The present invention addresses the problem of providing a method for stimulating production of IL-10 which has immunosuppressive effects. The present invention also provides an IL-10 production stimulating agent, and an immunosuppressant which comprises the IL-10 production stimulating agent as an active ingredient. By allowing a formulating agent which comprises protein A of Staphylococcus aureus (SPA) and immunoglobulin G (IgG) to act on IL-10 producing cells, the amount of production of IL-10 increases and production of IL-10 is stimulated. IL-10 mainly acts on monocytic cells to down-regulate immune functions including production of inflammatory cytokines, and also indirectly shows inhibitory effects against lymphocytes via the monocytic cells. Consequently, the formulating agent which comprises SPA and IgG is an excellent IL-10 production stimulating agent and is also useful as an immunosuppressant since the formulating agent suppresses production of inflammatory cytokines and allergic cytokines.
