Blood consists of two major components, various kinds of cells and the fluid called serum. Serum consists of heterogeneous population of antibodies. Different antibodies are produced by different types of B-lymphocytes.

Hence, serum consists of different types of antibodies which are often called polyclonal antibodies. The antibodies bind to specific domains of antigens (called antigenic determinants or epitopes) and neutralise them.

1. Monoclonal Antibodies (MoAb) :

A single type of antibody directed against a specific epitope and produced by hybridoma cell line is called monoclonal antibodies (i.e. the preparation that contains identical antibodies).

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The plasma cells (the highly processed B-cells) produce antibodies IgM (red) and IgG (green), antibodies but never divide further. In contrast the myeloma cells (cancerous lymphocytes of bone marrow) never produce antibodies but divide rapidly in vitro.

In 1975, for the first time George Kohler and Cesar Milstein produced B-cells from spleen after immunising the mouse with antigen. They fused B-cells (antibody producing cells) and myeloma cells (cancerous cells) in the presence of polyethylene glycol (PEG). Consequently the B-cells became immortalised, antigenic determinant.

The fused cells were called hybrid cells or hybridoma. Hybridoma technology solved both of these difficulties. The hybrid cells have the properties of both the cells i.e. the ability of antibody secretion and indefinitely cell division.

When each j hybrid cell is grown in culture WS medium, it secretes epitope- specific anti-body which is called as S-10.5: Multinucleated cells showing fusion, monoclonal antibody.

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In recent years, production of MoAb is being done commercially by using large scale culture in air-lift fermentors or other bioreactors. About 50 mg/ml of antibody can be produced. Since 1980, hundreds of monoclonal antibodies have been commercially produced and available in market in the U.S.A., Europe and Asia including India.

Recently, biotechnology earned much popularity after the production of MoAb through hybridoma technology. Using this technology, you can create hybridomas that produce antibodies against almost any antigen.

However, it is possible to identify many different Antibodies secreted by hybridoma hybridomas that produce antibodies against a particular clones is called monoclonal antibodies, antigen. Each antibody recognises a different epitope or specific structural features of the antigen. Hence MoAbs are very specific.

2. Applications of Monoclonal Antibodies :

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The monoclonal antibodies are used in the four main ways i.e. disease diagnosis, disease treatment, passive immunisation and detection and purification of biomolecules. However, their exploitation for various uses is based on two features: (i) exacting the specificity of antibody binding, and (ii) presence of similar structure of all antibody molecules.

(a) Disease Diagnosis:

Using MoAb medical conditions and diseases of sufferers can be diagnosed. One of the approaches is the ‘antibody-sandwich’ strategy which is also called ELISA (enzyme- linked immunosorbent assay).

The circulatory antigens in blood can be assayed using ELISA or radio-immuno assay (RIA) technique. By using ELISA you can test HIV, hepatitis, typhoid, herpes, etc. For each test, separate ELISA kit is used.

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A preparation of monoclonal antibody is attached to the surface of a plastic dish called well. Then antigen-containing solution is added. The solution is washed to remove unbound antigens. A second monoclonal antibody preparation (attached with alkaline phosphatase or other enzyme) is added to the wells.

If the specific antigen is attached to the first MoAb, the second antibody will bind attaching the enzyme to the surface of the dish as an antibody-antigen-enzyme labelled antibody sandwich.

If there is no antigen, no enzyme will be attached. When substrate for enzyme is added, coloured product appears which confirms the presence of antigen.

ELISA is used to diagnose HIV, Cancer, Epstein-Barr virus as well as pregnancy testing, to check meat for the presence of pathogenic microbe (or their toxin) such as streptococcal pharyngitis.

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(b) Disease Treatment:

The MoAb has highly specific antigen-binding properties. This makes them ideal candidates for use in disease therapy.

Therapeutic Monoclonal Antibodies -OKT3:

Certain metabolic pathways are selectively blocked by the MoAb. If an antigen is present on cell membrane, it is neutralised by the specific antibody. Thus an antibody inactivates a ‘specific cell surface antigen’ present on T cells.

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Cell-mediated immune system (CMI) plays a key role during organ or bone marrow transplantation. T-cells of the CMI system rejects any of the foreign tissues transplanted. Therefore, patients undergo immunosuppressive therapy following organ transplantation.

The patients are given immuno-suppressive drugs to suppress T-cells. Otherwise the transplantation operation would get failed. The MoAb can be used selectively to eliminate T-cell population responsible for transplant rejection. This treatment has been successful in renal (kidney) transplantation.

CD3 is an antigen present on the surface of mature T- cells (lymphocytes). If T-cell population is depleted, the rejection of cellular transplanted organ does not occur.

An antibody that acts against CD3 surface antigen of T-cell is called OKT3 i.e. anti- CD3 MoAb. The OKT3 removes antigen-containing T-cells from blood circulation and from allograft (see Box 10.1). Hence, OKT3 can be used to prevent acute renal allograft rejection in humans. OKT3 has also been used to purge donor bone marrow prior to its use in marrow transplantation.

(c) Passive Immunisation:

Passive immunisation refers to transfer of antibodies from one individual to another. For example, administration of antivenom in the patients against snake-bite comes under this category.

Use of MoAb is done for passive immunisation against certain diseases. Approved MoAb-based drugs are already being used to treat septic shock (a set of symptoms appearing due to the presence of a particular toxin in the cell wall of many infectious bacteria).

(d) Detection and Purification of Biomolecules:

MoAb are very useful in determining the presence and quantity of specific proteins through Western Blotting technique. First the proteins from various samples are prepared and separated by polyacrilamide gel electrophoresis (PAGE). The protein bands are transferred onto a nitrocellulose filter.

The resulting Western blot is incubated with primary antibody. The antibody will bind if the specific antigen is present. This binding will allow a secondary antibody tagged to specific dye to be used to locate the first one. The Western blot is photographed to show the exact location of antigen as dark band.