Immunology - Type IV Hypersensitivity Flashcards
Reactions caused by…
T lymphocyte (sometimes known as T-cell-mediated hypersensitivity)
T cells
mature in the thymus, two types that cause damage to tissues in type IV hypersensitivity = CD8+ T cells aka killer T cells or cytotoxic T cells aka CD4+ T cells/helper T cells, both start off as naive cells because their T cell receptor (TCR) has not yet bound to their target antigen
CD8+ killer T cells
silent killers of the immune system that go after very specific targets, destroy cells directly, can target antigen when they’re presented on MHC class I molecules (present on all nucleated cells in the body so every cell is a potential victim for CD8+ T cells), MHC class I molecules present antigens from inside the cell (this process is particularly important for when cells become infected with viruses or mutated like with cancer (an effector cytotoxic T cell specific to that antigen would use its TCR to bind to the MHC class I molecule which would cause it to release its perforin and granzymes, perforin would perforate the target cell by forming pores, these pores would allow the granzymes to enter into the cell, once inside the granzymes would induce apoptosis)), diseases where this cytotoxic mechanism is involved include tissue destruction in type I diabetes mellitus (CD8+ T cells attack pancreas islet cells) and hashimoto thyroiditis (CD8+ T cells attack thyroid epithelial cells)
CD4+ T cells
locally release cytokines (small proteins that can stimulate or inhibit other cells) to coordinate immune cells around them
Summary
Leads to inflammation and tissue damage via T cells which can be via either CD4+ T helper cells (help coordinate the attack) or CD8+ killer or cytotoxic T cells (directly do the attacking)
Urushiol reaction (poison ivy) - mechanism
quickly makes its way through the epidermis to the dermis where it might combine with small proteins -> might get picked up by a langerhans cell aka dendritic (a type of antigen-presenting immune cell) -> nearest lymph node (the draining lymph node) where it presents the antigen on its surface using a MHC class II molecule -> if a TH cell recognizes the antigen it binds to the MHC class II molecule using its T cell receptor as well as CD4 which is a co-receptor -> CD4+ or helper T cell will also express a CD28 protein which will bind to the B7 protein on the surface of the dendritic cell -> dendritic cell releases interleukin 12 (cytokine, or signaling molecule) that tells the naive CD4+ T cell to mature and differentiate into a type 1 helper T cell (TH1 cell) -> CD4+ T cell no longer consider naive (becomes an effector cell) and able to release the cytokine IL-2, which helps both it and other T cells in the area proliferate as well as interferon gamma which activates phagocytes like macrophages and creates more TH1 cells -> activated macrophages release proinflammatory cytokines like tumor necrosis factor + IL-1 + IL-6 which cause leakiness in the endothelial barriers and allows more immune cells into the area -> local swelling or edema + redness + warmth + systemic symptoms (ie fever), lysosomal enzymes + complement components + reactive oxygen species into the exposed area damage tissue
Urushiol reaction (poison ivy) - type of inflammation
contact dermatitis (inflammation of the skin), can also happen in some people in response to wearing nickel
tuberculin skin test
sometimes called a PPD, a protein from the bacteria Mycobacterium tuberculosis is injected into the skin, if person has been exposed to TB previously they’ll develop a type IV reaction where TB specific TH1 cells will migrate to the injection site and created an inflammatory response that results in the skin getting thick or hard (induration)
A type IV hypersensitivity is also referred to as a ________ hypersensitivity, since it usually takes about ______ hours to recruit ___ _____ to the site of exposure, so these skin reactions usually appear over that time window.
delayed-type, 48-72, TH1 cells
pathophysiology - CD4+
rheumatoid arthritis (TH1 cells cause inflammation in the joints), multiple sclerosis (TH1 cells damage myelin around nerve fibers), and inflammatory bowel disease (TH1 cells cause inflammation in the lining of the intestine)
In addition to TH1 cells, a naive T helper cell (CD4+ T cells) might differentiate into…
a TH17 cell, develop in response to dendritic cells secreting slightly different cytokines (IL-6 and TGF-beta), produce IL-17 (recruiting neutrophils)
_______ ____ test is an example of a type __ hypersensitivity reaction
Tuberculin skin, IV
The primary cellular recruitment in a type IV hypersensitivity reaction involves T-cells and ________
macrophages
The most common type IV hypersensitivity reaction is ______ ________ that occurs after touching poison ivy
contact dermatitis
Type IV hypersensitivity is characterized by _______ symptom onset
delayed
