I. Monoclonal Antibodies

(1) Monoclonal Antibodies

Monoclonal antibodies are highly homogeneous antibodies produced by a single B-cell clone, targeting only one specific antigenic epitope. They are typically prepared using hybridoma technology. The hybridoma technique is based on cell fusion technology, which combines antigen-sensitized B cells capable of secreting specific antibodies with immortal myeloma cells to generate B-cell hybridomas.

In 1975, molecular biologists G.J.F. Köhler and C. Milstein developed the hybridoma technique based on natural hybridization methods. They fused mouse myeloma cells (which can be cultured and proliferated indefinitely in vitro) with B cells from antigen-immunized inbred mice, creating a hybrid cell line. This hybridoma retains the myeloma cells' ability to proliferate indefinitely in vitro while maintaining the antibody-producing cells' capacity to synthesize and secrete specific antibodies.By culturing these hybridomas as single-cell clones, monoclonal cell lines are established. Through in vitro culture or intraperitoneal inoculation in mice, large quantities of highly concentrated, exceptionally uniform antibodies can be obtained. These antibodies exhibit consistent structure, amino acid sequence, and specificity. Moreover, as long as no mutations occur during cultivation, the antibodies produced at different time points maintain identical structure and function. Such monoclonal antibodies cannot be obtained through other methods.

(2) Advantages and Limitations

1. Advantages of Monoclonal Antibodies

(1) Hybridomas can survive and proliferate indefinitely in vitro. As long as no genetic mutation occurs in the cell line, they can continuously produce antibodies with high specificity and homogeneity.

(2) Highly specific and uniform antibodies can be obtained in large quantities even when using relatively impure antigens.

(3) The potential to produce an "unlimited" supply of homogeneous antibodies makes monoclonal antibodies particularly suitable for immunological assays that rely on labeled antibodies, such as IRMA and ELISA.

(4) Due to their high specificity and single biological function, monoclonal antibodies are valuable for in vivo applications like radioimmunoimaging and immunotargeted therapy.

2. Limitations of Monoclonal Antibodies

(1) The inherent affinity constraints and limited biological activity of monoclonal antibodies restrict their application scope. Since monoclonal antibodies cannot form precipitates or agglutination reactions, many detection methods cannot be performed using monoclonal antibodies alone.

(2) The reaction intensity of monoclonal antibodies is generally weaker compared to polyclonal antibodies.

(3) The production process is technologically complex, time-consuming and labor-intensive, resulting in higher costs for monoclonal antibodies.

(3) Applications

1. Diagnostic Reagents in Laboratory Medicine

As diagnostic reagents in clinical laboratory medicine, monoclonal antibodies are widely used in techniques such as enzyme-linked immunosorbent assays (ELISA), radioimmunoassays, immunohistochemistry, and flow cytometry due to their advantages of high specificity, purity, and homogeneity. Moreover, the application of monoclonal antibodies has significantly contributed to the development of commercial diagnostic kits.

2. Protein Purification

Monoclonal antibodies serve as critical ligands in affinity chromatography. The antibodies are immobilized onto an inert solid-phase matrix (such as Sepharose 2B, 4B, or 6B) to prepare a chromatography column. When a sample passes through the column, the target antigen specifically binds to the immobilized monoclonal antibodies, while other components flow through. After thorough washing of the column, the bound antigen is eluted by altering the ionic strength or pH of the buffer. The eluate containing the purified antigen can then be collected.

3. Targeted Therapy and Radioimmunoimaging of Tumors

Targeted therapy of tumors refers to the approach where monoclonal antibodies specific to a tumor antigen are conjugated with chemotherapeutic drugs or radioactive substances. Utilizing the targeting capability of monoclonal antibodies, these therapeutic agents are delivered directly to the target organ to kill tumor cells. Additionally, by labeling monoclonal antibodies with radionuclides and administering them into the patient's body, radioimmunoimaging can be performed to aid in tumor diagnosis.Currently, most monoclonal antibodies used are murine-derived, and heterologous animal serum can cause allergic reactions in humans. Therefore, the development of human-human monoclonal antibodies or humanized antibodies is of greater importance. However, significant progress in this area has yet to be achieved.

II. Polyclonal Antibodies

(1) Polyclonal Antibodies

When an organism is stimulated by multiple antigenic determinants, it produces a variety of corresponding monoclonal antibodies. The mixture of these monoclonal antibodies constitutes polyclonal antibodies. In fact, the antibodies naturally produced in the body are polyclonal.In addition to the diversity of antigenic determinants, a single antigenic determinant can also stimulate the production of five classes of antibodies: IgG, IgM, IgA, IgE, and IgD. Compared to monoclonal antibodies, large-scale production of polyclonal antibodies is relatively rapid and cost-effective. However, they are nonspecific because they can recognize multiple epitopes on a given antigen.

(2) Advantages and Limitations

1. Advantages of Polyclonal Antibodies

(1) Can help enhance WB signals as the antibodies will bind to multiple epitopes.

(2) Due to recognition of multiple epitopes, polyclonal antibodies can provide better results in IP/ChIP assays.

(3) More tolerant of minor variations in the antigen, such as polymorphisms, glycosylation heterogeneity, or mild denaturation.

(4) Useful when the nature of the antigen is unknown.

(5) Lower production costs and shorter production time.

2. Disadvantages of Polyclonal Antibodies

(1) More prone to batch-to-batch variability.

(2) The recognition of multiple epitopes makes it important to check the immunogen sequence for any potential cross-reactivity.

(3) Applications

A high-quality polyclonal antiserum contains multiple antibodies targeting different epitopes of a specific antigen. Since polyclonal antisera typically consist of antibodies recognizing various epitopes of an antigen—including denaturation-resistant epitopes—they remain effective even in deeply fixed samples. As a result, polyclonal antibodies are often preferred for staining paraffin-embedded tissue sections. Depending on experimental requirements, polyclonal antibodies can be used to label target antigens accordingly.Additionally, in agricultural production, polyclonal antibodies are employed for on-site monitoring of pesticide residues. In clinical applications, they are primarily used for pathogen detection, disease diagnosis, and treatment. For instance, they serve as protein-based immunosuppressants in managing transplant rejection and autoimmune diseases.

III.  Comparison of Preparation Processes Between Monoclonal and Polyclonal Antibodies

 To produce monoclonal antibodies, B lymphocytes that have been exposed to a specific antigen are fused with myeloma cells via cell fusion, resulting in hybridoma cells.  These hybridomas are then screened using HAT medium, and their antibody titers are tested via ELISA to identify positive clones.  The selected clones are either cultured in vitro or injected into the peritoneal cavity of an animal (typically BALB/c mice) for ascites production.  The supernatant or ascitic fluid is then collected and purified to obtain monoclonal antibodies.In contrast, the preparation of polyclonal antibodies is less complex.  The antigen (preferably of high purity) is directly injected into an animal for immunization.  After 3 to 4 rounds of immunization, the antibody titer is tested by ELISA.  Once the titer meets the required standard, blood is collected and centrifuged to obtain the serum, which is then purified to yield polyclonal antibodies.  As a result, the production cycle for polyclonal antibodies is shorter than that for monoclonal antibodies, and the initial production cost is also lower.