iThei mdcdaelcinfd o c elllllrlllll tiThcl elThhlThscd mmshblkdho c dhpThyroid peroxidase antibodies (TPOAb) are formed in response to this
thyroid injury. These antibodies activate the immune system, which leads
to an all-out search and destroy mission on the enemy.
The immune system then launches an attack to try to clear the body of the
invader; unfortunately, in this case, the immune cells target healthy thyroid
tissue instead.
Hashimoto’s has been classified as a type IV hypersensitivity, which is
called a delayed type hypersensitivity (“self-allergy”). Unlike other types
of immune reactions, the damage to the thyroid tissue is not antibody-
mediated; instead, the antibodies “mark” the thyroid cells, and then
antigen-specific cytoxic T-lymphocytes (lymph cells) attack the targeted
thyroid cells.5,6
Lymphocytes (also known as white blood cells) enter the thyroid and begin
to destroy it, causing scarring, which leads to a decreased ability to produce
thyroid hormones.
The production of TPO antibodies perpetuates the attack on the thyroid
whenever TPO is expressed. These antibodies keep forming as long as
TPO is around, and this eventually leads to so much scarring to the thy-
roid tissues that the thyroid can no longer produce adequate hormone.
More than 90 percent of people with Hashimoto’s have thyroid peroxi-
dase antibodies.^6
Additionally, antibodies may also be formed to thyroglobulin (Tg),
an intermediary protein in the thyroid hormone production pathway.
Iodine attaches to tyrosine residues in thyroglobulin, forming a new mol-
ecule. In the presence of iodine, thyroglobulin becomes more visible to
the immune system. It has even been suggested that excess iodine may
create “mutant” thyroglobulin molecules that may be especially targeted
by immune cells. Thyroglobulin also acts as a storage molecule for thy-
roid hormones, so iodine consumption may actually trigger a thyrotoxic
episode of hyperthyroidism that can cause palpitations, anxiety, and agi-
tation due to destruction of the storage protein and spillover of the stored
thyroid hormones. About 80 percent of people with Hashimoto’s have
thyroglobulin antibodies (TgAb).^6
Collectively, all antibodies directed against thyroid processes are known
as microsomal antibodies, but this term is also sometimes used to re-
fer to TPOAb specifically when discussing different types of antibodies.
Microsomal antibodies are classified as immunoglobulin G (IgG) types
of antibodies, which are responsible for fighting infections as well as for
delayed types of food sensitivities.