Antigen specificity is due primarily to the side-chain conformations of the antigen. These membrane-bound protein complexes have antibodies which are specific for antigen detection. Different antibodies have the potential to discriminate among specific epitopes present on the antigen surface. IgE antibodies are typically specific to one particular antigen. Pleomorphic pattern is caused by antibodies to the proliferating cell nuclear antigen. Performing an ELISA involves at least one antibody with specificity for a particular antigen. The labeled antigen competes for primary antibody binding sites with the sample antigen (unlabeled). After immobilizing single-domain antibodies on sensor surfaces sensing human prostate-specific antigen (hPSA) were tested. Serotyping is done by mixing cells with antibodies for a particular antigen. The antigen of anti-dsDNA antibodies is double stranded DNA. The cells involved in recognizing the antigen are Lymphocytes. Proliferating cell nuclear antigen (PCNA) is a protein involved in DNA synthesis. This provides signal amplification by increasing the number of fluorophore molecules per antigen. It is the first detectable viral antigen to appear during infection. After activation by antigen, these B cells proliferate.