Our Border Patrol

The so-called “immune system” is actually a border patrol.

Physicians and medical researchers have used the term “immune system” to identify the cellular and protein elements that fight off infecting organisms.  However, this system is only called into service when there has been a breach in the integument — the skin and other epithelial linings — that allows microbes to enter the interstitium in the first place.  It is a paradigm shift in medicine to consider this so-called “immune system” to actually function as a border patrol.  Like the border patrol, our immune system doesn’t respond at all unless there has been a defect in the integument allowing for microbial invasion.

Consider the strategic locations of our immunocytes:

• Waldeyer’s ring: A large accumulation of lymphocytes and other immunologic cells that comprise the tonsils and adenoids at the back of the nose and mouth.  This serves as a protective area for any potential invaders that enter our bodies by breathing or swallowing them. 
• Lamina propria: This layer of the small intestine lies just under the epithelial lining and is home to huge number of immunocytes.  The intestinal lumen on the other side of the epithelium is full of bacteria, so that any break in the single-cell-layer thin epithelium could spell disaster without border patrol lined up to engulf the invaders.
• Peyer’s patches: An accumulation of lymphocytic tissue in the terminal ileum, where the concentration of bacteria are especially high.
• Kuppfer cells: Macrophages in the liver, positioned to deal with any microbes that entered the portal venous system through epithelial defects.
• Lymph nodes: Accumulation of lymphoid tissues draining lymphatic ducts that bring interstitial fluid from integumentary regions.

It truly appears that our immune system is positioned around potential integumentary breaches.  In contrast, it is interesting to note that our most vital organs, such as the brain or the heart, don’t have any lymph nodes or other immunologic structures.  Given our primitive heritage, there were never any infections that were able to get that deep in a surviving patient.  Such a need would only be necessary with modern critical care.