plasma proteome.