In lesson 1 we had a nice little chat about the history of vaccines, and in lesson two we continued that conversation by introducing the types of vaccines, what lead to their development, and their uses. Now we are going to shift gears a little and get into a slightly more technical discussion on the immune system. I think it is important for people to understand what immunity looks like from a cellular perspective so they understand what vaccines do when they enter the body. If I can get that point across today, then my mission has been accomplished! So, turn your textbooks to the Chapter 3 and let’s get started!
The immune system is a specialized set of cells in your body that act to protect you against pathogens, which are anything that doesn’t belong inside of you. Our bodies are a perfect incubator for viruses, bacteria, parasites and many unsavory microorganisms that, if left unchecked, would easily kill us. The only thing standing between a blood-borne pathogen and your fragile organ systems is the scrappy street fighter that is your immune system. It fights dirty, and it has a pretty impressive win-loss ratio.
In reality, the skin and mucus membranes are truly the first layer of the immune system. The vast majority of pathogens don’t make it past the outer layer of our bodies. Occasionally one will slip through, typically through breaks in the skin, or by sliding past one of the 7 holes in your head. Once the pathogen has made it inside, it is welcomed by the first members of the cellular immune system: the innate immune cells. Think of these cells like the beat cops, patrolling the streets, watching for any kind of trouble. The notable member of this group is the dendritic cell, a particularly feisty cell that engulfs pathogens and digests them. These cells respond to anything they see that isn’t a part of the host, and aren’t specific for any particular pathogen.
But, if there is one pathogen sitting around, chances are there are many more like it in the same area, and the dendritic cells can’t do all the heavy lifting themselves. This is when they call for some help from the other branch of the cellular immune system: the adaptive immune cells. These cells are specific for one particular pathogen, but function more effectively to eradicate it. The dendritic cells communicate with the helper T cells of the adaptive immune system to indicate what specific pathogen is invading the body, and the adaptive immune system cascade then activates the other B and T cells to fight against it. This process involves the production of antibodies against the pathogen, as well as the increase in the number of cells that can specifically react to it.
The problem with the immune system is that a person who has never been exposed to a disease, polio, for example, will have a very low number of adaptive immune cells that are specific to polio. Without a primed adaptive immune defense, the disease is able to spread through the body and will outrun the pace of the immune system’s ability to fight it. To combat this, we have to prime the immune system, expanding the number of T and B cells that are ready to respond to a disease so that it can’t run rampant through your body totally unchecked.
Vaccines do this by giving the body a chance to respond to a pathogen without the risk of a full infection. It is like giving the football team some time on the practice field before the big game. If they go in totally untrained, without knowing how to play the game, then how can you expect them to win? But if you teach them the fundamentals, make them run drills, and show them how to throw and catch the ball, then they actually stand a chance of winning. And, at least if they don’t win they won’t lose as badly as they would have.
Boosting vaccines also fits into the analogy, because over time your immune system starts to lose some of its training and becomes less competent at fighting specific infections. Booster vaccines are like another practice session, reminding the immune system what it is doing. The initial and booster immunizations result in an immune system that can quickly and efficiently fight off potential infections before they take hold. Chances are that you have been exposed at least once in your life to something you have been vaccinated against, but you wouldn’t know because at the cellular level your immune system dealt with it without telling you.
The key is that you can only tell that your vaccines are working when nothing happens. If you got polio tomorrow, you would know your vaccination wasn’t effective, but seeing as there are very few polio patients these days as compared to 70 years ago we can trust that we did something right. What many people don’t realize is that our immune systems have evolved alongside bacterial and viral infections, adapting to the latest threats. This process, however, takes multiple generations, and the process of natural selection and immune evolution usually involves a lot of dead individuals to weed out those who are not naturally immune. Modern vaccines allow us to circumvent this process and develop a defense against a pathogen in a generation or less (in most cases).
Vaccines work. They work well. Compared to the risks, they are a fantastic way to eliminate many crippling diseases. Chances are, no one who reads this has ever lost their motor function to polio, or had their salivary glands become uncontrollably swollen from mumps. There is an incredibly tiny chance that you have had your entire body covered in a rash from rubella, measles, or smallpox. Just a century ago you could have contracted measles, mumps, rubella, smallpox, polio, tetanus, and a long list of other diseases just by walking into the wrong room or shaking the wrong hand. Think about that next time you try and tell someone that vaccines are too dangerous to be used.
