A new, previously unknown mechanism of immunity has been identified by researchers at Children's Hospital Boston and Harvard School of Public Health (HSPH). This discovery suggests that there may be a better way to protect vulnerable children and adults against Streptococcus pneumoniae (pneumococcal) infection.
According to researchers, the findings may help in the development of novel pneumococcal vaccines.
Pneumococcus causes serious infections in children and the elderly, including pneumonia and meningitis (inflammation of the brain).
Richard Malley, MD, of Children's Division of Infectious Diseases, and Marc Lipsitch, D. Phil., of HSPH have been studying how natural immunity against pneumococcus develops, and have shown that in addition to antibodies, T-cells can provide broad protection against this pathogen.
In this new study, the researchers identify the specific protective T-cells - so-called TH17 cells - and show that they protect against infection by releasing IL-17, a protein that enables human blood cells to kill pneumococcus in the nose more efficiently.
This is significant, since colonizing a person's nose is the first necessary step of infection.
Researchers had known that children, as they get older, carry pneumococcus in the nose for shorter periods of time and have less risk of disease, but it hadn't been known how this resistance develops.
The researchers now show that adults and older children, but not newborn babies, have TH17 cells that target pneumococci, suggesting that exposure to pneumococcus normally leads to production of these cells.
In mice, they show directly that exposure to pneumococcus triggers the development of these T cells and shortens the duration of nasal carriage of the pathogen.
The researchers also describe an efficient way of measuring TH17 cells, which could help determine whether a new vaccine is rallying an effective response.
"We are now evaluating vaccine candidates and changing them so they not only induce antibodies, but also induce this specific type of immunity. A vaccine that induces both protective antibodies and T-cell immunity to pneumococcus may be a very effective way to protect against this potentially devastating disease," said Malley.
The study is published in the open-access journal PLoS Pathogens on September 19.