Immune Imprinting

Immune imprinting is a tendency of the body to repeat its immune response based on the first variant it encountered — through infection or vaccination — when it comes across a newer or slightly different variant of the same pathogen.The immune system responds more strongly to the strain of a virus that it first met, weakening response to other strains.

While many of us will be able to stage an immune response to SARS-CoV-2 that we would not have been able to 2 years or even 1 year ago, the individual response may vary considerably between people, depending on the nature of previous exposure. This phenomenon is known as immune imprinting

Imprinting was first observed in 1947 by Jonas Salk and Thomas Francis, the developers of the first flu vaccine, together with another scientist, Joseph Quilligan1. They found that people who had previously had flu, and were then vaccinated against the current circulating strain, produced antibodies against the first strain they had encountered. Francis gave the phenomenon the tongue-in-cheek name ‘original antigenic sin’, although today most researchers prefer to call it imprinting.

Mechanism of Imprinting

Imprinting equips the immune system with a memory of an invader that helps it prepare to do battle again. The key players are memory B cells, which are generated in lymph nodes during the body’s first exposure to a virus. These cells then keep watch in the bloodstream for the same foe, ready to develop into plasma cells that then churn out antibodies. The snag comes when the immune system encounters a similar, but not identical, strain of a virus. In this case, rather than generate new, or ‘naive’, B cells to produce tailored antibodies, the memory-B-cell response kicks in. This often leads to the production of antibodies that bind to features found in both the old and new strains, known as cross-reactive antibodies.

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