To communicate between cells, the immune system employs hormone-like signal substances; transfer factors are one class of such immune system communication substances. Transfer factors include both inducer/helper functions (Inducer Factors) and regulator functions (Regulator Factors)—historically called "suppressor functions". The Inducer Factors translate an apparently mature immune response from the donor to the recipient. Regulator Factors help control overreactions and limit allergies and autoimmune conditions. Transfer factors have been shown to induce an immune response in less than 24 hours. Transfer factors are not species-specific, thus transfer factors produced by a cow's immune system are just as effective in humans as they are in the cow.