A purified Arabinogalactan-Protein (AGP) composition isolated through a selective method from the leaves and/or stems of Argemone mexicana plant is described. Also described is a purified Arabinogalactan-Protein (AGP) composition isolated from the leaves and/or stems of Argemone mexicana plant, which has one or more of the following effects: immunosuppression, lymphoproliferation inhibition, cytokine modulation such as IL-2 inhibition, IFN-.gamma. inhibition, or IL-10 induction; keratinocyte proliferation inhibition, keratolytic activity and inhibitory activity in Mouse Ear Swelling test (MEST).