Research paperConstitutive interaction between 4-1BB and 4-1BBL on murine LPS-activated bone marrow dendritic cells masks detection of 4-1BBL by TKS-1 but not 19H3 antibody

•The anti-4-1BBL antibodies TKS-1 and 19H3 bind to distinct sites on 4-1BBL.•The TKS-1 but not the 19H3 antibody binding site on 4-1BBL is masked by 4-1BB.•4-1BB can bind to 4-1BBL on an adjacent DC to block TKS-1 binding in trans.•4-1BB and 4-1BBL interact constitutively on LPS-activated bone marrow derived DC.•19H3 is the preferred antibody to use to detect 4-1BBL when 4-1BB is present.

4-1BB is a TNFR family member associated with NF-κB mediated survival signaling. 4-1BB is widely expressed on activated cells of the immune system, including activated T cells, NK cells and dendritic cells. Its ligand, 4-1BBL, is transiently expressed on activated antigen presenting cells and at low levels on activated T cells. Although 4-1BBL-deficient mice clearly demonstrate a role for 4-1BBL in CD8 T cell responses to viruses such as influenza, 4-1BBL can be difficult to detect following infection of mice. Here we provide evidence for a constitutive interaction between endogenous 4-1BB and 4-1BBL on LPS activated bone marrow-derived murine dendritic cells that can mask its detection, with implications for measurement of 4-1BBL expression. The masking of 4-1BBL by its receptor results in loss of reactivity to the anti-4-1BBL antibody TKS-1, whereas the 19H3 antibody binds to 4-1BBL in the presence or absence of 4-1BB. Moreover, 4-1BB/4-1BBL interaction can occur in trans between 4-1BB+/+ and 4-1BB−/− dendritic cells in culture. These data suggest that 19H3 is the preferable antibody to use to detect 4-1BBL in the presence of its receptor.

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