Rabbit CD40 Ligand (CD40L), also known as CD154 and encoded by the CD40LG gene, is a type II transmembrane protein belonging to the tumor necrosis factor (TNF) superfamily, which includes related ligands such as TNF-α, CD27 ligand (CD70), OX40 ligand (CD252), and 4-1BB ligand (CD137L) that regulate immune activation and cell–cell signaling. In rabbits (Oryctolagus cuniculus), CD40L is primarily expressed on activated CD4⁺ T lymphocytes, and can also be detected on platelets and other activated immune cells following antigen stimulation. CD40L binds to its receptor CD40, which is expressed on B cells, dendritic cells, macrophages, and other antigen-presenting cells, triggering intracellular signaling pathways such as NF-κB and MAPK that promote B-cell activation, proliferation, immunoglobulin class switching, germinal center formation, and development of memory B cells. Through these mechanisms, rabbit CD40L plays an essential role in T cell–dependent antibody responses and regulation of adaptive immunity. Because rabbits are widely used as experimental models for immunology, infectious disease, and antibody production, rabbit CD40L is studied in vaccine development, host–pathogen interaction studies, and immune response research, helping to advance understanding of costimulatory signaling and humoral immune regulation.