Background: Several medicinal plants have shown anti-proliferative and apoptotic effects on human lymphocytes. In the present study the immunomodulatory properties of Stachys obtusicrena, a native plant to Iran, was examined and its possible effects on the induction of apoptosis were determined.
Material/Methods:The in vivo effect of the methanolic extract of S. obtusicrena on delayed type hypersensitivity (DTH) and antibody production was investigated in mice immunized with the antigen. The proliferation of human lymphocytes stimulated with mitogen in the presence of the extract was determined by [[sup]3[/sup]H]-thymidine incorporation assay. Mitogen-treated lymphocytes were exposed to the extract and analyzed for induction of apoptosis using flow cytometry and gel electrophoresis.
Results: Data obtained from the DTH and antibody responses indicated a dose-related decrease in both parameters in the extract-treated mice compared with the untreated control group. In the in vitro study performed on the lymphocytes, the extract caused a dose-dependent decline in [[sup]3[/sup]H]-thymidine uptake. The stimulation index of all cultures treated with different concentrations of the extract was less than 1. IL-2 levels in the culture supernatants of the activated lymphocytes showed a dose-related decrease as well. Results of flow cytometry indicated a dose-dependent accumulation of cells in the sub-G1 phase. The internucleosomal DNA fragmentation study showed typical DNA laddering in agarose gels.
Conclusions: The present study showed inhibitory effects of S. obtusicrena on both cellular and humoral immune responses and suggests that this effect may in part be due to the induction of apoptosis in proliferative lymphocytes.

Keywords: Stachys - immunology, Skin Tests, Plant Extracts - pharmacology, Phytohemagglutinins - pharmacology, Lymphocytes - drug effects, Interleukin-2 - metabolism, Hypersensitivity, Delayed - pathology, Dose-Response Relationship, Immunologic, DNA Fragmentation - drug effects, Cell Proliferation - drug effects, Antibody Formation - immunology, Stachys - immunology, Skin Tests, Plant Extracts - pharmacology, Phytohemagglutinins - pharmacology, Lymphocytes - drug effects, Interleukin-2 - metabolism, Hypersensitivity, Delayed - pathology, Dose-Response Relationship, Immunologic, DNA Fragmentation - drug effects, Cell Proliferation - drug effects, Antibody Formation - immunology