Antibody specificity refers to an antibody's ability to selectively bind to a unique epitope on a target antigen while avoiding interactions with unrelated antigens. This property arises from the highly specialized antigen-binding site located in the variable region of the antibody, which determines its unique binding characteristics.
While each antibody is designed to bind a single epitope, certain challenges arise. Proteins that share highly homologous regions may display similar epitopes, leading to cross-reactivity. For instance, a single antibody may recognize multiple proteins if these proteins share a conserved epitope. Similarly, antibodies derived from polyclonal serum may exhibit lower specificity due to the presence of multiple antibody clones targeting different epitopes or cross-reacting with unrelated antigens.
Mechanisms of Specificity
Antibody specificity is shaped by the molecular structure of the antigen-binding region, which includes six antigen-binding regions (ABRs). These regions correspond approximately to complementarity-determining regions (CDRs), long recognized as the critical zones in antigen recognition. The amino acid composition of each ABR influences its binding preferences, allowing it to interact with specific residues on the protein surface.
However, ABRs cannot fully distinguish epitopes from the rest of the protein surface. This limitation can cause challenges in predicting protein epitopes solely based on sequence or structural data.
Polyspecificity and Heterospecificity
Polyspecificity: Some antibodies can bind multiple distinct epitopes across different antigens. This property allows the immune system to recognize a wide range of antigens but can complicate antibody-based applications by increasing the likelihood of cross-reactivity.
Heterospecificity: Occurs when an antibody reacts more strongly with an antigen other than the one used for its elicitation. This phenomenon can lead to misinterpretations in research and highlights the need for rigorous specificity validation.
Mechanisms for multispecific ligand recognition by antibodies or other receptors. DOI:10.1002/jmr.2394
Enhancing Specificity
Monoclonal Antibody Production
Monoclonal antibodies are derived from a single B-cell clone, so they are uniform with high specificity. These antibodies are preferred for applications requiring detection of a single epitope, such as diagnostic assays and therapeutic development.
Polyclonal antibodies, derived from serum, contain a mix of antibodies targeting various epitopes. While their broader reactivity can be advantageous in certain applications, raw serum often has low specificity due to the presence of irrelevant antibodies. Affinity purification techniques can enrich the desired antibodies, enhancing specificity.
Recombinant Antibody Engineering
Advances in recombinant antibody technology allow for precise modification of binding regions to improve specificity. Techniques such as in vitroaffinity maturation can fine-tune the antibody's interaction with its target antigen.
