While researchers have observed for decades that certain vaccines seem to help recipients ward off more than just the target pathogen, only in recent years have they identified possible mechanisms for these bonus benefits. For example, in a study published this year (depicted here), researchers examined immune cells from the blood and bone marrow of healthy adults before and after they received a live tuberculosis vaccine known as bacille Calmette-Guérin, or BCG.
In the bone marrow post-vaccination, genes are expressed that trigger hematopoietic stem and progenitor cells to differentiate into monocytes, neutrophils, and other so-called myeloid cells. In a separate analysis of the effects of BCG in newborns, the researchers found that the vaccine ramped up the number of neutrophils in babies’ blood compared with unvaccinated infants.
Monocytes from the blood displayed epigenetic changes after vaccination that opened chromatin harboring multiple genes involved in driving an inflammatory response, making them more accessible for transcription. Meanwhile, chromatin closed around genes associated with immune tolerance.
When exposed to the fungal pathogen Candida albicans in vitro, immune cells sampled from patients’ blood 90 days after vaccination released more of the cytokine interleukin 1β, which mediates inflammation, than did cells from blood drawn from the same individuals before vaccination.
Read the full story.
Correction (November 13): Incorrect labels of the open and closed chromatin in the graphic have been corrected. The Scientist regrets the error.