iThei mdcdaelcinfd o c elllllrllll mmthsl mbThkThhpscells, but it is also involved in responses to fungi, protozoans, cancers,
and intracellular bacteria through lymphocytes. Cell-medicated immu-
nity is associated with immune rejection of transplanted organs.
Cell-mediated immunity is an immune response that does not pro-
duce antibodies but instead activates different types of cells, including
phagocytes, natural killer (NK) cells, and antigen-specific cytotoxic
T-lymphocytes, which attack and kill virus-infected cells, cells with in-
tracellular bacteria, and cancer cells. Inadequate Th1 response has been
associated with chronic infections and cancer.
This arm of the immune system produces TNF alpha, interferon (INF)
gamma, IL-2, and IL-12, which stimulate natural killer cells and cyto-
toxic cells and are pro-inflammatory. The Th1 immune response is associ-
ated with inflammation and delayed type hypersensitivity as well as IgG2
antibodies like the ones produced in Hashimoto’s. An increase in Th1
cells has been found in Hashimoto’s, with a prominent increase occurring
in more severe cases.
Certain immune-modulating medications based on the naturally occur-
ring Th1 substances—including interferon (used to treat hepatitis) and
IL-2 (used to treat melanoma)—have been associated with Hashimoto’s
thyroiditis development. These medications/cytokines suppress T regula-
tory cells and shift to the production of Th1 cells.
Th2 Cells
The Th2 pathway is known as humoral-mediated immunity. It is named
this way because it involves extracellular substances, or the substances
found outside of our cells, in body fluids (humorous).
This pathway becomes activated in the presence of parasites (such as
worms), which invade the areas surrounding our cells. The cytokines pro-
duced by this pathway are IL-4, IL-5, IL-1, and IL-13. These cytokines
suppress the production of the Th1 inflammatory cytokines and stimu-
late the production of B cells. The B cells are responsible for the produc-
tion of antibodies to mark the invaders and direct the immune response.
An overactive Th2 system has been implicated in IgE-mediated allergic
reactions such as the very annoying seasonal pollen allergies as well as the
life-threatening anaphylactic reactions to bee stings, shellfish, and nuts.
Th17
Th17 cells have recently been implicated in autoimmune conditions.