PLGLB1 (plasminogen-like B1), also known as plasminogen-related protein B (PRP-B), is a 9-kDa protein structurally homologous to the N-terminal activation peptide of plasminogen 1. The gene is primarily expressed in liver tissue 1 and shows elevated transcription in neoplastic tissues 2. PLGLB1 functions as a potent angiogenesis inhibitor. Recombinant PLGLB1 antagonizes basic fibroblast growth factor-dependent migration of endothelial and smooth muscle cells, inhibits endothelial tube formation, and promotes cell attachment through interaction with α(v)-containing integrins 3. This anti-angiogenic mechanism contributes to tumor growth suppression in mouse xenograft models 2, with enhanced efficacy when combined with chemotherapy 4. Clinically, PLGLB1 demonstrates therapeutic potential in cancer and inflammatory disease. Recombinant PLGLB1 treatment effectively inhibited collagen-induced arthritis development in mice by reducing VEGF expression, vessel formation, and synoviocyte proliferation 5. In COVID-19 pathogenesis, serum PLGLB1 levels are significantly elevated in infected patients compared to controls and fail to normalize during convalescence, suggesting persistent anti-angiogenic effects and potential involvement in post-COVID complications 6. However, PLGLB1-mediated angiogenesis inhibition shows resistance to sphingosine 1-phosphate signaling, indicating limitations in certain pathological contexts 7.