February 09, 2013

How Allergy Progresses to Chronic Disease

I wrote about all the ills that potentially emerge for our companions in The Middle Aged Dog as though they were acceptable. "Getting old." Aches. Pains. Constant illness. There's something fatalistic in this - as if progressive degenerative disease were natural. It is anything but.

Once we remove traumatic injury and congenital birth abnormality, chronic disease is the consequence of lifetime patterns of unnatural cause effecting pathological change at the cellular level. Persistent insults to the immune system go unaddressed, uncorrected and unabated. The continuous call on our healthy immune system for an ever-more sophisticated response to maintain balance eventually exhausts it. On this continuum, acute illness progresses to chronic disease.

Eczema in the infant becomes asthma in the adult. Low blood sugar in the child becomes adult onset diabetes. Constant stress becomes high blood pressure begets heart disease.

Perhaps looking at only one of these will help to clarify how this occurs.

News from Washington University St Louis tells us that doctors and scientists have long looked for the missing link between severe skin rash and asthma.
Fifty percent to 70 percent of children with severe atopic dermatitis go on to develop asthma, studies show. By comparison, the rate of asthma incidence among the general population is only about 9 percent in children and 7 percent in adults. Seventeen percent of U.S. children suffer from atopic dermatitis, although not all cases are considered severe.
Is this the effect of an immune system disorder that causes an overreaction that affects the skin and airways? Or do these infants begin with defective skin and airways that trigger an excessive immune response?

Research scientists at Washington University of St. Louis uncovered what might be the key. Their findings, published May 19, 2009, in Public Library of Science Biology, show that a substance secreted by damaged skin circulates through the body and triggers asthmatic symptoms in allergen-exposed laboratory mice. 
The cells in damaged skin can secrete TSLP (thymic stromal lymphopoietin), a compound capable of eliciting a powerful immune response. And because the skin is so effective in secreting TSLP into the blood system, the substance travels throughout the body. When it reaches the lungs, it triggers the hypersensitivity characteristic of asthma - labored breathing, mucous secretion, airway muscle contraction, invasion by white blood cells and conversion of lung cells from one type to another. 
 Additional experiments showed that mice that had normal skin but were engineered to overproduce TSLP also developed the asthma-like symptoms. 
In effect, the skin acts as a signaling organ which responds to assault by releasing a substance that sets off inflammation in the lungs - TSLP.

It's as though the invasion of foreign matter, i.e., virus, bacteria or toxin, sets off a fire alarm. The body is perfectly calibrated to put out the fire. It produces symptoms to extinguish it - heat, swelling, redness. When the invasion persists, the body sets off a more general alarm. Inflammation spreads to other organs, in this case the lungs which produce a cough.

Allergy becomes eczema begets asthma.

Is there no turning back from chronic disease?

Of course.

Millions of people are successfully reversing the course of heart disease and adult onset diabetes by changing diet, staying active and curtailing the use of alcohol and tobacco.

Like the Henny Youngman joke:

Patient: "Doctor my arm hurts when I move it like this."

Doctor: "Stop moving it like that."

If only it were that simple for dogs and cats.
*Skin-Derived TSLP Triggers Progression from Epidermal-Barrier Defects to Asthma. Shadmehr Demehri, Mitsuru Morimoto, Michael J. Holtzman, Raphael Kopan

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