Withanolide, coagulin-H (1), was evaluated for its effect on various cellular functions related to immune response including lymphocyte proliferation, and expression of interleukin-2 (IL-2) cytokine, and results were compared with prednisolone (2), a commonly used immune modulating drug. Coagulin-H (1) was found to have a powerful inhibitory effect on lymphocyte proliferation and Th-1 cytokine production. Inhibition of the phytohaemagglutinin (PHA)-activated T-cell proliferation by coagulin-H (1) was observed in a concentration dependent manner. A complete suppression of PHA-activated T-cell was observed at > or =2.5 microg/mL concentrations of compound (1) and this suppression activity was similar to that of prednisolone (2). Coagulin-H (1) also significantly inhibited IL-2 production by 80%. The interactions of coagulin-H (1) (a natural inhibitor) and prednisolone (2) (a drug) to IL-2 were also investigated in order to understand the differences in their effects on T-cell responses. This paper also describes the results of molecular docking study on IL-2 inhibition. Docking studies predicted that coagulin-H (1) binds to receptor binding site of IL-2 more effectively than prednisolone (2). Based on the computational and the experimental results, coagulin-H (1) was identified as a potential immunosuppressive candidate.