New part of the immune system identified, expected to evolve vaccination.

When a person is exposed to an infection, they are often protected from getting the same infection again.  However, it is still unclear just how the body can fight back so quickly when it encounters an infection it has been previously exposed to through a vaccine or an earlier infection.  Now, a study from researchers at the Garvan Institute of Medical Research identifies the existence of a previously unknown micro-organ within the immune system which they have named Subcapsular Proliferative Foci (SPF).  The team state that the thin, flattened structures, extending over the surface of lymph nodes, are dynamic structures which are not always present, and appear only when needed to fight an infection which the animal has previously been exposed to.  The  opensource study is published in the journal Nature Communications.

Previous studies suggest that memory B cells are formed within the lymph nodes and spleen following a primary infection, and are important in generating an accelerated and more robust antibody-based immune response in the case of re-infection.  However, exactly where and how memory B cells are reactivated to make neutralising antibodies remains unknown.  The current study identifies memory B cells in a subcapsular niche in lymph nodes where, upon reactivation by antigen, they rapidly proliferate and differentiate into antibody-secreting plasma cells in the previously unknown SPF.

The current study uses two-photon microscopy and single-cell RNA sequencing to identify the primary source of the secondary antibody response and show that the seat of B cell memory lies in a previous unknown structure termed the SPF. Results show that memory B cells were clustered at the SPF and were changing into infection-fighting plasma cells, a key step in the fight against infection, due to the fact plasma cells make antibodies to recognise and fend off foreign bodies and protect against disease.

The lab explain that up until now the global medical community has been focussed on making vaccines which can generate memory B cells.  They go on to add that the discovery of this new structure suggests that the focus needs to be on understanding how those memory B cells are reactivated to make plasma cells, so that the process can be streamlined.

The team surmise that they have identified a new part of the immune system, the SPF, where the immune system remembers past infections and vaccinations, and where immune cells gather to mount a rapid response against an infection the body has seen before.  For the future, the researchers state that their new discovery is an important step towards understanding how to make better vaccines.

Source: Garvan Institute of Medical Research


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