Lecture 20: Transplantation Immunology Flashcards
Differentiate b/w autograft, isografts, allografts, xenografts.
Which one is most susceptible to rapid attack by naturally occuring Abs and complement?
Autograft - from one part to anothe rpart of same individual
Isograft - b/w diff individuals of ID genetic makeup –> ID twins
Allografts - b/w nonidentical members of same species
Xenografs - b/w members of different species
- this type is most susceptible to rapid attack by naturally occuring Abs and complement
What are 3 major conclusions recognizing graft rejection is an immune reaction?
- Graft rejection shows MEMORY and SPECIFICITY = 2 key key features of adaptive immunity
- Mediated by lymphocytes
- Can be mediated by T lymphocytes
- How are HLA Ag expressed?
- Which class are particularly strong barriers to transplantation?
- What are the 3 most important paris of Class II HLA?
- Co-dominantly
- Class I (HLA-A and HLA-B) bc every cell in body expresses Class I
- HLA-DR, HLA-DP and HLA-DQ
* Class II HLA are only on professional APCs
Direct vs Indirect Allorecognition
- Which pathway is: donor APC –> Recipient T cell?
- Which is recipient APC –> Recipient T cell?
- Which pathway is more important for chronic rejection?
- Direct
* TCR on recipient T cells directly recog. the donor MHC mlcls - Indirect
- recipient T cells recognize donor MHC mlcls that were processed by recipient APCs
- donor MHC mlcls are present as peptides in context of recipient Class I and II MHC
- Indirect
What are the 4 variables/key concepts that determine transplant outcome?
- Condition of the allograft
- Donor-host antigenic disparity (want low as possible)
- Strength of host anti-donor response
- Immunosuppressive regimen
Condition of the Allograft:
- What is cold ischemia time?
- When transplanted, the damaged graft tissues release what? This release results in tissue damage.
- Clotting cascade generates what? These then activate which 2 cell types? What is the clinical result of this response?
- Kinin cascade produces what? What are the 3 key clinical responses to this mlcl?
- If these early pro-inflammatory responses go uncontrolled what results?
- Time that the organ is w/o blood and is kept cold, from the time the organ was initially removed from donor to time its transplanted into recipient
* more time –> more ischemia reperfusion damage - mediators
-
Fibrinopepties –> activates mast cells and endothelial cells
* inc. local vascular permeability and neutrophil/MΦ -
Bradykinin
* vasodilation, sm. m contraction, inc. vascular permeability - allograft rejection
During Donor-recipient workup, what is first established?
ABO blood group compatibility
- ABO = barrier to transplantation of solid organ
- Abs to A and B are in ppl w/o these Ags on their RBCs
- ABO matichg is not important for:
- corneal or heart valve transplations
- bone and tendon grafts
- Blood group Ags also expressed on renal and endothelium
For each RBC type, Group A, B, AB, and O, what is their corresponding Ag and Ab?
Group A RBC:
- Ag A
- Anti-B abs
Group B RBC:
- Ag B
- Anti-A abs
Group AB RBC:
- Ag A/B
- no abs
Group O RBC:
- no Ag
- Anti-A/B abs
ABO Compatibility
Patient with A group:
Patient with B group:
Patient w/ AB group:
Patient w/ O group:
A group:
- compatible plasma: A, AB
- compatible washed RBCs: A and O
B group:
- compatible plasma: B and AB
- compatible washed RBCs: B and O
AB group:
- compatible plasma: AB
- compatible washed RBCs: O, A, B, AB
O group:
- compatible plasma: O, A, B, AB
- compatible washed RBCs: O
During donor recipient workup what is used to identify HLAs?
What is a successful transplantaion dependent on?
Tissue Typing
MHC Ags
- this is required due to extreme polymorphorism of HLA (human leukocyte Ag complex)
- What serology test identifies matching of Class I MHC/HLA b/w donor and recipient?
- What is the mechanism behind this (think big picture)?
- What are the primary sources for the lymphocytes?
- Microcytotoxicity
- Complement-dependent serology
- antisera contain Ab’s to HLA Ags
- Abs bind to HLA Ag creating Ag-Ab complex
- activating CLASSICAL complement pathway resulting in lymphocyte lysing
- Lysing is detected by staining the cells
- Spleen and LN
Microcytotoxicity Test main 3 steps are (ie what is added during each step)?
How do you determine if the pt and donor are matches?
- Step 1 = Add Abs
- Step 2 = Add complement
- complement forms pores in cells via MAC
- Step 3 = Add dye
- dye can’t go in unless the MAC has created holes/pores
HLA is ID if both cells show dye accumulation
if dye is only present in donor –> no match–> HLA Ag non-ID
- What is needed to prevent hyperactive Ab-dependent rejection of graft?
- What is this testing for?
- What would the test used to carry this out?
- Cross-matching
- Used to test recipient serum for PREFORMED Abs against donor’s HLAs
* pre-existing Abs due to prev. exposure of pathogen - Microcytotoxicity (modified) test
During microcytotoxicity test for preformed Abs, what result would indicate the donor can be used safely without causing a hyperactive rejection?
If there are no Abs in recipient, the donor cells are are not stained (aka there is no damage to the cell) and they are a good match.
Steps for this test:
- start with donor cells
- add recipient serum
- recipient abs in serum bind to donor cell
- add complement
- add dye
- IF dye accumulates in cell –> preformed Abs are present and would result in hyperactive rejection
- IF no dye in donor cell –> no preformed Abs are present and the potential donor is ID
- Mixed lymphocyte reaction is used in what kind of HLA typing?
- Is this a one or two way rxn?
- Lymphocytes from the donor are called what? What do these serve as?
- Lymphocytes from the recipient are called what?
- What is measured by incorporation of tritated thymidine?
- Class II
- Two way rxn
- Stimulator cells; serve as APC of Class II MCH Ags
* these are initially irradiated to stop their proliferation - Responder cells
* these will be activated by MISMATCHED class II MHC –> then proliferate - Prolieration (ie response)
During MLR what indicates the donor and recipient Class II MHC Ags are the same?
No proliferation will occur –> radioactivity is NOT incorporated in DNA cells
Not a match –> radioactivity incorporated in DNA quantifying cell prolieferation
- What is the difference b/w Host vs. Graft (HVG) dz and Graft vs Host (GVH) dz?
- What are the 3 types of HVG dz?
- What is the most important thing to remember when trying to determine type of rejection?
- HVG = recipient cell attacks donor (ie the transplant)
GVH = donor T cells in graft proliferate and attack recipients tissue
- hyperacute, acute, and chronic
- Timeframe of onset of sx
Hyperacute HVG rejection ouccurs _______.
- What is the mechanism?
- What complement system is activated?
Immediatedly (ie upon operation –> thrombosis and occulusion of graft vessels)
1. Preformed Abs directed against donor tissue, caused by:
- ABO incompatibility (primary)
- recipient is sensitized to donor MHC by previous transplants, mutliple transfusions, or pregnancy
- CP –> Abs bind edothelial cells activating CP –> lead to death of endothelium
(**pre-existing Abs bind endothelial cells lining blood w/in min to hours*)
Acute HVG rejection occurs in ____ to ____.
- What is the mechanism?
- Is this direct or indirect allogenic presentation?
Days - weeks
- T cell mediated IR against foreign MHC
- following transplantation donor DCs migrate to LN draining the organ and stim. 1° recipient response
- both CD4+ and CD8+ T cells can cause graft rejection
- inflammation and leukocyte infiltration of graft vessels occurs
- Direct allogenic presentaiton
most common type
Chronic HVG rejection occurs in ____ to ____.
- What is the mechanism?
- Is this direct or indirect allogenic presentation?
- Chronic rejection does not respond to?
Months - years
- T cell mediated process
* causes intimal thickening, fibrosis, and occlusion of graft vessels –> ischemia of organ - Indirect presentation (DC of recipient take tissue debris from donor tisse to the LN and activate receipient T cells)
- Abs can also be involved –> deposition of complement in graft tissues
- non-immunologic factors:
- ischemia-reperfusion damage
- recccurance of dz that fuased failure of own kidney
- nephrotoxic drugs
3. Immunosuppressive therapy
- Why is the IR against a graft much more vigorous and strang than seen against a pathogen?
- What type of interaction b/w TCR and MHC mlcls allows for answer to q1?
-
Higher frequency of T cells recognizing the graft as foreign
* 1:100 - 1:1000 T cells response to allogenic APCs (specific against particular HLA - Low affinity interactions –> which are compensated for by mutiple interactions providing an avidity advantage
Immune memory of previous encounters w/ donor Ags is also impt
HVG:
- What are non-immune injuries to the graft called and what do these allow?
- What effector cell type provides humoral rejection? via which cytokines?
- What effector cell type provides the cellular rejection? via which cytokines?
- Which of these is MOST IMPT for ACUTE and CHRONIC T cell mediated responses?
- Danger signals –> activate endothelial cells and T cells enter the allograft
- Th2 –> IL-4, IL-5 and IL-10
- Th1 –> IL-2 and IFN-γ
- Th1
- With what kind of transplants does GVH dz often occur in?
- What causes this reaction?
- The reaction is directed against what type of recipient Ags?
- What type of pt’s is this often seen in?
- Acute of Chronic GVHD has epithelial cell death in skin, liver, and GI? What would be the common clinical manifestations seen in this type?
- What type of apoptosis occurs with GVH?
- Solid grafts –> BM, small bowel, lung or liver –> bc these naturally contain # of T cells
- Grafted mature T cells in tissue transplant w/ allo-Ags of host
- minor histocompatibility Ags (miHAs) of recipient
- Immunocompromised
- Acute –> rash, jaundice, diarrhea, GI hemorrhage
Chronic –> fibrosis and atrophy of affected organ
- FasL (on CTL) and Fas (on recipient DC) and granzyme mediated
- Immunosuppressive drugs are used for what?
- What are the 2 primary goals?
- Patients on immunosuppressive drugs are more prone to ______ _____ and have raised incidence of ______.
- prevention and tx of rejection after transplate
- Cnrtl IR against graft Ags and minimize drug’s side effects
- opportunistic infections; malignancy
- What is the MOA for steroids?
- What is the MOA for Cyclosporine A?
- What is the MOA for Anti-CD3 mAb OKT 3?
- What is the MOA for Tarcolimus?
- What is the MOA for Anti-CD25 mAb?
- What is the MOA for CTLA4-Ig fusion prtn?
- Anti-inflammatory (via inactivation of NF-κB--> no activaiton of IL-2 and other pro-inflammatory genes)
- Inhibits IL-2 gene transcription (block activation of NFAT –> no activaiton of IL-2 and other pro-inflammatory genes)
- Inhibits T cell activation and depletion (block signaling of TCR –> 1st signal)
- Inhibits IL-2 gene transcription (block activation of NFAT –> no activaiton of IL-2 and other pro-inflammatory genes)
- Inhinits IL-2R signaling (CD25 = IL-2 α receptor, so blocking the 3rd signal)
- Inhibition of 2nd signal of T cell activation (mediated by CD28:CD80/86)
- What is the first line of defense tx of transplant rejection?
- What is the general mechanism of glucocorticoids?
1. Corticosterioids
- prednisolone (cortisol) and methylprednisolone = anti-inflammatory glucocorticoids
- transcriptional inhibition of pro-inflammatory genes –> inhibits T cell proliferation –> induction of T cell apoptosis
- Inhibition of inflammation
- low [steroid] –> DNA-dependent regulaiton –> production of IκB inhibitor and IL-10 to induce anti-inflammatory proteins –> dec. inflammation
- high [steroid] –> block activation of NFκB –> no pro-inflammatory cytokines produced
- What drug is effective in prophylaxis and tx of allograft rejection in all types of SOLID ORGAN TRANSPLANTS?
- Its used as induction therapy and tx of acute or _____ resistant rejection.
- Anti-CD3 mAB –> OKT 3
- its an anti-CD3 mouse IgG2a mAB
- blocks CD3 signaling of T cells
-
steroid resistant
* 2nd line of defense
What drug/inhibitor is used for IMMUNOPROPHYLAXIS and is a basic component of immunosuppressive protocols in all organ transplants, that has a side effect of nephrotoxicity (kidney toxicity leading to graft loss) and is isolated from fungus species?
Cyclosporine A (CsA)
- peptide from fungus species
- inhibits calcium-dependent pathway of T cell activaiton
- It forms a complex = calmodulin-calcineurin
- this complex inhibits translocaiton of NFAT into nucleus (which is impt for T cell induction)
- inhibits production of cytokines IL-2, 3, 4, 5, IFN-γ, TNF-α, and GM-CSF
**prevents activation of T cells***
What drug is used in all types of organ transplants for maintenance immunoprophylaxis and tx of actue rejection, that has a side effect of nephrotoxicity (kidney toxicity leading to graft loss) and is isolated from Steptomyces ssp. species?
Tacrolimus = macrolide lactone
- simialr to CsA –> as it inhibits Ca+2-dependent pathway of T cell activation
- forms a complex that inhibits translocation of NFAT to the nucleus
- inhibiting IL-2, 3, 4, 5, IFN-γ, TNF-α, and GM-CSF
- **prevents activation of T cells***
What drug prevents interaction of CD28 w/ CD80/86 inhibiting the second signal of T cell activation?
CTLA4-Ig Fusion Prtn
- only signal 1 is received
- no activaiton of T cell –> apoptosis and anergy
