Nikolas
Created page with "thumb|The sensitization phase The purple molecule on the <abbr>CD4</abbr>+ cell is the <abbr>TCR</abbr>, and it binds to the red MHC class II receptor on the APC. Certain pathogens (all are intracellular bacteria or viruses) and contact antigens cause an immune reaction called hypersensitivity type IV or ''delayed-type hypersensitivity''. Some examples are m. tuberculosis, c. albicans, herpex simplex virus..."