Evaluation of the Immunomodulatory Properties of a Calf Lipid Thymus Extract and Standardization of a Method for Quantification of its Biological Activity

The aim of this study was to test the immunobiological properties of a new formulation of the lipid thymus calf extract (Thymsol), prepared for in vitro cell culture experiments. At first, we showed that Thymsol enhanced the antigen specific immune response in AO rats in vitro, using Keyhole limpet hemocyanin (KLH). At lower concentrations (0.5-2.5 μg mL^-1) the extract increased the proliferation of rat spleen lymphocytes in vitro, stimulated with suboptimal concentrations of Concanavalin A (ConA) or anti-T-cell receptor (TCR) monoclonal antibody (mAb), followed by an increase in the production of interleukin-2 (IL-2). Stimulation of IL-2 production was additionally enhanced in the presence of a blocking anti-IL-2 receptor α mAb. Higher concentrations of Thymsol (20-60 μg mL^-1) showed a dose-dependent inhibition of lymphocyte proliferation. After testing the variability in IL-2 production by anti-TCR mAb-activated splenocytes, using several stimulatory concentrations of different Thymsol samples, and the production of this cytokine by different cultures of splenocytes treated with the same Thymsol sample, we proposed an IL-2-based method for quantification of the immunobiological activity of the extract.