Box 1 | Glossary
Polyclonal antibody (First generation antibody): composed of biochemically distinct paratopes, the antigen-binding sites on the extended arm of the antibody, capable of specifically binding to different binding sites on the same antigen (Lipman et al., 2005). Monoclonal antibody (Second generation antibody): an immunoglobulin secreted from a single B lymphocyte clone and specifically recognizes a single epitope of an antigen (Nelson et al., 2000). Genetically engineered antibody fragments (Third generation antibody): also known as recombinant antibodies, antibody molecules expressed by transfecting appropriate recipient cells with genes encoding antibodies that have been modified and reassembled according to different needs using recombinant DNA and protein engineering techniques (Moore, 1989; Wright et al., 1992). For example, chimeric antibody, humanized antibody, fully humanized antibodies, single-chain variable fragment (scFv), and bispecific antibody (BsAb) are representatives of the genetically engineered antibody fragments. Synthetic antibody: affinity reagents, which provide therapeutics and diagnostics, engineered entirely in vitro, the production, selection, maturity or application is no longer limited by the natural immune system (Adams & Sidhu, 2014). Antibody mimetics (Fourth generation antibody): compounds that act similarly to antibodies and bind specific antigens; they are artificial polypeptides and are not related to antibodies (Zhang & Diraviyam, 2017). Peptide: short chain of amino acids linked by peptide (amide) bonds; naturally occurring molecules that regulate many signaling pathways in the body (Fosgerau & Hoffmann, 2015). Peptidomimetics: modified peptides; leading peptides are optimized by introducing functional modifications that can address the inherent shortcomings of the peptide while maintaining the structural features responsible for the biological activity (Lenci & Trabocchi, 2020). Affibody: one of the extensively used antibody mimetics with a protein scaffold derived from the B region of staphylococcal protein A; the B region consists of 58 amino acids that form into 3 alpha-helices recognizing the Fc domain of IgG (Ståhl et al., 2017). Peptide aptamer: short peptide sequences with an inert and rigid scaffold; they can be generated for low molecular weight targets, including small molecule ligands (Stojanovic et al., 2001; Yang et al., 2014) or even metal ions (Qu et al., 2016). Affimer: aptamers with improved performance; representing complementary affinity reagents for antibodies used in a variety of molecular and cellular biology applications (Tiede et al., 2017).