Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Lymphopoiesis wikipedia , lookup
Immune system wikipedia , lookup
Hospital-acquired infection wikipedia , lookup
Polyclonal B cell response wikipedia , lookup
Adaptive immune system wikipedia , lookup
Hygiene hypothesis wikipedia , lookup
Cancer immunotherapy wikipedia , lookup
Immunosuppressive drug wikipedia , lookup
Adoptive cell transfer wikipedia , lookup
UpFront Parts of the Immune System that Protect Against Infection By Terry O. Harville, MD, PhD LET’S REDEFINE THE term “immunity.” Immunity is commonly referred to in a broad sense to represent the processes of providing protection. In people, though, we tend to think of it in narrow terms, frequently focusing on the adaptive components — T and B lymphocytes. Yet, in reality, protection from infections is a broader process, and our immune system contains components that we may not typically have considered as relevant for immunity. Skin and Mucosal Cells Foremost is our skin, a critical barrier that keeps pathogens out of the body. The outer layers of skin are made from layers of flattened dead cells that are held together, making it a more or less waterproof barrier, impervious to minor trauma. There are numerous sweat glands throughout the skin, and sweat contains chemicals that may have antimicrobial properties. A seemingly unlikely component of immune protection is our urine. The urethra provides an opening for which organisms may enter and cause bladder and, in worse cases, kidney infections. Frequent urination can keep the organisms “flushed” from the urinary tract, preventing infections. Another component is tears, which flush away organisms from the eyes, as well as help defend against organisms in the nose. In the early search for antimicrobial agents, Sir Alexander Fleming, a Scottish bacteriologist, noted that tears would cause bacteria to break apart (lyse). It was found that tears contain digestive enzymes that are capable of digesting the cell walls of bacteria. Saliva, yet another component, is capable of doing the same. Saliva contains many digestive enzymes capable of lysing the cell walls of microorganisms. Therefore, tears and saliva “bathe” our upper respiratory tract with antimicrobial protection. We also have several conduits into or through the body, which may be pathways for pathogenic organisms to invade our bodies. These include the ear canals, Eustachian tubes, nose, tear ducts, mouth, lungs, esophagus, stomach, intestines, anus, bladder and urethra. Like the skin, these conduits are lined with cells, albeit different from the skin, that are collectively known as the mucosa. An interesting concept is that the open areas bounded by these mucosal cell linings are actually “outside the body,” even though we may think of them as “in” the body. In other words, the mucosal cells are like the skin, but they line the otherwise open areas found “inside” the body to protect them from the invasion of organisms, and these cells connect directly to the outside world via the mouth, anus, nose, etc. The mucosal cells do not form the stratified layers of flattened cells like the external skin, but they do have help from specialized cells that secrete mucous. The mucous provides an additional barrier over the cells, making it more difficult for organisms to invade. In the ear canals, a waxy material is produced for the same purpose. When considering the scale of size of the milieu in which microorganisms live, the movement of bacteria in water is comparable to humans swimming through tar. And, mucous adds to this viscosity, further impeding invader organisms. Critical Protective Barriers Clearly, the barrier provided by skin and mucosal cells is a critical component of normal immune system protection. Further, the flow of fluids can help “flush” away microorganisms, and many of the fluids have intrinsic antimicrobial activities. In addition, the secretion of mucous helps to further protect the mucosal cell layers. Although not always recognized for their protective qualities, these immune system components serve as our first line of defense against infections. Next time, we will explore more components of the immune system. TERRY HARVILLE, MD, PhD, is medical director of the Special Immunology Laboratory at the University of Arkansas for Medical Sciences, and a consultant for immunodeficiencies, autoimmunities and transplantation. June-July 2010 www.IGLiving.com IG Living! 9