The present invention relates to compositions comprising nucleobases and/or sources of nucleobases and polysaccharides from extracts of fungi, yeasts or bacteria. Preferably, the compositions include Nucleoforce® or Nucleoforce® Dogs and AHCC®. Said compositions are useful in the treatment and prevention of immunosuppression, of the toxicity derived from chemotherapy or radiotherapy treatment, of diseases of the immune system, of cancer or an infection； and are also useful to stimulate the immune function in a mammal, including a human.
