What *are* viruses, and how do they work?
With the entire world gripped in a crisis about a virus most of us had never heard of a month ago, Western Today had a conversation with Western's own virologist, Associate Professor of Chemistry Gerry Prody, about viruses, how they work, and how we can all best protect ourselves.
Western Today: Many folks lump viruses and bacteria into one box, because they can both do the same thing - make us feel sick. What are differences between the two?
That’s a great question. They are both too small for us to see, but most bacteria can live and replicate on their own where viruses absolutely rely on a host like us in order to make more copies of themselves. Bacteria are single cell living organisms that can carry out a ton of functions like converting food into energy and responding to changes in the environment. Viruses are just packets of information waiting to find a host so they can make more copies of themselves. They actually take over our own cellular machinery for their own insidious purposes. They are very clever that way. One reason this is particularly important is that antibiotics work against bacteria but have no effects on viruses whatsoever. In fact, the only result of taking antibiotics to try and fight a viral infection is potentially producing more antibiotic resistant bacteria. Are viruses just really what we call obligate parasites like tapeworms
Western Today: Viruses have been explained as "organisms on the edge of life" because they aren't even technically alive. How are they able to make us sick and replicate if they aren't technically "alive?"
Another good question, one that I pose to my students on a regular basis. The simplest viruses consist only of their genetic material, either DNA or RNA, surrounded by a protective shield called a capsid. On their own, they are just packages hanging around waiting to be picked up, if you will. But once they find the right host, they can gain entry into a host cell and co-opt the host cell’s normal operating functions, as I mentioned before, to get their own genes expressed to generate more virus particles that can then leave the cell and infect nearby cells or exit our bodies, like when we cough or sneeze.
Western Today: We hear a lot about new strains of viruses when they appear, from SARS to the novel coronavirus to new strains of flu. How do scientists work to stay ahead of these new strains as they appear?
Oh, boy. That’s another good one. The honest answer is that we do a lot of guessing. Educated guessing, sure. The viruses you mentioned, and HIV as well, all have RNA genomes. These are notorious for being able to change or mutate at very high rates. You never know what they’ll do next. For example, the scientists and health officials responsible for developing our flu vaccines have to choose which strains of flu to include in the vaccine many, many months ahead of flu season. They have to predict what strains will most likely to show up for that next round. And we spend a lot of time getting to know as much as we can about the viruses that are here now. All the knowledge that was gained about the Coronavirus that causes SARS has really helped us move forward with understanding how to deal with COVID19 and what might be good vaccine candidates.
Western Today: The CDC is saying that most people, once exposed to the novel coronavirus, will have a period of one to two weeks before their body begins to create antibodies that allow us to fight back against the virus' attack on our system. What is our body doing in these two weeks to prepare - is it a sort of "antibody boot camp" where the troops are being trained, and if so, how do antibodies "learn"?
This is actually kind of a sophisticated question. The students who just completed my Immunology course took several weeks, if not more, out of the quarter to develop an understanding of these processes!
Some basics: our immune system has two arms, the innate and the humoral systems. The innate system works all the time and includes barriers like skin and mucous, but also stuff inside including cells and cool molecules such as Toll-like receptors. These latter guys should be working to try to destroy the RNA that’s showing up in our cells that isn’t supposed to be there. But the real heavy artillery in the battle against our pathological invaders comes from the humoral system. This branch also has two arms, the humoral arm and the cell-mediated arm. The antibodies you mentioned belong to the humoral system and are created by B cells. These cells are generated in the bone marrow and as they mature, they are programmed to produce a single type of antibody which they proudly display on their cell surface. It has the unique ability to recognize something foreign called an antigen. What is this antigen? We don’t know and neither do they!
In other words, these unique antibodies are generated BEFORE any exposure to the antigen occurs. Isn’t that weird? But that’s how it works. So these young B cells are circulating around waiting to find the right binding partner. When they do, BAM. Stuff starts to happen. Lots of stuff. The cell is triggered to replicate and all the progeny cells will also make that one particular antibody that will bind with the target antigen. Then most of those cells will be triggered to develop into what are called plasma cells which are basically antibody factories that churn out antibodies day and night. It turns out they can also learn how to make better antibodies as they develop.
By the way, the rest of the cells turn into memory cells so that the next time we encounter the same antigen, the lag time to make plasma cells is shorter and the amount of antibodies we can produce in a short time is a lot higher. So, as you can hopefully see, all this takes time and that’s what the lag time is all about.
Western Today: Each virus has what is called its "host range" - the relatively small number of cells it can attack and impact. What is the host range for the novel coronavirus and how can people best protect themselves?
Yes, you’re right. This virus seems to be restricted to the respiratory tract. In order to enter a cell it has to find an entry point or hand to help it inside. That hand is a cell surface protein called ACE2 which stands for Angiotensin I Converting Enzyme 2. That’s a mouthful. But it’s a molecule on the surface of lots of cells, especially on the tongue and other cells like in the nose and lungs. You’ve heard this a lot, but your best protection is to stay home if you can. I know it’s hard. If you must go out, be sure you’re washing your hands often. Soap and water is best by far, but the disinfectant is good if that’s what’s available. Stay six feet away from other people. Try to exercise your mind and body daily.
Gerry Prody has taught at Western since 1984. She received her doctorate in biochemistry from the University of California at Davis in 1981.