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

The tritium-labeled dipeptide bestim (gamma-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 (Kd 2.1 +/- 0.1 nM) and thymocytes (Kd 3.1 +/- 0.2 nM), as well as with plasma membranes isolated from these cells (Kd 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) (Ki 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.