Interaction of the synthetic immunomodulatory dipeptide bestim with murine macrophages and thymocytes

The tritium-labeled dipeptide bestim (γ-D-Glu-L-Trp) with a specific activity of 45 Ci/mmol was obtained by high-temperature solid-state catalytic isotope exchange. It was found that ³H]bestim binds with a high affinity to murine peritoneal macrophages (K _d 2.1 ± 0.1 nM) and thymocytes (K _d 3.1 ± 0.2 nM), as well as with plasma membranes isolated from these cells (K _d 18.6 ± 0.2 and 16.7 ± 0.3 nM, respectively). The specific binding of ³H]bestim to macrophages and thymocytes was inhibited by the unlabeled dipeptide thymogen (L-Glu-L-Trp) (K _i 0.9 ± 0.1 and 1.1 ± 0.1 nM, respectively). After treatment with trypsin, macrophages and thymocytes lost the ability to bind ³H]bestim. Bestim in the concentration range of 10^?10 to 10^?6 M reduced the adenylate cyclase activity in the membranes of murine macrophages and thymocytes.