The yellow fever vaccination using the live-attenuated YF17D vaccine is one of the most effective immunizations available. A single dose provides long-lasting protection against the disease.

Due to the strength and long-lasting nature of the immune response it triggers, this vaccine serves as an excellent model for studying effective immune defense mechanisms against viral infections. However, it is still not fully understood how exactly this vaccine elicits such an exceptionally strong immune response.

A team led by immunology professor Anne Krug at LMU’s Biomedical Center (BMC) in collaboration with Simon Rothenfußer, professor at LMU University Hospital, has investigated how specific immune cells—namely dendritic cells (DCs) and monocytes—respond to the vaccine.

To this end, various DC and monocyte cell types were analyzed in the blood of over 200 healthy adults before and after vaccination. Following vaccination, many of these immune cells showed typical activation by so-called interferons—messenger molecules that play a key role in the body’s defense against viruses.

A particularly striking finding was the cell surface molecule SIGLEC-1, which became more prominent on certain cell types within one week of vaccination and was associated with the rapid formation of protective antibodies against the yellow fever virus. The study is published in the Proceedings of the National Academy of Sciences.

“Our study provides new insights into how the immune system responds to a highly effective viral vaccine,” says Krug. “These findings could support the development of new vaccines that offer rapid protection, for example in the context of emerging epidemics. Additionally, SIGLEC-1 may serve as a useful biomarker in future vaccine studies.”