Commentary — February 2017
Tex Med. 2017;113(2):19.
By Wesley W. Stafford, MD
The human immune system has the incredible capacity to generate a response to any invading organism and in most cases protect its host from an overwhelming infection. To do this, it has to be able to identify the "foreignness" of the myriad different organisms with which we come in contact and to destroy them.
The components of the immune system are diverse and their interactions complex. These include genetically hard-coded innate components that can kill invading organisms almost on contact and the adaptive components that "turn on" the wide array of expanding responses we generate to wipe out infectious organisms and then maintain long-term immunity.
We also know, however, the immune system does not always work to the benefit of the organism it is designed to protect. It can turn on its host and produce the diseases we refer to as autoimmune: lupus, rheumatoid arthritis, thyroid disease, and others. It can also react to substances that are foreign but pose no danger, producing the symptoms of diseases such as gluten-sensitive enteropathy and allergy.
Most of our offspring are delivered into almost sterile hospital environments. After we bring them home, we strive to keep them away from "dirty" places, wrapping them in a cocoon of relative sterility.
There are numerous examples of why this does not always work out well. There is good evidence humans have been exposed to poliovirus for thousands of years, but paralytic polio was a rare occurrence until the 1900s. The epidemics of paralytic polio that occurred in the last century have been blamed on better hygiene in the form of modern plumbing. This led to a delay in the initial exposure to the poliovirus beyond early infancy, when protective maternal antibody could help the infant fight off the disease.
The absence of early stimulation of the immune system is also related to the development of allergy. Studies have demonstrated that the more bacteria we are exposed to in our environment during infancy, the less likely we are to develop allergies. Early exposure to bacteria programs our immune system to respond with a "type 1" reaction, driving the processes that eradicate infections and produce immunity. In the absence of that stimulation, we are prone to generating a "type 2" reaction to the relatively innocuous substances that can cause typical allergic sensitization.
The "type 2" reaction of our immune system is actually designed to fight off parasitic infestation, but in our modern environment it rarely has to perform that task. Similar to what is seen with early bacterial exposures, parasitic infestation also significantly reduces the risk of developing allergies. Children with frequent exposures to parasites in rural Africa have a significantly reduced incidence of upper respiratory allergies and asthma compared with children from the same tribes who live in the city.
Our immune system also needs a little workout during early life, or things tend to go awry. Studies suggest we need to quit thinking that our infants and toddlers need to be brought up in a sterile environment. We need to tell parents to quit panicking when a dog licks their kid's face. In fact, maybe we need to tell parents that before their kids can walk, they should get them a pet. Then they should get those kids and their pets out of their nice clean homes and let them play in the dirt.
Wesley W. Stafford, MD, is board certified in allergy, asthma, immunology, and pediatrics. He is past chair of the TMA Council on Science and Public Health.
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