Thymus Flashcards
what antigen is expressed in acute leukemia?
CD34
what tumor often presents with bence-jones proteinuria?
multiple myeloma- tumor of plasma cells arising from the bone marrow
Horse presents icteric with rapid breathing and increased heart rate
* On PE the horse was depressed with a fever and petechiation of the mucous membranes
* On necropsy: * Icterus
* Splenomegaly
differential?
equine infectious anemia
transmitted by biting flies
diagnosed by coggins!
what does the thymus look like in ruminants and pigs?
has cervical and thoracic lobes
what other species variably have small cervical lobes?
cats and horses
T/F: dogs rarely have cervical lobes on the thymus
false, they do NOT have cervical lobes
T/F: all animals have thoracic lobes of the thymus
true
ventral in horse, pig, dog and dorsal in ruminants
what is the thymus important for?
development of T cells
what does the thymus stroma contain?
epithelial cells, reticular cell specialized fibroblasts), macrophages and dendritic cells
these are the supportive components of the thymus
what does the cortex of the thymus contain?
cortical and medullary epithelial cells- essential for T cell development
these are antigen presenting cells
what are hassell’s corpuscles?
degenerating epithelial cells, but still important for T reg production: dendritic cells mediated T reg production
what is the cell of origin of a thymoma?
thymic epithelial cell
what are the 3 zones of the thymus?
- subcapsular zone: T progenitor cells enter from bone marrow
- cortex: DP T cell recognizes antigen/MHCII or antigen/MHC1, then go to positive selection. T cells that recognize MHCI/self antigen go to NEGATIVE SELECTION
- medulla: 5% of remaining mature T cells leave thymus and are distributed to spleen and lymph nodes
what do T cells recognize that leads them to undergo negative selection?
MHCI/self antigen
how do T cells enter the thymus? how do they leave?
progenitors go from BM to thymus, enter subcapsular zone as DN T cells, then go into cortex as DP T cells, then in medulla as SP T cells, then leave and go to the peripheral and lymphoid tissue
a DP T cell recognizes MHCI/self antigen. does it undergo positive or negative selection?
negative selection
what do DN cells express?
nothing; CD4 and CD8 negative
DN cells become DP cells. what do these DP cells express?
CD4 and CD8 positive
what do single positive cells express?
leave thymus either as single positive cells- express either CD4 or CD8
shouldn’t leave thymus as anything other than a SP cell!
what can cause the thymus to decrease in size?
- involution: normal process, decreases in size after a couple years
- hypoplasia: in animals with fetal disease
- atrophy
- necrosis
why does thymus involution occur?
it occurs following sexual maturity
lymphoid and epithelial components are replaced by adipose and connective tissue
T cells continue to circulate thru splenic and lymph node T zones
antigen-specific T cell expansion occurs with antigen presentation
T cells stick around and have memory: do don’t need to use thymus throughout life
why does thymic hypoplasia occur in neonatal animals?
immunodeficient: small and wimpy thymus
why would the thymus atropy or necrose?
lymphocytolysis or inadequate supply from bone marrow
- heavy metals, radiation, anti-cancer therapy, fungal toxins
- viral disease
what viruses can affect the thymus?
- parvovirus: dogs/cats: injures lymph tissue/necrosis
- canine distemper: injures lymphoid tissue
- feline immunodeficiency virus: injures lymphoid tissue
- equine herpesvirus 1: injures lymphoid tissue
- bovine diarrheal virus: injures lymphoid tissue
- porcine circovirus-2L injury or inflammation of the thymus
