211248, 211249 ELISA Simulation Introduction The Body\'s Defense System The body

Question

211248, 211249 ELISA Simulation Introduction The Body's Defense System The body possesses several lines of defense against infection by pathogenic organisms. Pathogens are tiny, disease-causing agents including viruses, bacteria, protozoa, molds, and other microorganisms. Pathogens invade the body and multiply; they can cause sickness or even the death of the invaded individual. The body employs three lines of defense to prevent and fight off such dangerous intrusions. The first two defense modes are nonspecific. They include the body's physical barriers and the nonspecific immune system. These defenses function without regard to the type of pathogenic intruder. The third layer of defense is the body's specific immune system. Specific immune responses are tailored to the type of invading pathogen. Specific Immune Response Specific immune responses are triggered by antigen molecules. Antigens include proteins and other molecules produced by pathogens. The key players in the specific immune defense are macrophages, and small white blood cells called B lymphocytes (B cells) and T lymphocytes (T cells). Phagocytic macrophages and dendritic cells break down pathogens and display antigenic fragments from the pathogens on the surface of their cell membranes. B and T lymphocytes circulate dendritic cells the in the blood and lymph. When T cells see displayed antigenic fragments, they stimulate specific B cells to reproduce and generate antibodies designed against the specific structure of the antigern encountered. Thus, the word antigen is derived from the term "antibody generator" Antibodies are a group of serum proteins (also referred to as immunoglobulins) that are found in the bloodstream or bound to cell membranes. These proteins all have the same basic Y-shaped structure, but have different antigen binding sites at their ends. Antigen binding sites are designed to fit the shape of specific antigens. Antibodies bind to antigens like a lock and key, forming antigen-antibody complexes (see Figure 1). Antigen Antibody Figure 1. Antigen-antibody complex When an antibody forms an antigen-antibody complex, generally it marks the invading organism/antigen for destruction or for clearance from the bloodstream by phagocytic cells. This removal is designed to prevent the organism/antigen from infecting the cell. Antigen-antibody complexes also stimulate additional immune responses to aid the body in clearing an infection.

Explanation / Answer

2.ELISA tests indirectly detect infection by assaying patients’ blood serum for antibody molecules designed to target the infectious agent in question.

In indirect Elisa test, first, the well of plastic microtire plates is treated with antigen protein of the infectious agent. Antigen protein binds to the bottom of well by hydrophobic bound, which is then washed with buffer to remove the unbound antigen protein. Afterward, the well is treated with blood from the patient(with suspected antibody), if the antibody against the antigen is present they will form an antigen-antibody complex which is followed by washing the well to remove excess antibody or unbound antibodies.

To detect the antigen-antibody complex, secondary antibody (which can recognize the primary antibody) attached with color changing enzyme is added to the well. The secondary antibody binds to the primary antibody which is then treated with chromogen substrate which undergoes a chemical reaction to change color by the enzyme attached to secondary antigen.

So the color change depicts the presence of specific antibody in the patient's serum and no color change depict the non-infected patient.

3. Antigen-antibody complexes formed in the initial steps of an ELISA are not visible to the unaided eye. Therefore, a colorimetric detection system involving a secondary antibody and chromogen is employed. The secondary antibody, which is conjugated to an enzyme, recognizes and binds to primary antibodies of antigen-antibody complexes, if they are present. Chromogen substrate is then added. If present, the enzyme linked to the secondary antibody changes the color of the chromogen. A color change indicates that the patient has antibodies against the pathogen and has been infected..

4 .Each assay was performed in triplicate to ensure reproducibility of the results.

5. Weak positive results may be an indication that the patient’s blood serum carries few antibodies against the disease-causing agent. The patient’s exposure to the pathogen may be recent and the body may not have launched a full immune response yet. Alternatively, the infection may have occurred long ago, and the level of antibodies in the patient’s bloodstream is declining

6.

Related Questions

Navigate

• Browse (All)
• Browse 2
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.