Lienal Polypeptide Decreases Immune Thrombocytopenia in a Mouse Model by Upregulating Cytokine Production and Increasing the Levels of CD4 ⁺ , CD8 ⁺ , and T Regulatory Cells

Primary immune thrombocytopenia (ITP) is a condition marked by immune-mediated inadequate platelet production or excessive destruction. This study investigates the effects of Lienal polypeptide injection (LP) on T lymphocyte subgroups in the spleen and thymus, megakaryocyte counts in the bone marrow, and cytokine levels related to megakaryocyte development in mice with antibody-induced ITP, aiming to elucidate potential therapeutic mechanisms. We first assessed the effects of LP on Meg-01 megakaryocytic cells regarding proliferation, apoptosis, and differentiation using Methylthiazolyldiphenyl-tetrazolium bromide (MTT) assays, Western blot analysis, and flow cytometry for apoptosis and CD41 expression as a differentiation marker. Following this, LP was administered intraperitoneally at 60 mg/(kg·d) for 11 days to ITP mice. We quantified peripheral blood platelets and bone marrow megakaryocytes, measured spleen and thymus indices, and assessed serum levels of stem cell factor (SCF), interleukin-3 (IL-3), interleukin-6 (IL-6), and platelet factor-4 (PF-4) via enzyme-linked immunosorbent assay (ELISA). Flow cytometry quantified T-helper cells (CD4⁺), cytotoxic T cells (CD8⁺), and regulatory T cells (Tregs). LP significantly induced apoptosis in Meg-01 cells while not markedly affecting differentiation. In ITP mice, LP effectively prevented platelet decline without affecting megakaryocyte counts or maturity. Increased SCF, IL-3, and IL-6 levels, alongside decreased PF-4 levels, correlated with enhanced platelet production. Moreover, CD4⁺/CD8⁺ ratios and Treg populations increased, contributing to reduced platelet destruction. In conclusion, LP exerts a protective effect in ITP by modulating SCF, IL-3, IL-6, and PF-4 levels and restoring the balance of T cell subtypes, elucidating its therapeutic potential.