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Principles to understand
pentadecacatechol from the leaves makes covalent bonds with keratinocyte proteins, producing modified self that is analogous to viral infection
2-3 days after a second exposure, T cells initiate delayed hypersensitivity reactions. they get there because of increased vascular permeability (due to scratches, say) and generalized inflammation. furthermore, scratching spreads the antigen
macrophages eat derivatized keratinocytes and this causes blisters
IgE is not involved
treatment is suppression of T cells locally or systemically
Type IV immune-mediated tissue damage
immune reactant is T cells
antigen can be soluble or cell-associated
if antigen is soluble, macrophages can ingest it, present it, and be activated by TH1 cells
if antigen is cell-associated, CD8+ T cells will effect a cytotoxic response (normally a virus-killing function)
examples: contact dermatitis, graft rejection
in graft rejection, the graft looks like modified self, just like it does in contact dermatitis
T cell looks at both the alpha helices of the MHC as well as the peptide sitting in groove
positive selection in thymus: T cell taught to recognize self MHC loosely, so there is a good chance it can recognize other MHC of the same species as well (10% of T cells recognize other non-self MHC)
but there is no negative selection for other MHCs, and no negative selection for problems of graft rejection (there is not enough time for evolutionary selection)
so if you have the ability to develop contact dermatitis (killing modified-self cells), you have the ability to reject grafts
rheumatoid arthritis, diabetes mellitus are also examples: combined T cell and antibody response (i.e., type III hypersensitivity responses)
Time course of contact dermatitis
swelling in skin can be as long as 2-3 days after exposure
antigen is injected; TH1 effector cell recognizes antigen
there must have been a prior exposure for there to be TH1 effector cells around
TH1 cells signal release of cytokines from macrophages
this can happen in the absence of any antibody
the long time course differentiates it from other types of responses
Antigen is processed by tissue macrophages and stimulates TH1 cells
some of this antigen drifts up into lymph nodes and TH1 cells get turned on
if you are a severe TH2 type person, you might not have a problem with poison ivy. however, you are probably more susceptible to viral infections
molecules involved are chemokines, cytokines, cytotoxins put out by TH1 cells: IFN-γ, TNF-α, chemokines, IL-3 (stimulates entire marrow), GM-CSF (stimulates a variety of hematopoietic cells, including monocytes and RBCs)
Category: Pathology Notes
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