What is revaccination for?
How Immune Cells Hone their Skills
Kirill Stasevich, "Science and Life"
During immunization, we are injected with weakened or killed pathogens of some infectious disease, or their toxins, or some other antigen molecules (for example, proteins or polysaccharide molecules of bacterial cell walls). The vaccine stimulates the immune response, the immune system remembers the "portrait" of the pathogen, and if a real infection enters the body, the immune system will know how to deal with it.
Often, after the first injection of the vaccine, they also do the second one – in this case, they talk about revaccination or reimmunization. Indeed, repeated administration of the antigen makes the immune response stronger, which provides more effective protection against the disease – the vaccine works longer.
However, why this happens, it became clear only now, after the research of Louise and Michael McHeyzer-Williams and their colleagues from the Scripps Institute (USA) - in an article in Nature Immunology Class–switched memory B cells remodel BCRs within secondary germinal centers, they describe how B cells they hone their skills on new portions of antigen (the press release of The New TSRI Study Shows How Immune Cells Hone Their Skills to Fight Disease can be read on the website of The Scripps Research Institute - VM). When a virus, or a bacterium, or an infectious fungus enters the body, B-lymphocytes begin to produce antibodies against them, binding to the pathogen and helping to destroy it. At the same time, part of the B cells is sent to the lymph nodes, where germinative centers are formed - special "stalls" for the storage and reproduction of B lymphocytes.
Memory cells settle in germinative centers, whose task is to recognize even insignificant amounts of the pathogen if it ever appears again. Virus recognition occurs with the help of protein receptors on the surface of lymphocytes. These receptors are the same antibodies in combination with other proteins. Antibodies can be different, and by exposing them from the membrane outside, it is possible to assess how tightly one or another variant of immunoglobulins binds the viral protein and, accordingly, whether such an immunoglobulin is suitable for "mass production". In lymph nodes, B cells are cloned, and each clone receives a random mutation in the receptor. Most mutations turn out to be useless, but there are some among them that enhance the interaction of the receptor with the antigen. If the receptor, and hence the B-cell antibodies, are sufficiently effective at binding a foreign molecule, the B-lymphocyte leaves the germinative center of the lymph node and goes to patrol the body.
What happens when the vaccine is re-administered? It is not limited to one round of training, and with revaccination, secondary germinative centers appear in the lymph nodes, where B-lymphocytes that have been selected after the first administration of the antigen are sent. The next batch of foreign molecules launches a new program of cellular evolution: new clones receive new mutations, and the specificity of antibodies can be altered. That is, the meaning of the second round of tuning is not so much to improve the existing model of immunoglobulins, not so much to make new antibodies bind even more tightly to the same sites of enemy molecules, as to make the response to infection more diverse. That is, on the basis of good antibodies obtained after the first vaccine, new versions are created with somewhat rearranged specificity, which can, roughly speaking, grab the antigen for new places. We can say that the immune system is ahead of the curve here – after all, the variability of viruses and bacteria is great, and the sequences of their molecules change quite quickly. The evolution of B cells triggered by repeated vaccination is a symmetrical response to the evolution of pathogens.
The processes taking place in the secondary germinative centers are very complex, but the complexity here is quite justified, because as a result, the accuracy and diversity of the antibody response can be incorporated into the immune memory at the same time. Well, if we learn more about the processes that occur here, then in the future we will be able to create vaccines that will further improve the memory of B cells, making the immune defense completely impenetrable.
Portal "Eternal youth" http://vechnayamolodost.ru11.02.2015