In previous blog post we looked at the major parts of the immune system, but how do all these parts work together to keep us healthy? Well, it is pretty amazing how the parts of the immune system work together and also quite complex. I will only give a broad overview of how the immune response works in this post.
First, to have an immune response, a foreign substance has to get in the body. The skin and mucous membranes are the first line of defense to keep unwanted things out of the body. Few things readily pass through the skin itself because it is such a good barrier. This is especially true of microorganisms. However a scrape or cut gives things like bacteria and viruses much easier access. So it is important to keep cuts and scrapes clean. Now you don’t have to use antibacterial products or anything fancy to clean a cut or scrape. Just plain old soap and water does a good job of getting rid of most unwanted germs.
The mucous membranes also do a pretty good job of keeping foreign organisms out of the body, but they are more vulnerable because they have to allow for absorption of nutrients and excretion of wastes. The mucous membranes have some extra help from substances like mucous to trap and wash away unwanted invaders. The mucous also contains elements that will help kill bacteria and viruses. Other barriers that work in a similar way include tears, saliva and even stomach acid to prevent foreign invaders from entering the body.
Nevertheless, microorganisms have been dealing with these barrier defenses for a very long time and have adapted and found ways to get through them. These natural barriers are still a considerable part of the immune system and do a good job, but they are only the first defense. Once a foreign invader does manage to get into the body, the body has many ways to deal with the invader.
When the body has been exposed to an organism and had an immune response to it, the body ‘remembers’ and is much better able to handle future exposures to the same organism. This is part of the reason you only get things like chicken pox once. In this post though, I will be focusing on the process the body goes through when it is responding to something that is ‘new’ and is building up immunity to it.
When a foreign invader does get into the body, it goes about trying to multiply and make a new home for itself. The first part of the immune response to encounter the invader is going to be the Complement System. These normally inactive proteins become activated by recognizing general characteristics of the invader. The active proteins can attach to the invader, making it more recognizable to white blood cells and others cause inflammation, which brings white blood cells to the area. Some of the proteins even come together to form a protein complex that can directly attack by poking holes in the cell membrane of the invader.
Inflammation is a very important part of the immune response. While inflammation can be uncomfortable and too much inflammation leads to a number of problems, without it the body could not fight off any infections. Many of the same chemicals that cause inflammation also signal to white blood cells to come to the area and join the fight. Some of the other chemicals released during inflammation also signal the surrounding cells in the tissue to basically increase their defenses against the invader.
The chemical signal is sent out for white blood cells to come and the first white blood cell to respond in force is the neutrophil. The neutrophils come to the area and begin attacking the foreign invader by ‘eating’ them and also releasing chemicals to damage them. The monocytes/macrophages also respond early in the immune response. The macrophages do a much better job of ‘eating’ the invaders. The neutrophils and macrophages do their best to fight and contain the infection but often they need more help.
Now if the invader was specifically a virus, the immune response happens the same way but the natural killer cell has a much more active role. Viruses need to ‘take over’ cells and force them to make more viruses because a virus alone cannot reproduce. The natural killer cells can recognize cells that have been hijacked by viruses and attacks them so that they will not continue to make more viruses.
The neutrophils, monocytes/macrophages, and natural killer cells continue the fight while acquired immunity is getting activated. All the white blood cells mentioned up to this point are part of innate immunity and are not specific to any one invader. While there are billions of white blood cells, there are relatively few T and B cells that will recognize a specific invader. It takes time to find the correct cells but the immune system has an amazing way of doing this. The white blood cells not only circulate throughout the body to have a better chance of ‘meeting their match,’ but there are also certain cells that will actually ‘eat’ bits of the invader and go and show it to the T and B cells that are in the lymph nodes and other lymphoid tissues.
When a T or B cell comes into contact with the invader or part thereof it is coded for, it becomes activated and will begin to divide and create ‘clones’ of itself. Now all the clones will recognize the same thing that activated the original cell, but each type of clone has a different job.
There are two main types of T cells: helper T cells and cytotoxic T cells. The cytotoxic T cell is the ‘attack cell’ after it is activated. The cytotoxic T cell directly attacks foreign invaders by attaching to it and releasing chemicals that damage the invader. The cytotoxic T cell then goes on to find more invaders to attack and kill. The helper T cell is crucial to a powerful immune response. When it becomes activated, it releases chemicals that improves the immune response and helps to activate other white blood cells. In fact, usually a T or B cell has to come in contact with the antigen it is coded for and receive a chemical signal from the T helper cell to become active. To put the importance of T helper cells in perspective, they are most affected by HIV and when the T helper cell numbers become too low you get all the terrible manifestations of AIDS.
The B cell clone that becomes the ‘attack cell’ is called a plasma cell. The plasma cell makes millions of antibodies that are sent through the blood to go to the area of the infection and help in the fight. There are several types of antibodies and they work in slightly different ways. Yet all antibodies basically attach to the surface on the invader and can have a direct effect on the invader or help other white blood cells to recognize and more readily attack the invader. The plasma cell does not have to leave the lymph node or other lymphoid tissue to do its job because the antibodies do the actual attacking. In fact one of the reasons lymph nodes swell while fighting an infection is because the increased number of B cells that become activated and multiply.
One more key clone of both T and B cells is the memory cell. The memory cells are the way the immune system basically ‘remembers’ and gains immunity. The memory cells stick around much longer than any of the other clones and if it comes into contact with the same invader it quickly responds to it. This quick and effective response usually happens without us experiencing any symptoms. We are said to be immune to that invader.
Now with acquired immunity active and the T cells and B cells in the fight, the immune system has the tools necessary to take on almost any invader. However, if the immune system is not functioning at its best, you are more likely to get sick and take longer to fight off an infection. So watch for the next post about 5 things we can do to have a healthier immune system.
