Three main types of antibodies can be produced: polyclonal, monoclonal and recombinant. Each of these antibody types has advantages, but also limitations, and they should thus be viewed as complementary to each other, as each is particularly useful in specific areas (see comparison in Table 1).

Table1. Comparison of polyclonal and monoclonal antibodies

Polyclonal antibodies are produced in animals by injecting them with antigen and biochemically recovering the antibodies from the animal blood serum. Polyclonal antibodies are essentially a population of antibody molecules contributed by many B cell clones. The multiple B cell lineages involved produce a range of antibodies to many different epitopes, all binding the same original antigen. Mammals produce antibodies to practically any foreign protein, providing it has a molecular mass greater than 5000 Da and the antigen is not closely related to substances found in the animal itself. Many mammalian proteins and other biochemical substances are highly con served and thus elicit a very similar immune response in many species. This can lead to problems in producing antibodies for diagnostic and therapeutic use. As discussed, the immune system does not generally mount a response to self and because of this, if the antigen donor and antibody-producing host are closely related species, some anti gens may not raise an antibody response. Historically, the first antibodies produced artificially for diagnostic purposes were polyclonal. They are generated in a number of animal species by immunising the host with the substance of interest, usually three or four times. Blood is collected and serum tested at regular intervals; when the antibody titre is high enough, the antibody fraction is purified from the blood serum. Generally, larger animals are used, since bigger volumes can be obtained from larger species. The use of polyclonal antibodies in therapeutics is limited, as they themselves can be antigenic when injected into other animals. Polyclonal antibodies are cheap to produce, robust, but often less specific than other antibodies and therefore have variable qualities depending on the batch, as well as the specific donor animal.

Monoclonal antibodies (monoclonals) are produced in tissue culture by cells originating from a single hybridoma , a cell line stemming from the fusion of a single immortal mammalian cancer cell with a single antibody-producing B cell. B lymphocytes have a limited lifespan in tissue culture, but the cloned hybridoma has immortality conferred by the tumour parent and continues to produce antibody. In contrast to whole-antigen-specific polyclonal antibodies produced by multiple immune cells, monoclonals are specific to single epitopes and are produced by clonal cells. This difference (summarised in Table 1) is fundamental to the way in which monoclonal antibodies can be used for both diagnostics and therapeutics. Once cloned, the hybridoma cell lines are reasonably stable and can be cultured to produce large quantities of antibody, which they secrete into the culture medium. The antibody they produce has the same properties as the parent lymphocyte and it is this uniqueness that makes monoclonal antibodies so useful. As monoclonal antibodies are epitope specific and there are thousands of potential epitopes on an average antigen, a cell fusion process generates many hundreds of hybridoma clones, each making an individual antibody. Consequently, to ensure that the antibodies produced have the correct qualities needed for the final intended use, the screening process that is used to select the clones of value is the most important part of making hybridomas. Monoclonal antibodies can be used for human and veterinary therapeutics; however, they can be themselves antigenic, i.e. while structurally similar, the differences between murine and human antibody proteins can invoke an immune response against mouse- specific epitopes when murine monoclonal antibodies are injected into humans. This can result in their rapid clearance from the recipients' blood, systemic inflammation and the pro duction of human anti-mouse antibodies. Chimeric or humanised hybridomas can be engineered by joining mouse DNA encoding the binding portion of a monoclonal antibody with human antibody-encoding DNA. This construct can be cloned into an immortal cell to produce an antibody that will recognise human epitopes, but not be immunogenic when injected into humans. Transgenic mouse technology is the most successful approach to generate human monoclonal antibody therapeutics. Humanised antibodies have been used very successfully for treating a range of human conditions, including breast cancer, lymphoma and rejection symptoms after organ transplantation.

Recombinant antibodies are commonly generated by molecular methodologies in either prokaryotic or eukaryotic expression systems. The idea of producing antibodies in crop plants is attractive, as the costs of growing are negligible and the amounts of antibody produced could be very large. Expression in plants has had some initial success.

Two methods are most commonly used to produce recombinant antibodies. DNA libraries can be used to produce a bacteriophage expressing antibody fragments on the surface. Useful antibodies can be identified by assay and the bacteriophage producing it is then used to transfect the antibody DNA into bacteria for expression in culture by the recombinant cells. The antibodies produced are monoclonal, but do not have the full structure of those expressed by animals or cell lines derived from animals. They are less robust and as they are much smaller than native antibodies it may not be possible to modify them without losing binding function. However, the great advantage of using this system is the speed with which antibodies can be generated, generally in a matter of weeks. In contrast, the typical timescale for producing mono clonal antibodies from cell fusions is about 6 months.

Antibodies can also be generated from donor lymphocyte (B cell) DNA. The highest concentration of B cells is found in the spleen after immunisation and so this is the tissue usually used for DNA extraction. The antibody-coding genes are then selectively amplified by polymerase chain reaction ( PCR) and transfected into the genome of a eukaryotic cell line, whereupon a small percentage of cells will incorporate the PCR product into the genomic DNA. Usually, a resistance gene is cotransfected so that only recombinant cells containing antibody genes will grow in culture. The cells chosen for this work are often those most easily grown in culture and may be rodent or other mammalian lines. Typically, Chinese hamster ovary (CHO) cells are used for recombinant antibody production and have in fact become the industry standard amongst biotechnology companies. Yeasts, filamentous algae and insect cells have also been used as recipients for antibody genes, albeit with varying degrees of success.

اخر الاخبار

اخبار العتبة العباسية المقدسة

دار علوم نهج البلاغة تقيم محفلها الفكريّ الأسبوعي في ذي قار

العتبة العباسية المقدسة تناقش استعداداتها لحفل إزاحة الستار عن الطبعة الأولى من مصحف النجف الأشرف

شعبة الخطابة للتبليغ الحسيني تقيم ورشة بعنوان (مهارات الخطيب في التأثير والإقناع) في بغداد

سماحة السيد الصافي يؤكد توسيع الخدمات الطبية المقدمة للزائرين والاستعداد للزيارات المليونية

المزيد

الآخبار الصحية

المشمش المجفف.. كنز صحي للقلب والعظام مع تحذيرات مهمة

خطر خفي في أكياس الشاي يثير مخاوف صحية

نظام غذائي شائع يظهر نتائج واعدة لمرضى السكري

تقنية نانوية روسية تشخص النوبة القلبية خلال 6 دقائق فقط

المزيد

الآخبار التكنلوجية

دراسة جديدة تكشف التركيب الحقيقي لكوكب الأرض

علماء يكتشفون انخفاض صلابة الألماس عند تحويله إلى مقياس نانوي

ثورة في علاج الصمم.. علاج جيني يحقق نتائج استثنائية في استعادة السمع

منهج جديد باستخدام الساعات الذرية يعيد طرح سؤال: ما طبيعة الزمن؟

المزيد

مواضيع ذات صلة

Electrophoretic Techniques : Support Media and Buffers

Principles of Liquid Chromatography

Preliminary Purification Steps

Cell Disruption and Production of Initial Crude Extract

Determination of Protein Concentrations

Molecular Biotechnology and Applications

The Biology of Restriction Enzymes

The Isolation of DNA

MODERN BIOTECHNOLOGY

ANCIENT BIOTECHNOLOGY

DEFINITIONS OF BIOTECHNOLOGY

Future Perspectives of Biofuels and Biotechnology