Wednesday, November 4, 2009

Before it all Went Wrong: Normal Immune Systems

Image from wikimedia commons

I spend a great deal of time trying to make sense of what my over-active immune system is doing to me. So I spend a considerable amount of time reading medical studies and other in-depth articles aimed at physicians and other health care providers.

I find the scientific literature that defines and discusses autoimmune disease to be complicated and often confusing.

That's because our immune system is complicated and often confusing.

I know that the immune system's responsibilities include recognizing and responding to potentially harmful agents such as bacteria, viruses, and foreign molecules, (see Medline Plus definition here), but the methods by which our immune system accomplishes this seem so complex that when I attempt to make sense of it all, I end up thinking that my name is Alice and that I have fallen down a rabbit hole.........curiouser and curiouser!

Luckily for me, I have some located perfectly sane sources by which I can make some sense of it all. Here's a condensed version of what I have learned. And it doesn't require one to eat part of a mushroom or drink from a mysterious vial of questionable liquid.

We know that in autoimmune disease certain elements of our immune system mis-identify parts of our bodies as foreign, which triggers our immune system to kick into high gear and attack those parts of our bodies and thus we deal with autoimmune disease. But what actually does our immune system do when this happens, either in a normal response or in autoimmune disease? Before one can understand abnormal immune function, it is important to some understanding of normal immune anatomy and physiology.

Our immune system has two basic parts: the innate system, and the adaptive system.

Innate immunity is the body's first line of defense against invaders. It is present at time of birth, and unlike the adaptive system, does not change its response to repeated exposure to a given infection. Once a pathogen, or disease causing agent, penetrates the skin and mucous membrane barrier, specific cells and proteins rapidly move in. These innate responders are not fussy. They will cheerfully attack anything that matches a general pathogen-associated molecular pattern, or PAMP. PAMPs are molecules that are found in certain patterns required for survival of certain viruses and bacteria. Put simply, the cells involved in this attack force look for this molecule pattern and then attack it. When we are born with a normal immune system, our innate system is pre-loaded ready to recognize not just one PAMP, but thousands. Parts of this innate system include:
  • Skin and mucous membranes as an anatomical barrier;
  • Phagocytic cells: specific white blood cells that bind to pathogens and then engulf them. The word phagocyte in greek literally means to "devour cells". Phagocytes include neutrophils, monocytes, and macrophages;
  • White blood cells that cause inflammation: basophils, mast cells, and eosinophils;
  • Natural killer cells that target tumor cells and cells infected by viruses;
  • Specific molecules such as complement proteins and cytokines. 
The innate immune system is responsible for the inflammation, swelling, and fever present in an infection. The innate response does not "learn" or change with repeated infections of the same agent. You can read more about the innate immune system here, and here, and here.

The adaptive immune system is the second of the two basic parts of immunity. Unlike the innate system, the adaptive system is not present at birth, and remembers - or is changed by - repeated infections of the same agent. It is a much more specific response to an infectious agent and takes time to develop. Key players in this system are specialized white blood cells or lymphocytes. This excellent description of lymphocytes and their responsibilities can be found on the Merck Manual site:
"Lymphocytes enable the body to remember antigens and to distinguish self from nonself (foreign). Lymphocytes circulate in the bloodstream and lymphatic system and move into tissues as needed.
The immune system can remember every antigen encountered because, after an encounter, some lymphocytes develop into memory cells. These cells live a long time - for years or even decades. When these cells encounter an antigen for the second time, they recognize it immediately and respond quickly, vigorously, and specifically to that particular antigen. This specific immune response is the reason that people do not contract chickenpox or measles more than once and that vaccination can prevent certain disorders."
There are several flavors of lymphocytes - B cells, which are formed in bone marrow and produce antibodies, and T cells, which are produced in the thymus, and once activated, operate seek and destroy missions for foreign and abnormal cells. Both B and T cells are subdivided into other types of cells with specific functions. To learn more about these specific cells and their complex processes, read more here, here, and here.

Abnormal T cells are thought to be responsible for initiating autoimmune disease when they fail to recognize the body's own tissues as "self", and begin their seek and destroy missions on the body's own organs. You can read more about these errant T cells here.


Veronica said...

Thank you for this article,it makes sense and helps me understand this awful disease. Keep up your excellent work.

Anonymous said...

I was wondering if you can explain triggers such as secondhand smoke. Is it an irritant that sets off our immune systems and then our T cells are free to run around and wreak havoc? I am lucky to have only mild Primary Sjogrens and some mild Raynauds, so I don't have any problem really until it is triggered.

Thank you for this article. I am a musician/artist and most of the medical journals lose me. Thank you for putting it in the terms I can understand!

PS every Sjoggy should move to Seattle. Seattle is a cool midst humidifier all the time. And we have WA Standard Health Questionnaire so you will not be turned away for Health Insurance if you have SS. Yay WA State!