Antigens are recognized by antigen receptors, including antibodies and T-cell receptors.Diverse antigen receptors are made by cells of the immune system so that each cell has a specificity for a single antigen. Upon exposure to an antigen, only the lymphocytes that recognize that antigen are activated and expanded, a process known as clonal selection.In most cases, antibodies are antigen-specific, meaning that an antibody can only react to and bind one specific antigen.The reaction between an antigen and an antibody is called the antigen-antibody reaction.ND-Antigen is specially designed for the disease of poultry ND, no other bad effect or immunosuppression.