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).
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