Image by: Amber D. Miller
Vaccines and infectious diseases have been in the media rather frequently of late, especially with the measles outbreak in California and the recent elimination of rubella in the Americas. Most of us have been told that vaccines are beneficial and that they help prevent illness and stop epidemics, but how do they do that? How do vaccines work to stop us from getting sick? To answer that question, we’ll have to dive into one of my favorite topics – immunology, the study of the immune system.
The immune system is one of the most fantastic parts of us. It is the reason why we are able to survive in the world without succumbing to infection every 10 minutes. It is the reason why, when we get sick, we are able to fight off that sickness and return to a healthy state again. The immune system is the police force of our bodies, protecting our insides from dangerous criminals of the outside world.
These criminals may take on many forms. The most common of these criminals (at least in the developed world) are bacteria and viruses (although occasionally we experience attack from fungi or parasites). Bacteria and viruses are both microscopic organisms; they are too small to see without a microscope, and most viruses are too small to even been seen with a microscope.
As I mentioned earlier, the immune system is the police force of our bodies. There are two main branches of the immune system: the innate immune system and the adaptive immune system. The innate immune system is comprised of many different types of white blood cells that act as patrolling police officers. Cells of the innate immune system continually move through the body via blood vessels and lymphatic vessels (specially designed fluid drainage routes). In contrast, the adaptive immune system is made up of white blood cells that remain at the police station (lymph nodes) until called into service by the innate immune system.
When bacteria or viruses invade our bodies, they are recognized first by the patrolling cells of the innate immune system. The immune cells distinguish between invading bacteria or viruses and human cells based on common identifiers present on bacteria or viruses but not present on human cells. It would be like if all criminals wore purple fuzzy hats, and all law-abiding citizens did not; the police would be able to pick out criminals based solely on whether they were wearing a purple fuzzy hat. The same holds true for bacteria and viruses, which often wear different proteins or sugars than those that are found on human cells.
The innate immune system is able to eliminate most invaders without involving the adaptive immune system (officers at police headquarters). These officers have very unique ways of eliminating these threats. Some officers (macrophages) will eat the criminals in a process that is fancily named phagocytosis. Once inside the macrophages, bacteria and viruses will be dissolved in acid pockets called lysosomes. Other officers (neutrophils) will explode near bacteria and viruses, coating the invading criminals with toxic chemicals.
The innate immune system is not able to contain all infections, though. Sometimes, this is because of the number of bacteria or viruses entering the body. More often, though, it is because bacteria and viruses find ways to circumvent the defenses of the innate immune system. In these cases, the adaptive immune system is crucial to ending the infection.
Most cells of the innate immune system can also function as evidence collectors and will present said evidence to the cells of the adaptive immune system stationed at the lymph nodes. Cells that act as evidence collectors are termed “antigen presenting cells.” Antigens are small pieces of sugars or proteins that cover bacteria and viruses. Antigen is evidence that can be used to identify a particular bacteria or virus, similar to a fingerprint. When presented with these fingerprints, the adaptive immune system jumps into action.
There are two main cell types involved in the adaptive immune system: B cells and T cells. B cells could be described as weapon specialists. They create antibodies, which act as homing devices to the antigen of bacteria or viruses. These antibodies circulate through blood vessels and will stick to the appropriate antigen. Antibodies bound to antigen tell the innate immune system to launch an even stronger attack against the invaders.
T cells can perform two main functions. Some T cells will perform more managerial tasks. They give instructions to B cells, other T cells, and other immune system cells. Other T cells are responsible for interrogating our bodies’ cells, searching for viruses and other pathogens which may be hiding within our cells. Remember how bacteria and viruses have their own fingerprints (antigen), so to speak? Our cells also have fingerprints too, but when infected by viruses, our cells will often display viral fingerprints instead of cellular fingerprints. T cells can recognize the difference between own our cellular fingerprints and those of bacteria and viruses. T cells can also force any cell in our body to show its fingerprints. If a T cell finds a cell expressing viral fingerprints, the T cell will kill the infected cell.
To recap everything about the immune system thus far, the innate immune system are the patrolling officers, capable of dealing with some invading criminals on their own. Particularly numerous or sneaky criminals often require the adaptive immune system to eliminate them. Antigen presenting cells present evidence to the adaptive immune system, which can then form homing devices (antibodies produced by B cells) or interrogate our cells searching for virus (T cells).
Now that we’ve discussed how different aspects of the immune system work, how does this apply to vaccines? When you get a vaccine, viral or bacterial antigens are injected into your body. Antigen presenting cells present these antigens to B cells and T cells. Each B cell and T cell recognize one specific antigen, and this recognition allows the cells to perform their duties and to survive for many years. These surviving cells will remain in the lymph nodes and wait for a similar criminal to come again. This process is called immunological memory: the immune system remembers past criminals and mobilizes its officers to eradicate future criminals before they can cause disease. Immunological memory occurs after both illness and vaccination; however, vaccination allows for memory to develop without illness occurring.
Vaccines allow the adaptive immune system to prepare itself for a potential upcoming infection. Thus, if we were ever to encounter said virus or bacteria, our adaptive immune systems would be ready to defend our bodies, and we would avoid dangerous illness.
For more information, check out the following website:
How Stuff Works – The Immune System: