The Coronavirus pandemic has a lot of people worried about the dangers of getting infected. It’s easy to get scared, thinking that our bodies have no real defenses against the virus or other microbes like bacteria. That’s not true, however. The human body has a powerful defense system to fight invaders like the virus. Our immune system works hard to keep us healthy – but how does it work, exactly?
It’s not actually that easy for a virus to infect us. First, viruses can only infect us by attaching to specific cells in our bodies – in the case of Coronavirus, those cells are in our respiratory system.
Human bodies have many lines of defense to stop microbes before they even get to the right cells. These include physical barriers like skin, nose hairs (which act as a filter), and mucus that catches and traps microbes before the virus can harm us. We also have chemical barriers in fluids like saliva and stomach acid that can kill microbes before we are infected.
A virus doesn’t simply infect us by touching our bodies – it has to attach to human cells that are compatible with it. Different viruses “dock” with cells with matching receptors. For example, the Ebola virus attaches to cells in the blood vessels and liver, hepatitis attaches to liver cells, and the HIV virus attaches to white blood cells. COVID-19 is compatible with cells in the respiratory system – so you can’t become “infected” unless it gets into your airways. When the virus docks with our cells, it starts reproducing, and we are infected.
The Immune Response
As well as physical and chemical barriers that keep viruses out of our systems, we also have macrophages – a type of immune cell that roams around our body looking for invaders to eat – that stop us from getting sick. When there are too many bacterial or viral cells, and our macrophages can’t cope anymore, they sound the alarm for back up. This is our immune response, when thousands of immune cells charge in to help. Specialized cells called B-cells develop tailored antibodies to fight the infection. It takes some time for the body to design the perfect antibody to match the specific virus – this is when we feel symptoms, like a fever or headache.
Immunity and Antibodies
You may have heard that once a person has contracted and then gotten over COVID-19, they will be “immune” from the virus because they will have antibodies in their system – is this true? Yes and no. The antibodies won’t stay in a person’s system forever, and the amount of time they hang around varies. Even when the antibodies are gone, though, your body is trained to deal with that virus, and it remembers what to do. If you ever catch the same virus again, your body can simply check its records and call in the cells that know how to make that particular antibody – easy!
There’s a catch, though. Just like human cells learn how to kill a certain virus, a virus is always looking for ways to evade our immune cells. That’s how a virus mutates – it changes slightly to try to outsmart our immune system. This creates a different strain of the virus. When faced with a new strain, our old antibodies won’t work anymore, and our bodies have to start the whole process again.
Luckily, the Coronavirus doesn’t pose too much of a problem to the human immune system, so most people who catch it can recover. The main people who need to be careful are those with weakened immune systems or damaged respiratory systems. Science is also looking for ways to treat the virus – but nobody yet knows how much the virus will change, or what treatments would work.