such as bacteria, viruses, fungi and parasites, you are said to have good immunity. Be thankful because there are some of us born with greatly diminished immune ability; or even born without any immunity. Anyone in this category is said to be immunocompromised. This threatening condition makes one extremely vulnerable to invasion by pathogens (an infectious agent that causes disease or illness to its host). The great majority of healthy persons with a well-functioning immune system will have no difficulty neutralizing invading pathogens before they can cause disease, but those whose immune system is compromised may fall victim to the invading pathogen’s effects—including death.
Again, in a book with the title CHALLENGING DIAGNOSES, why do I start with the subject of immunity? Because, as it turns out, most challenging diagnoses patients—the bane of primary care physicians and patients—are those who have developed an illness brought about by a malfunctioning immune system. So, if the readers are to have any hope of understanding what may be ailing them, then they must have a basic understanding of the mechanism that is causing their condition and their physician’s frustration in making what is often a very difficult diagnosis to establish. That is why this book must start with a treatise on the immune system
An understanding about the mechanism involved in the etiology of a puzzling illness, and often a chronic one at that, is crucial for any patient to be able to understand, accept and learn to live within its context. And I stress again: in the treatment of these unusual diseases, there is nothing more important than an educated patient working in collaboration with a dedicated physician. It can be a partnership guaranteeing the best possible result.
IMMUNE SYSTEM
With that in mind, we will first discuss the immune system, the story of the body’s defenses; how the body confronts enemies trying to do us harm. This short story will provide a better understanding of the amazing way this life and death struggle takes place. It is a coordinated system combining the beauty of organs, cells, and complicated collections of proteins working in a harmonious manner for the good of the whole. There are various lines of defense used to keep us alive in a world where invisible or visible predators attack us minute by minute. Besides the foreign substances that can invade us as mentioned above (bacteria viruses, fungi and parasites), we must also include pollen, cancer cells, and internal body cell changes arising spontaneously; the pollen invading us from the outside, the cancer cells invading us from within, the internal body changes arising spontaneously—now all considered foreign and subject to an all-out assault by the immune system.
Getting right down to the details of the immune response, let me advise that the principle mechanism of our specific immune response is carried out by two members of the white blood cell team known as T lymphocytes and B lymphocytes. These two types of white blood cells circulate in our blood stream and position themselves in body tissues by the billions. Their job is to:
•Identify body cells (self) that have changed, thus the lymphocytes do not identify them as belonging to the body, but rather view them as non-self—and attack.
•Identify invaders of the body that certainly do not belong (non-self)—and attack.
In other words, lymphocytes differentiate self from non-self—and anything non-self is eliminated (killed). How do they do this?
All body cells carry distinctive molecules (epitopes) on their surfaces that identify it as self. Our specific immune cells, (lymphocytes), recognizing this self-marker, coexist in a peaceful state known as self-tolerance. Failure to recognize this body self-marker as self, launches a vigorous attack by lymphocytes. What are these immune cells (B cells, T cells)?
Before we get into this very specific line of defense where B cells and T cells attack specific invaders, understand that there is also a mechanism constituting a first line of defense categorized as nonspecific body defenses because they are not programmed to zero in on specific targets like our lymphocytes do, but rather “kill ‘em all.”
As this non-specific line of defense is different from the B and T cells, I have placed them in an appendix so as not to disrupt the story of the specific line of defense. The reader has the choice to read it now or save it for after completing the book. (SEE APPENDIX 1
The red bone marrow is where all blood cells are manufactured including the B cells or B lymphocytes, and T cells or T lymphocytes constituting the specific line of defense. The thymus gland is responsible for putting the final touches on the T cells, producing functioning T cells, or T lymphocytes. Again, these B and T cells are the lymphocytes that are responsible for the specific immune responses.
The red bone marrow where B cells and T cells are produced is also the site of production for all the other cellular elements of the blood including:
1.Red blood cells
2.All the other various types of white blood cells (4) besides the B&T lymphocytes.
3.Blood platelets—important in blood coagulation.
Red bone marrow in adults is located in flat bones (sternum) and in the epiphysis (the end of long bones).
Within the red bone marrow is a stem cell known as a hemocytoblast. Hemo, from the Greek haima (blood), cyto (cells), blast, from the Greek blastos, sprout. This precursor stem cell evolves (sprouts) into two other cells:
•lymphoid stem cell that forms B & T lymphocytes.
•myeloid stem cell that forms the red blood cell, the platelets, and four different white blood cells, the basophil, the eosinophil, the neutrophil, and the monocyte.
These white cells arising from the myeloid stem cell precursors are called leucocytes or white blood cells (from the Greek, leuco white). The latter four are involved in the non-specific system of defense. Again, SEE APPENDIX ONE.
1.The basophil is the rarest of the white blood cells. Filled with histamine granules, it dilates blood vessels and makes them more permeable. In addition, it is one of the agents responsible for attracting other white blood cells to action.
2.The eosinophils increase in number and rally to the cause during infection by parasites, and in response to allergens (any substance that can cause an allergy).
3.The neutrophils are actively involved in phagocytosis (ingesting and digesting bacteria). They have a ravenous appetite for invading bacteria.
4.The monocytes are the largest of all the white blood cells and they change into macrophages when they migrate into tissues from the blood stream. Macrophages have an appetite for bacteria that can cause long standing chronic infections such as tuberculosis.
SPECIFIC IMMUNITY
Let us define immunity again: the body’s ability to defend against specific invaders (viruses, bacteria, toxins, parasites).
This is a very complex subject, the details of which could probably occupy ten volumes. I am going to discuss it, if for no other reason than to acquaint you with the complexity that has evolved in the last sixty years from very little knowledge of the subject of immunity to the great detail and understanding of today.
An antigen is a foreign substance that invokes an immune response. The ability of the body to recognize a foreign molecule (antigen) also means that the body can recognize self from non-self and can memorize. This means that the next time the foreign invader returns, the body will be able to launch an immediate and vigorous response because they have prepared themselves in greater volume of numbers to be ready for another onslaught by the same invader.
