If it is possible to resist an antigen initially, then it is seen that there are several lymphocytes left in the body capable of reacting with that antigen. They can work very quickly if the body is challenged again later with the same antigen. They are called memory cells. The second fast takes less than half the time it takes for lymphocytes to activate and multiply the first time.

dengue

It is because of this pre-preparedness that one can handle intense attacks during this period. For this reason, it takes at least five-six days to detect the IgG and IgM antibodies determined for any serotype of dengue infection for the first time. However, during the second infection, it may come positive from the very first or second day, especially IgG.

It is very good if someone who gets dengue a second time is infected with the same serotype as the first time. Because, the second time he will not suffer much. Pre-existing memory cells will produce a large amount of antibodies and overcome dengue very easily.

For example, someone infected with DENV2 for the first time and then infected with DENV2 the next time. The first time he may have to be hospitalized but the second time he may not even realize the illness. But if the serotype of the second time is different than the first time and the difference between the two infections is more than three months, there is danger! Even in that case, the memory cells produce a lot of antibodies, but they cannot form enough bonds with the dengue virus.

The part of an antibody that binds strongly to its specific antigen is called an epitope. Observations have shown that if antibodies can bind to at least 30 epitopes of the E protein of the dengue virus, the virus can no longer infect any cells. But antibodies specific to one serotype may not capture as many epitopes on the E protein of another serotype.

It has the opposite effect; Because the side of the antibody that binds to the epitope, the opposite side serves as the key to entry into monocytes, macrophages, and dendritic cells. These are dengue virus target cells! Because of the insufficient binding of antibodies to different serotypes, much more virus than would have been able to enter the cell if no antibody had engaged with the dengue virus.

This is called antibody dependent enhancement or ADE for short. Apart from dengue, it is also seen in Zika, yellow fever, HIV etc. viruses. Also, new specific and correct types of lymphocytes are no longer stimulated for the changed serotype. Because there are more memory cells, the protection system does not allow this to prevent 'wasting'. That is, the body becomes stupid.

In such a way that the security system is providing very good protection but in reality the situation is just the opposite. Dengue virus is buzzing inside and outside the cell. To combat them, the cells of the immune system constantly release chemicals called cytokines. It doesn't have much of a virus. But under their influence, the patient loses water from his blood vessels, platelets decrease, hemorrhaging and sometimes even dies.