Immunogens are those antigens, termed immunogenic, capable of inducing an immune response. "substances immunogenes ou antigenes" (antigenic or immunogenic substances). The D antigen is the most immunogenic of all the non-ABO antigens. Exotoxins are extremely immunogenic meaning that they trigger the humoral response (antibodies target the toxin). The proteins are composed of a single immunogenic HLA allele . Lipid A is very pathogenic and not immunogenic. Some consider the cytotoxic and immunogenic theories together as a single "toxic" theory. A challenge in biotherapy is predicting the immunogenic potential of novel protein therapeutics. In recent years, a number of parasite proteins with immunogenic potential have been discovered. The vaccine is safe and immunogenic in mice, rabbits, and humans. For example, "S.cerevisiae" (yeast) often produce high-mannose glycans which are immunogenic. This is due to the protein carrier being highly immunogenic in nature. The cell dies by spilling its contents, mediating the distribution of further immunogenic molecules. For instance, necroptotic cells release highly immunogenic DAMPs, initiating adaptive immunity. HSV-TK is virus-derived and may be immunogenic to humans.