Antigenic drift is this continuous process of genetic and antigenic change among flu strains. Nickel then binds to skin protein carriers creating an antigenic epitope. This site binds to a portion of the antigen called an antigenic determinant or epitope. Extraneous undesired specific fluorescence occurs when a targeted antigen is impure and contains antigenic contaminants. A hapten is a small molecule that changes the structure of an antigenic epitope. Antigenic variation is common among pathogenic organisms. "substances immunogenes ou antigenes" (antigenic or immunogenic substances). Many of the proteins known to show antigenic or phase variation are related to virulence. Disease-causing strains are classified according to the antigenic structure of their polysaccharide capsule. Then, the cells begin to display surface HIV glycoproteins, which are antigenic. Hypoallergenic infant formulas can be based on proteins partially predigested to a less antigenic form. They may directly activate B cells, regardless of their antigenic specificity. Many genes involved in antigenic variation are located in the subtelomeric regions of the chromosomes. Asian lineage HPAI A(H5N1) is divided into two antigenic clades. Pili are varied by antigenic variation, but also phase variation.