Cienciaes.com: Antibodies and vaccines: the strength of memory.

2020-11-17 11:59:52

The world has reacted with euphoria to the news that a vaccine against COVID-19 is at the gates. Will it be as effective as they claim? Will it protect us for long? Well, all this will depend on the quantity and quality of the antibody-producing memory lymphocytes that the vaccine manages to generate in each one.

Antibody-producing lymphocytes are called B lymphocytes. We have billions of them, each subtly different from the next. The subtle difference is that each one has a specific antibody molecule on its surface, which has a different external zone. This shape and properties allow it to bind with more or less force to a precise part of the surface of some unknown molecule, an antigen, normally present in one or another microorganism, for example, a virus. If these fit into the antibody on the surface of a B lymphocyte, it is activated and the lymphocyte reproduces, generating thousands and thousands of identical lymphocytes.

From here, two things happen. Either the activated lymphocyte becomes a memory B lymphocyte, or it becomes a cell that produces high amounts of antibodies. These antibodies will bind to the virus molecule and prevent it from binding to others in the body, blocking the infectivity of the virus.

Memory B lymphocytes do not produce large amounts of antibody, but are primed to become antibody-producing lymphocytes much more rapidly if they encounter the antigen a second or more time. Memory B lymphocytes are those that should be preferentially produced in vaccines.

Studies to date have pointed to the possibility that the fate of B lymphocytes depends on the strength with which they bind their antigen, but this was not known for sure. Now, this fact has been confirmed in a series of experiments carried out by a group of researchers from the Rockefeller University in New York.

The researchers find that the B cells that bind the antigen most strongly become antibody-producing cells. In contrast, B cells that bind less strongly to the area of antigen they detect end up becoming predominantly memory B cells. However, a small number of these do still bind antigen with high strength. These will be the first to activate in a second encounter with him.

Activated B lymphocytes have impressive molecular mechanisms capable of producing variants of the initial antibodies. These variants may possess greater binding strength to their antigen. For this reason, in a second encounter with the antigen, the memory cells can undergo a rapid transformation that turns them into highly efficient cells that will also produce very powerful antibodies against the microorganism they detect. Another reason is that memory cells that bind loosely to an initial microorganism can nevertheless bind very strongly to a mutant of that microorganism that we may encounter later. Thus, the memory cells, all together, would somehow anticipate possible mutations in microorganisms and would be prepared to deal with the original and any mutants that may have occurred after a first encounter with it.

This has important implications for vaccine design.

Referencia: Viant et al., Antibody Affinity Shapes the Choice between Memory and Germinal Center B Cell Fates, Cell (2020),

Jorge Laborda, November 15, 2020.

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