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Ever wonder why some people never seem to get sick, but others get stuck in bed? Now scientists say it might have to do with special immune cells that are more like jail cells — because they put the flu behind bars. This ScienCentral News video has more.
Perfect Attendance
Remember the kids in school who never got sick? And remember how at the end of year the principal called them up under the bright auditorium lights and gave them a certificate for perfect attendance? They seemed like such perfect little stars glowing up there under the lights… Too perfect.
These days the benefits of perfect attendance exist beyond the schoolyard. Lots of companies give their employees special pins, perhaps a luncheon, or even a bonus check if they clock in on time everyday. Who are these people? What makes them so good?
Now scientists at Washington University in St. Louis say what makes these resilient folks so good may be something beyond their own scholarly diligence and professional drive. They believe some people may have more of a gene called CCL5 than others and therefore are better able to fight off different strains of the influenza virus. The gene turns ordinary immune cells into jail cells that lock up the virus and prevent it spreading through the body.
"People who have less CCL5 might be more susceptible to infection than people who have more," says pulmonologist Michael Holtzman, who recently published his work relating to this hypothesis in the journal Nature Medicine.
Holtzman and his colleagues developed this idea after studying how flu viruses infect the cells lining our lungs. When a virus gets inside these cells, the cells become infected and begin to express CCL5. Then they commit suicide, or an army of circulating immune cells, called T-cells, kills them. This cell massacre is a programmed process that keeps viruses from replicating, dispersing through the body and making us really sick. "It deprives the virus of a home," says Holtman.
The cells that cleanup all of the "dead and dying debris," as Holtzman refers to it, are a second group of immune cells called macrophages. Unlike most cells, they are able to hold viruses inside their membranes without dying and therefore act as jailors — locking up the virus.
"If the macrophage dies, in contrast to these other cells," Holtman says, "if it dies, then it looses it's ability to clean up the place. And if the place stays dirty in that way, it causes more inflammation and more trouble for the body."
As Holtzman's team reported, they think the CCL5 gene expressed in the early stages of infection is what protects the macrophages from dying. When they genetically engineered mice not to have CCL5 and compared them to mice that had it, the mice that were missing the gene died from viral infections, whereas the mice that had the gene remained healthy. When they did a similar study with human cells, the cells lacking the gene were much more susceptible to viruses and more likely to die than cells that had the gene.
Virus-eating macrophage image: Michael Holtzman
Additional laboratory studies suggest that the expression of CCL5 during an infection may have several simultaneous rolls for macrophages: it may call them into action, it may keep them from killing themselves, and it may shield them from the T-cells. All this combined may mean that people who have more CCL5 are better able to resist the flu virus.
Protecting Against the Flu
Holtzman hopes that now that they have a better understanding of how macrophages survive and clear away viral infections, they may be able to develop cell-based, as opposed to virus-based, vaccines. The idea would be to fortify the cellular response to viruses so that people could get one shot that protects against several different strains of the flu.
He also points out that kind of protection would be long lasting and would mean people wouldn't need a new shot every year. Considering the ability of viruses to mutate and the time it takes to manufacture new vaccines, he says it may be better than having nothing if available vaccines were to become ineffective.
"It's maybe not the ideal vaccine, but something that would be helpful," Thomas says.
Hopefully it will be helpful enough to make those of us with less than perfect attendance become shining stars too.
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