A second wave
Several days after the innate immune response begins, the body begins a second wave of attacks against the viral invader. This adaptive immune system response is more targeted than the first, methodically destroying cells infected by this specific virus.
But in older bodies, the adaptive response not only takes longer to get into gear, it arrives to find a scene of inflammatory pandemonium, said Amber Mueller, a postdoctoral researcher at Harvard Medical School who co-authored a paper published in May about Covid-19 and aging. Think of firefighters coming to put out a house fire, she said.
“You have a whole neighborhood of pedestrians or bystanders that are just hanging around, screaming their heads off, causing chaos,” she said. “To the point that it makes it harder for the firefighters to find the fire — to find the infection — and then put it out effectively.”
These delays mean that the pathogen has already made many copies of itself by the time the adaptive immune system gets to work and gains a foothold that might not have been available in a younger person. Additionally, older people have fewer fresh T cells, important players in the adaptive response that are trained to hunt down cells infected with a specific pathogen. When everything is working correctly, successful T cells make copies of themselves so that at the height of the infection, the body is swarming with them. Afterward, a few remain to prime us against return attacks from the same virus.
The supply of T cells that hasn’t already been assigned a pathogen dwindles over the decades. Those that remain may not be as good at copying themselves as the cells in younger people. And they may have trouble making the transition to patrolling the body against future attacks, said Dr. Shabnam Salimi, a professor of epidemiology and public health at the University of Maryland School of Medicine who wrote a recent paper about the interaction between aging and Covid-19.
“All these together make the immune system less functional during aging,” Dr. Salimi said.
Research investigating Covid-19 treatments will have to take into account the specific cells and substances that go awry when the immune system ages, and drugs under investigation for fighting aging may be useful against the coronavirus, write Dr. Salimi and her colleague John Hamlyn in their article.
So far, little has been straightforward when it comes to treatments for Covid-19. Since it became clear that the virus sometimes provokes an out-of-control immune response, researchers have been testing whether reducing inflammation might help. Drugs that tamp down the levels of cytokines, like those used for treating rheumatoid arthritis and other autoimmune diseases, have not shown success in fighting the virus. What’s more, chloroquine, which can help inhibit the aging of cells, caused increased mortality in Covid-19 clinical trials.