MadSci Network: Immunology
Query:

Re: Why does hashimato tiroidit not heal?

Date: Tue Mar 3 10:34:15 2009
Posted By: Cenk Sumen, Post-doc/Fellow, Immunology, Memorial Sloan-Kettering Cancer Center
Area of science: Immunology
ID: 1234442329.Im
Message:

A special tip of the hat to Mr. Gurler's query as he is from my place of
birth (Ankara, Turkey) and also since his question pertains to autoimmune
diseases, the ultimate focus of many current projects in T cell function.
Basically, despite having evolved to 
protect the body, the immune system will sometimes attack its own tissues
due to a variety of genetic and environmental factors, causing diverse
diseases such as lupus, multiple sclerosis, Behçet disease, or indeed
Hashimoto's thyroiditis, depending on which organs or tissues are targeted
for self-destruction. Towards the end of this response I will speculate a
bit on why people get these types of diseases at all, but first let's
rewind a century to review the historical context of the discovery of
Hashimoto's thyroiditis. 

Hakaru Hashimoto (1881-1934), a physician from Kyushu, Japan first
published the description of this condition in the medical literature in
1912, referring to it as a "lymphomatous goiter". meaning a swollen neck
due to increased numbers of white blood cells accumulating in the area. A
curious coincidence that may be of particular interest to Mr. Gurler is
that Dr. Hashimoto was born in the same year as Ataturk and likewise died
an untimely death 4 years prior to the founder of Turkey. modernizing the
country, including its medical system. To put this connection in the
context of another autoimmune disease, Istanbul University was established
in place of the Ottoman Dar-ul Fünun in 1933, where Dr. Hulusi Behçet
established the Department of Dermatology. Several years later, he would
submit the first description of Behçet disease, another autoimmune
condition involving inflammation of the blood vessels. Clearly, this decade
was a busy time for medical research and in particular the discovery of
many autoimmune disorders, until the onset of WW2 caused the shift in
medical focus away from research to treating battlefield injuries.

In Hashimoto's disease, lymphocytes (including T cells specific for
self-antigens) invade the thyroid gland (located midway in the neck, i.e..
below the Adam's apple) and destroy the follicles which produce thyroid
hormones such as thyroxine, calcitonin, and triiodothyronine, leading to
"hypothyroidism" (insufficient levels of thyroid hormones). These molecules
regulate key processes in the body such as metabolic rate, protein
synthesis, calcium levels and sensitivity to other hormones. Thus, not
having enough can lead to drastic consequences. Curiously, in the initial
stages of disease there can be marked "hyperthyroidism", possibly due to
antibodies to the hormones cross-linking these messengers and temporarily
increasing their potency. Symptoms may include behavioral maladies such as
depression, fatigue and mania, as well as physiological signs such as
weight gain and elevated heart rate. Hypothyroidism can be treated by
taking hormone supplements, but barring future solutions involving
regenerative medicine (e.g. using stem cells), the patient will have to
continue treatment indefinitely.

Why do people get autoimmune diseases such as Hashimoto's, where healthy
tissues are attacked by the immune system? One theory is that certain
individuals are genetically predisposed to having higher levels of
auto-reactivity, due to their ancestors having survived epidemics by having
more potent immune responses encoded as variations in their genomes. This
is passed on to their progeny in the form of genetic variation, and
maintained in the population in general if it confers an advantage in
surviving childhood infections, for example. Indeed, certain immune-related
genetic factors such as the presence of HLA-DR5 (a class II MHC variant)
and decreased CTLA-4 function expression occur more frequently in
Hashimoto's patients than the overall population. Autoimmune diseases are
also more prevalent in women then men (including Hashimoto's). This is
thought to be due to the fact that females have more potent immune systems,
thus increasing the risk that reactivity to microbes may spill over into
targeting otherwise healthy tissues. The immune system is indeed a
double-edged sword, and one drawback of keeping such dangerous cells in the
body is that they can sometimes turn against their own.



Current Queue | Current Queue for Immunology | Immunology archives

Try the links in the MadSci Library for more information on Immunology.



MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci


MadSci Network, webadmin@madsci.org
© 1995-2006. All rights reserved.