Immunity is Life (Part III)


Why do I get infections and how does my body fight them?

Your body is constantly under attack from powerful disease-causing (pathogenic) microbes.  These generally consist of bacteria, viruses and fungi that, if given the chance, can cause infection and death.  Your first layer of defense is your skin and the epithelial tissue that lines your respiratory, gastrointestinal and genitourinary tracts.  If the micro-organisms get past this passive barrier they come up against your immune system.  The immune cells and proteins that first respond to this microbial invasion make up the innate immune system which everyone has at birth.  They determine that an invasion is taking place, raise the alarm, send information to the reserves and try to kill the intruders.  The cells and proteins of the innate immune system have receptors on their surface that can identify about one thousand foreign chemical patterns on the surface of invading microbes.  When activated by using their receptors to lock-on to these foreign chemicals, they use their weapons to try to disable and kill them.  So, although the innate immune system can only identify a limited number of invaders, it’s able to put a large fighting force in the field of combat quickly to begin the defense of your body. 

However, many pathogenic microbes have developed ways of avoiding or defending themselves from the cells and proteins of the innate immune system.  To defend against these more aggressive invaders the cells and proteins of your adaptive immune system must swing into action to provide extra intelligence, firepower and precision accuracy.  As opposed to the innate immune system, which is present at birth, this system develops over time.  It represents the reserves that are called upon within a few days to mount a more specific response.  Clinical experience shows that without the passive barrier of the epithelium, the first responders of the innate immune system or the reserves of the adaptive immune system, our earliest ancestors couldn’t have lived long enough to reproduce because they would have died from infection.            

The cells of the adaptive immune system are called lymphocytes which are produced in the bone marrow.  Some of them migrate to and a mature in the thymus gland (T-cells) and others stay in the bone marrow (B-cells).  They all eventually enter the blood and go into the lymphatics, the tiny vessels that contain the fluid not brought back into the circulation from the capillaries.  From here they move into the lymph nodes and then cycle back into the bloodstream through the veins looking for foreign proteins.  One of the main differences between these cells and the cells of the innate immune system is that rather than having receptors that can detect about a thousand different chemical patterns, they each have about one hundred thousand receptors that can detect only one specific chemical pattern.  It is estimated that altogether, the cells and proteins of the adaptive immune system can detect about ten billion different chemical patterns.  So, in contrast to the cells and proteins of the innate immune system, that have a thousand different receptors which make them able to detect and disable lots of different invaders, each of the cells and proteins of the adaptive immune system are only able to detect and disable a few different invaders.  It’s the first responders of the innate immune system that provide information about the enemy which turns on the right cells and proteins of the adaptive immune system to help in the defense.  

The proteins of the adaptive immune system are called antibodies, also known as gamma globulins or immunoglobulins.  When the cells and proteins of the innate immune system release cytokines to cause inflammation, this allows antibodies to leak out of the blood and onto the battlefield.  They are good at helping other immune cells and proteins identify and kill microbes, neutralize toxins and prevent the further spread of infection.  Here’s how they work.

B-cells each contain about one hundred thousand specific receptors on their cell surface.  When they encounter a foreign protein (antigen) on a microbe that matches their specific receptor they attach to and process it and then place it back on its surface.  When a T-cell that has already been activated by encountering the same antigen attaches to the one on the B-cell it sends cytokines to make the B-cell mature into a plasma cell that produces millions of antibodies.  These antibodies have the same chemical pattern that allows them to attach to the same antigens that activated it and the (helper) T-cell in the first place.

Antibodies are Y-shaped proteins.  The tips of the two branches contain the specific chemical pattern that allows it to attach to a specific antigen on a foreign invader and is called the Fab piece (antigen binding fragment).  Some microbes have defenses that allow them to defy the cells and proteins of the innate immune system.  However, when antibodies become activated by attaching their Fab portions to the specific antigens on the surface of these pathogens their ability to evade and resist these cells is lost.  When this takes place, the base of the antibody, called the Fc piece (constant fragment), becomes activated as well.  The cells of the innate immune system have receptors on their surface that can attach to the activated Fc pieces of the antibodies that have now literally covered these pathogens which now allows them to see and capture them.

There are many other ways that antibodies help the cells and proteins of the innate immune system to get the job of defending the body from life-threatening infection done.  So much so, that clinical experience shows us that there has to be enough antibodies for human life.   

Primary immunodeficiencies are genetic conditions a person is born with which result in a poor immune response to infection.  One example involves defective B-cell function and an almost total absence of antibodies, called agammaglobulinemia.  Infants receive temporary immunity from their mothers by antibodies crossing through the placenta into their bloodstream.  However, after six months, they start to have infections which, if it weren’t for modern medicine, would quickly lead to death.  This shows that even if our earliest ancestors had had all of the other parts of the immune system working properly, without antibodies, they would never have survived.

Finally, it’s important to realize that just like the coagulation cascade, which must turn on only when needed and stay off  or turn off when not, so too, clinical experience shows that when antibodies cause the body to over-react to itself or relatively harmless antigens, this can lead to major debility and even death.  Allergies, such as hay fever and asthma, are caused by certain antibody responses to pollens and sometimes to a bee sting or other chemicals can even cause anaphylactic shock and death.  And when antibodies react inappropriately to normal tissue and turn on the immune system in what is called autoimmune disease, this leads to inflammation, injury and even destruction of different tissues and organs.  Examples of this include rheumatoid arthritis and lupus.  So, it’s vital that not only all of the components of the immune system be present, but that they also be properly controlled as well.      

Three Questions for Mr. Darwin

    1. Where did the information come from to give the cells and proteins of my adaptive immune system the ability to detect about ten billion different chemical patterns?

    2. How did my B-cells become dependent on my helper T-cells to transform into plasma cells capable of producing antibodies and how did intermediate organisms survive without either one of them?

    3. How does my body know how many cells and proteins are needed for its adaptive immune system to work properly so I can stay healthy and not die from infection? 

 


Also see Dr. Glicksman's Series on

"Beyond Irreducible Complexity"

"Exercise Your Wonder"


Howard Glicksman M. D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being.

Comments and questions are welcome.

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