Alan Frischer, MD, MPH
COVID-19 and Immune System
Why do some people become ill, hospitalized, or even die of COVID-19, while others are asymptomatic, or are not infected at all? Clearly, certain risk factors do make a serious case more likely. They include obesity, diabetes, heart disease, kidney disease, lung disease, and cancer. Certain ethnic groups are at higher risk in this country. However, exciting new research involving T cells may reveal additional significant clues about who becomes sick.
When our immune system kicks in to fight off a germ, it has two major lines of defense. We have physical barriers like skin and mucosal membranes, which physically stop invaders from entry. This is where washing hands, physical distancing, and wearing a mask help. The immune system also includes cells, proteins and chemicals that create inflammation and destroy invading cells. This first part of the immune system is known as the innate immune system.
The second part of our immune system is the adaptive immune system. This takes longer to kick into gear. White blood cells known as B cells produce a unique antibody that can bind to an invading germ, copy itself, and make antibodies; eventually creating an army of neutralizers and stopping the germs from invading host cells.
Several recent studies have found that the antibodies created to stop this particular coronavirus fade away quickly, particularly after a minor case. This is worrisome because if the antibody response doesn’t last long, then one might quickly get infected again, and any future vaccine will not give lasting protection.
But here is the interesting part: As part of our adaptive immune system, helper T cells stimulate B cells to make antibodies. Following an infection, T cells act as memory, and are created by the body to fight future infections from the same invader.
Researchers have found T cells that fight COVID-19 in blood samples that were collected before this pandemic. This has been confirmed in multiple labs across different continents. A recently published summary article in a major immunology journal found that a significant percentage of our population appears to have T cells that recognize parts of COVID-19. Among people who had never been exposed to COVID-19, about half had T-cell reactivity, which would serve as a form of antibody protection.
The theory is that this T cell recognition of parts of COVID-19 may come from past exposure to one of the four known coronaviruses (not including the current novel coronavirus causing this pandemic) that cause the common cold in millions of people every year. Common human coronaviruses infect most of us at some point in our lives. Is it possible that they actually leave a degree of immunity behind, helping some to survive or avoid getting sick from COVID-19? Theoretically, this would mean that reaching herd immunity would be somewhat quicker and easier than we thought. These are preliminary findings, but research continues.
Stay tuned. I salute the brilliant scientists out there who are working hard on understanding this pandemic, and reaching solutions.