By Dr Ananya Mandal, MD
Use of antibodies in disease diagnosis and therapy
Antibodies are used extensively as diagnostic tools in many different formats. The term applied for antibody based diagnostic tests is “immunoassay”. Antibody-based immunoassays are the most commonly used confirmatory diagnostic assays and is the fastest growing technologies for the analysis of biomolecules.
Examples of immunoassay include titer of antibodies directed against Epstein-Barr virus or Lyme disease estimated from the blood. In absence of these antibodies it is presumed that either the person is not infected, or the infection occurred a ''very'' long time ago, and the B cells generating these specific antibodies have naturally decayed.
For immunoassays, levels of individual classes of immunoglobulins are measured by nephelometry (or turbidimetry) to characterize the antibody profile of patient. The Coombs test is also used for antibody screening in blood transfusion preparation. This test is used for antibody screening in antenatal women as well. Immunoassays are used in multiple sclerosis, psoriasis, and many forms of cancer including non-Hodgkin's lymphoma, colorectal cancer, head and neck cancer and breast cancer.
Then there is the use of radiolabelled antibodies that can be used in the diagnosis of diseases as well. These radiolabelled antibodies are used for diagnosis or detection of whole cells, receptors and enzymes. There is also enzyme labelled immune assays.
In the past, most immunoassays were based on polyclonal antisera drawn from immunized rabbits, which provided a good immune response despite having limited antigens. This changed with the advent of monoclonal antibodies, as described in 1975 by Köhler and Milstein.
Monoclonal antibodies revolutionized the use of antibodies in therapy called immunotherapeutics. Monoclonal antibodies have become a large part of immunodiagnostics as well.
Trends in antibody based diagnosis show advances in assay specificity, detection technologies and sensitivity. Sensitivity and specificity is ensured depending on whether or not the antigen to be quantified competes with labelled antigen for a limited number of antibody binding sites.
Flow cytometric analysis
Another important new technology with particular importance in diagnostics is flow cytometric analysis. This uses many new monoclonal antibodies against different cell-surface structures and helps flow cytometry in diagnosis if blood cancers. Flow cytometry has also more recently been used in the monitoring of disease and in the evaluation of tumor response to therapy.
Approved antibody preparations
As of 2011, 35 monoclonal antibody preparations have been approved by the U.S. Food and Drug Administration for use in humans. Some of these include:
- Muromonab-CD3 (OKT3) and two humanized anti-CD3 monoclonals. These are used in prevention acute graft rejection of organ, e.g., kidney transplants.
- Omalizumab (Xolair®) bind to IgE thus preventing IgE from binding to mast cells. Finds use in allergic asthma.
- Infliximab (Remicade®) and adalimumab (Humira®) – these bind to (TNF-α) and have been used in rheumatoid arthritis
- Daclizumab (Zenapax®) – binds to IL-2 receptor exposed at the surface of activated T cells. Used to prevent acute rejection of transplanted kidneys and in T cell lymphoma
- Rituximab binds to CD20 and used in Non Hodgkin’s lymphoma
- Heceptin – used in metastatic breast cancer
Antibodies during and before childbirth
Rhesus factor, also known as Rhesus D (RhD) antigen, is an antigen found on red blood cells. Presence of the antigen makes a person Rhesus-positive (Rh+) and absence makes a person Rhesus-negative (Rh–). During normal childbirth, delivery trauma or complications during pregnancy, blood from a fetus can enter the mother's system. In the case of an Rh-incompatible mother and child, there may be sensitization of an Rh- mother to the Rh antigen on the blood cells of the Rh+ child. This may put the remainder of the pregnancy, and any subsequent pregnancies at risk of fetal death due to hemolysis.
For treatment Rho antibodies (specific for human Rhesus D (RhD) antigen) are used. Anti-RhD antibodies are administered as part of a prenatal treatment regimen to prevent sensitization that may occur when a Rhesus-negative mother has a Rhesus-positive fetus.
Antibodies in industry
Antibodies are also used in structure prediction. This information is used for protein engineering, modifying the antigen binding affinity, and identifying an epitope, of a given antibody. X-ray crystallography is one commonly used method for determining antibody structures. This, however, is a difficult process. Computational approaches provide a cheaper and faster alternative to crystallography but results are more equivocal.
Antibodies are thus methods that can be used to predict structures of biomolecules. Online web servers such as ''Web Antibody Modeling'' (WAM) and ''Prediction of Immunoglobulin Structure'' (PIGS) enables computational modeling of antibody variable regions.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)