Flu vaccines protect people by activating white blood cells that, in turn, boost the development of antibodies to the flu, a new study suggests.
The finding may lead to more effective vaccines -- especially for people whose immune system isn't robust enough to fully protect them from the flu, such as the elderly, the study authors said.
"Most importantly, we found that the appearance of these cells in blood correlated with the development of protective antibodies against flu. Therefore, these cells appear to be very important for the successful flu vaccination," he said.
The failure of older people to generate a protective antibody response after a flu vaccine might be associated with the failure to produce these CD4 T cells, Ueno said.
This year, for example, the flu vaccine was only 9 percent effective in older people against the dominant H3N2 strain, according to the U.S. Centers for Disease Control and Prevention. Finding ways to boost a vaccine's effectiveness is especially important for seniors, who are at higher risk of complications from the flu and are more likely to die from them.
One way to help high-risk people might be to identify those whose immune response is likely to be insufficient to fully protect them from the flu, the researchers said.
"You could potentially screen people for their antibody response -- particularly young children and the elderly," said Andrea Sant, a professor with the department of microbiology and immunology at the University of Rochester, in Rochester, N.Y.
This screening could also be important during flu pandemics, said Sant, who was not involved with the study. "You could find out if a dose is sufficient to protect people and those who might need a boost," she added.
Sant said using these CD4 T cells might also be a way of making vaccines more effective.
"Theoretically, you could fine-tune vaccines so they could allow people to have more of these cells in their body when they get a vaccine, either by adding them to a vaccine or administering them before a vaccination," she explained.
The new study was published online March 13 in the journal Science Translational Medicine.
Looking at small groups of children and adults, the researchers found a special type of CD4 T cells that appear after receiving a flu shot. Specifically, these CD4 T cells have three components -- called CXCR5, CXCR3 and ICOS -- that are the key to boosting the immune response to a flu vaccine, the study authors reported.
So, in older people who have a lot of these memory cells, boosting CD4 T cells might help memory cells to respond and launch an immune defense, the investigators suggested.
"Therefore, it would be very beneficial and important to understand the mechanisms by which these cells develop in humans. These studies might lead to the development of more effective vaccines for flu and other diseases," Ueno said.
Another infectious diseases expert, Dr. Marc Siegel, clinical associate professor at NYU Langone Medical Center in New York City, added, "If you could boost this process you could boost immunity, and this could help the elderly who have an impaired immune response."