Anti-mouse CD137L (4-1BBL) - PE (L326-GRP)

4-1BBL (CD137L) and 4-1BB (CD137) are a receptor ligand pair belonging to the tumor necrosis factor (TNF) receptor/TNF superfamily1,2. 4-1BBL is a type II transmembrane protein expressed by splenic B and T cells, macrophages, and dendritic cells1-5. Members of the TNF-TNF receptor superfamily play critical roles in regulating cellular activation, differentiation, and apoptosis6 and the 4-1BBL-4-1BB interaction is important in cellular immune responses5. 4-1BBL-4-1BB interaction provides a co-stimulatory signal to T cells, resulting in increased proliferation and cytokine production5. A TKS-1-producing hybridoma was generated by immunizing a SD rat with 4-1BBL-transfected NRK cells (rat IgG2a,κ)5. Splenocytes were fused with P3U1 cells and hypoxanthine–aminopterin–thymidine selection was performed. The monoclonal antibody was identified by its strong reactivity with 4-1BBL-transfected L5178Y cells, cloned by limiting diffusion, purified from ascites, and found to bind to 4-1BBL/NRK and 4-1BBL/P815 cells5. Pre-incubation with TKS-1 blocks 4-1BB–Ig binding to 4-1BBL/L5178Y cells, indicating TKS-1 is specific to mouse 4-1BBL and can interrupt the interaction between 4-1BBL and 4-1BB5. Additionally, TKS-1 can block anti-CD3-stimulated T cell proliferation co-stimulated by 4-1BBL /P815 cells. The monoclonal antibodies 19H3 and TKS-1 bind to different sites on murine 4-1BBL, with TKS-1 binding to a site that overlaps with the receptor binding site7. Additionally, TKS-1 and 4-1BB bind to a similar site, making TKS-1 especially useful for blocking studies.