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