What kind of antigens r used?
There are different types of antigens that can be used in serological tests, depending on the specific test and the target of the immune response being detected. Some commonly used antigens include:
1. Native Antigens: These are antigens in their natural state, derived directly from the source organism or tissue. They can be whole cells, cell extracts, or purified proteins. For example, in the Widal test for typhoid fever, native antigens from Salmonella typhi bacteria are used.
2. Recombinant Antigens: These are antigens produced using recombinant DNA technology. Genes encoding specific proteins or antigens from the target organism are cloned and expressed in a host organism, such as bacteria or yeast. Recombinant antigens are often highly specific and can be produced in large quantities. An example is the recombinant Hepatitis B surface antigen used in serological tests for hepatitis B virus infection.
3. Synthetic Peptides: Synthetic peptides are short chains of amino acids that correspond to specific regions of a protein antigen. They are chemically synthesized in the laboratory and can mimic the immunogenic properties of the native protein. Synthetic peptides are commonly used in enzyme-linked immunosorbent assays (ELISAs) and other serological tests. For example, synthetic peptides derived from the HIV-1 envelope glycoprotein are used in serological assays to detect antibodies against HIV-1.
4. Carbohydrate Antigens: Some antigens consist of carbohydrate molecules or glycoproteins. These antigens are often associated with the cell surface or extracellular components of microorganisms and play a role in interactions with the host immune system. Carbohydrate antigens can be extracted and purified from the source organism or synthesized chemically. For instance, capsular polysaccharides of bacteria like Streptococcus pneumoniae are important carbohydrate antigens used in serological testing.
5. Viral Antigens: Viral antigens are derived from viruses and can be in the form of whole virions, viral proteins, or specific viral components such as envelope glycoproteins or nucleocapsid proteins. Viral antigens are used in serological tests to detect antibodies against viral infections. Examples include influenza virus hemagglutinin or hepatitis C virus core antigen used in serological assays.
6. Tumor Antigens: Tumor antigens are molecules expressed on the surface of tumor cells or released by tumors. They can be used as targets for serological tests to detect cancer or monitor the progression of the disease. Tumor antigens can be specific to particular types of cancer and serve as valuable biomarkers.
The choice of antigen in serological tests depends on various factors, including the target of the immune response, the sensitivity and specificity required, the availability of suitable antigens, and the nature of the serological test being performed.