GenPath Chapter 6 Flashcards
Where are toll-like receptors found?
Plasma membrane and endosomal vesicles
All TLRs signal by a common pathway that culminates in teh activation of two sets of transcription factors….
- NF-kB (stimulates the synthesis and secretion of cytokines and the expression of adhesion molecules)
- Interferon regulatory factors (IRFs) that stimulate the production of the antiviral cytokines, type I interferons
What are NOD-like receptors?
Cytosolic receptors named after the founding member NOD-2
Recognize a wide variety of substances (products released from necrotic/damaged cells such as uric acid, ATP, loss of intracellular K ions, some microbial products)
NLRs signal via a cytosolic multiprotein complex called the inflammasome
WHat is the inflammasome?
It is a multiprotein complex in the cytosol triggered by signaling from NOD-like receptors
–> activates capase-1 that cleaves a precursor form of the cytokine interleukin-1 (IL-1) to generate the biologically active form
recognition of urate crystals by a class of NLRs underlies the inflammation associated with gout
Function of NK cells?
To recognize and destroy severely stressed/abnormal cells (e.g. virus-infected cells and tumor cells)
…make up 5-10% of peripheral blood lymphocytes
What markers to NK cells express?
CD16 (receptor for IgG Fc tails that confers on NK cells the ability to lyse IgG-coated target cells)
Activating/inhibitory receptors of NK cells?
Inhibitory receptors recognize MHC class I molecules (expressed on all healthy cells); these inhibitory receptors prevent the NK cells from killing normal cells
Virus/neoplastic transformation reduce the expression of class I MHC molecules –> NK cells engage tehse abnormal cells and the infected or tumor cell is killed
Which cytokines to NK cells secrete?
IFN-gamma
….which activated macrophages to destroy ingested microbes, and thus NK cells provide an early defense against intracellular microbial infections
Which cytokines regulate NK cell activity?
IL-2
IL-15
IL-12
- *IL2 and IL15 stimulate proliferation of NK cells**
- *IL-12 activates the killing of target cells and the secretion of IFN-gamma**
What generates antigen receptor diversity?
Somatic recombination of the genes that enode antigen receptors
Which enzyme mediates recombination in lymphocytes (for receptors)
RAG1 and RAG2 (recombination-activating genes)
inherited defects in RAG proteins result in a failure to generate mature lymphocytes
There are 3 major populations of T cells, name them and their function
- Helper T cells; stimulate B lymphocytes to make antibodies and activate leukocytes (e.g. phagocytosis) to destroy microbes
- Cytotoxic (killer) T cells: kill infected cells
- Regulatory T lymphocytes: limit the immune responses and prevent reactions against self antigens
For T cells to respond, what is the second signal?
1st signal: Recognize antigen MHC complexes, additional signals provided by antigen-presenting cells
2nd signal: CD28
For B cells to respond, what is the second signal?
Signal 1: antigen binding
CD21 is a receptor for complement component that also promotes B-cell activation
What are Langehans cells?
Immature dendritic cells within the epidermis