Views:1 Author:Site Editor Publish Time: 2020-03-30 Origin:Site
When the human body comes into contact with foreign antigens, the earliest antibody produced is IgM (Ig stands for Immunoglobulin / immunoglobulin), but it also needs to be about a week after the body feels the pathogenic stimulus, so it is not as good as nucleic acids in the detection time window Detection comes fast.
IgM is actually a secreted form of B-cell receptor (BCR) on the surface of B lymphocytes. This is a patrol prepared in advance during the maturation of the human body, but it is equivalent to a recruit's egg and has not really seen the enemy. After IgM recognizes the antigen, the B cells that produce these IgM will enter the lymph nodes. Here, they are trained by the help of antigen-presenting cells APC (mainly dendritic cells DC) and helper T lymphocytes that have been analyzed for hostility. The qualitative leap of the enemy's ability, the B cell itself also became aware, and evolved, which is equivalent to the first-level fighter in Civ becoming a sixth-level fighter. The result of evolution is the differentiation from B cells to plasma cells, which can be secreted in large quantities. Antibodies, and the affinity of these antibodies is much higher than IgM, this is IgG. IgG exists in the body for a long time, and some can exist for decades. However, IgM only appears when the pathogen first arrives and lasts about one week. Therefore, IgM can be used to reflect whether the body is in an acute infection state.
After understanding the body's antibody response law, we know that if IgM antibodies against the new coronavirus can be detected in human blood, then clinical diagnosis can be made.
Then the principle of colloidal gold test paper for IgM capture method is well understood.
The layout of the test strips is still the same, except that everything is different--
A blood sample (serum) is dripped on the sample pad. There may be IgM antibodies against the new coronavirus, and the gold-labeled antigen reserved at the binding pad, rather than the gold-labeled antibody. This antigen is a protein of the new coronavirus (recombinantly expressed in vitro). IgM will then bind this antigen and bring the colloidal gold on. The detection line is placed against antibodies against human IgM. In this way, if there is IgM in the blood sample, a portion of the antibody will be intercepted by this antibody. The line does not develop color. So this is the principle of the detection line.
For the quality control line, here are laboratory-made antibodies against the gold-labeled antigen at the binding pad, so regardless of the specific IgM in the sample, as long as the flow medium is added, the gold label at the binding pad is added. Antigens will be captured in this place, that is, the quality control line will definitely show color. Then this quality control is as simple as above, about 15 minutes, you can judge based on the color of the two lines.
After the principle is introduced, the biggest advantage of colloidal gold is fast and convenient.
But the disadvantages are also obvious-the throughput is not high, and the accuracy of the test strip is highly dependent on the specificity of the antibody. If the quality of the antibody is not good, it is easy to have cross-reactions and cause misjudgment. In addition, IgM is produced later than virus replication, so the detection window is not as good as nucleic acid detection.