commentary ALLERGIES VS. INFECTIONS
BY WESLEY W. STAFFORD, MD The hu- man immune system has the incred- ible capacity to generate a response to any invading organism and in most cases protect its host from an over- whelming 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 interac- tions complex. These include geneti- cally hard-coded innate components that can kill invading organisms al- most on contact and the adaptive com- ponents 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 im-
mune 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 glu- ten-sensitive enteropathy and allergy.
Most of our offspring are delivered
into almost sterile hospital environ- ments. 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 de- lay in the initial exposure to the polio- virus beyond early infancy, when pro- tective 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. Stud- ies have demonstrated that the more bacteria we are exposed to in our envi- ronment during infancy, the less likely we are to develop allergies. Early ex- posure to bacteria programs our im- mune system to respond with a “type 1” reaction, driving the processes that eradicate infections and produce im-
munity. In the absence of that stimu- lation, 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 im-
mune 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 aller- gies. Children with frequent expo- sures to parasites in rural Africa have a significantly reduced incidence of upper respiratory allergies and asth- ma compared with children from the same tribes who live in the city. Our immune system 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. Q
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.
The components of the immune system are diverse and their interactions complex.
February 2017 TEXAS MEDICINE 19
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