The inability of one’s own innate, and then acquired, immunity to ensure the elimination of foreign antigens and their carriers leads to additional stimulation by Th17 responses of innate immunity. Excessive stimulation by Th17 can lead to the development of autoimmune diseases. Autoimmune diseases can also be caused by excessive formation of products of catabolism of nucleic acids (purine mononucleotides and their metabolites). Tumor cells which have lost peptide copies of tissue-specific MHC class I antigens (HLA analogues), on the contrary, turn out to be unavailable for elimination by acquired immunity.