Transplantation and Transfusion Reactions Flashcards
what is an autograft
self tissue transferred from one body site to another in an individual
what is an isograft? (syngeneic graft)
tissue transfer between genetically identical individuals
what is an allograft?
allogeneic graft, tissue transfer between genetically different members of the same species
what is a xenograft?
tissue transfer between members of different species
what does rejection time depend on?
tissue involved – skin grafts occur faster and more often than others
describe the basic steps of rejection?
- revascularization followed by immune cell tissue infiltration by lymph, PMN, monocytes
- decreased vascularization as a result of the immune activity
- tissue necrosis within 2 weeks, rapid rejection occurs if 2nd transplant attempted (memory)
what type of reaction is a hyperacute rejection?
type II
what mediates hyperacute rejections?
preexisting, circulating antibodies that bind to blood group Ag within capillaries of the grafts
what category does ABO reaction fall into?
hyperacute reaction - type II
why is blood typing important for organ transplants?
ABO blood group Ag are present on RBC AND endothelial cells of donor organs, and Ig against these Ag can destroy the organ
what is the mechanism of hyperacute rejection?
IgG binding recruits C1q for complement activation and fixation. C3a/C5a recruit neutrophils and macrophages which promote inflammation. macrophage releases platelet activation factor which causes platelet aggregation, and blood clots form. clots prevent vascularization of the graft and ischemic necrosis develops.
how are pre-existing Ig against alloAg made?
blood transfusions or previous organ transplant can induce Ig against HLA of donor cells
how are MHC possible alloantigens?
each person expresses MHC proteins that can seem foreign due to MHC restriction in the thymus. (T cells are trained to recognize Ags displayed only on the person’s specific MHC mol, other MHC = alloAg
which MHC types are most likely to be recognized as alloantigens
HLA-A, HLA-B, HLA-DR
other than MHC, what other protein is targeted in rejection?
minor histocompatibility Ag (mHA) aka non-MHC antigens
could be glycoproteins
what is an example of mHA rejection reaction?
blood transfusion mismatches
what is the first step of acute rejection>
direct recognition of alloantigens by alloreactive T cells (CD4 and CD8) reacting to allogenic APC with allogeneic MHC
what is normal t cell activation
TCR recognition of self MHC and peptide leading to normal T cell activation (MHC and peptide both fit normally)
what the 1st option for recipient T cell activation to graft
T cell recognizes allogeneic MHC molecule whose structure resembles the self-MHC foreign peptide complex. the TCR has actually bound the MHC structure itself, not the peptide. recognizes graft MHC directly
2nd option for recipient T cell activation to graft?
T cell recognizes a structure formed by both allogeneic MHC molecule and bound peptide. TCR recognizes both the graft MHC itself and the peptide.
what type of reaction is acute rejection?
type II and IV
when does acute rejection occur?
first few weeks after transplantation
what mediates acute rejection?
B and T cells
what is the principle cause of early graft failure?
immunosuppressive drugs given before and after transplant
what is the B cell mechanism of acute rejection?
IgG binds to Ag in blood vessels, activates complement which recruits neutrophils and macs+MAC to lyse cells
what is the T cell mechanism of acute rejection
Th1 produce:
1. IFNgamma, which activates macrophages (inflammation) and increases MHC expression of grafts (CTL targets)
2. TNFalpha which induces graft apoptosis
3. CTL and NK cells lyse graft cells directly
TARGET IS BLOOD VESSELS
primary target of chronic rejection>
blood vessels
when does chronic rejection occur?
months to years after transplantation, will occur inevitably
what mediates chronic rejection?
immune complexes and T cells (cd4)
why is there a progressive loss of graft function in chronic rejection?
ECM accumulation in graft tissue (fibrosis of graft) due to series of inflammation and repair over time. this also includes arteriosclerosis and occlusion
how does indirect recognition of alloAg work?
INDIRECT RECOGNITION OF ALLOAG: donor DC in lymph nodes undergo apoptosis which frees donor Ag. the recipient DC acquire HLA II peptides and present them to T cells.
DIRECT RECOGNITION OF ALLOAG: wanes with time as many of the donor DC are replaced with recipient DC. INDIRECT RECOGNITION PROCEEDS
mechanism of chronic rejection?
apoptotic donor DC and acute response, soluble graft Ag activate B cells and bind Ig to form immune complexes and are captured/presented by recipient DC to T cells.
1. immune complexes activate complement.
2. chronic Th1 means chronic IFNgamma and TNFalpha, which stimulates proliferation of smooth muscle cells surrounding the arterioles of the graft.
3. necrosis (d/t occlusion of vessels) triggers fibroblasts (wound healing)
TISSUE FIBROSIS AND ARTERIOSCLEROSIS CAUSES ISCHEMIC DAMAGE AND ORGAN FAILURE.
what causes graft vs host disease? (GVHD_
stem cells from bone marrow or blood (stem cell transplant) generate T cells. some tissues will have donor T cells present when transplanted. if donor T cells present within graft, donor T cells respond to MHC on graft recipient cells and activate. donor T cells attack and lyse recipient cells and damage recipient tissues.
when does GVHD occur?
within 4 weeks but up to 3 months, because stem cells are making new cells and depends on how many T cells
key: make sure to remove T cells on graft?
what has a major impact in graft loss?
HLA-A, HLA-B, HLA-DR
when do HLA-DR mismatches occur?
most important first 6mo after transplant
when do HLA-B mismatches occur?
first 2 years
what impact does HLA-A have on graft?
long term graft survival
what tests are done to tissue type for MHC phenotype?
- microcytotoxicity test
- genetic analysis
- cross matching
how to do microcytotoxicity test?
donor and recipient WBC added to separate well. one anti-HLA Ab added and incubated with complement. if Ab bind to specific HLA, complement is activated and cells lyse, turning blue. if both tissues turn blue, it’s a match, both tissues have that HLA type.
how to do genetic analysis?
PCR amplification of pt DNA using HLA-specific primers and compare sequence/bands on gel
why is cross matching important?
used to rule out preformed Ab against donor HLA
what are important immunosuppressive therapies?
- cyclosporine and tacroliminus (FK506)
2. corticosteroids
moa of cyclosporine and tacroliminus
interferes with calcineurin action to inhibit NFAT activation, therefore block T cell activation
MOA corticosteroids
increases IkB to prevent NFkB activation, block lymphocyte homing, and block T cell activation
what can cause serum sickness?
therapeutic Ig
7-10days after large protein administration with differences in recipient Ig to donor Ig (same species or not)
when do transfusion reactions occur?
within 15min or 50mL of blood transfer
symptoms of transfusion reaction?
fever, chills, Ha, hypotension, tachycardia, tachypnea, CP, LBP, anxiety, hemoglobinuria, facial flushing, itchy hives or rash, shock
what is the #1 reason for unsuccessful transfusion?
human error due to mislabeled blood or wrong pt
what is the #1 most common allogeneic tissue transplant in medicine?
blood transfusions
what is the most common transfusion transmitted infection?
bacteria contaminating platelets
since they are stored at room temp
what is acute hemolytic transfusion reaction (AHTR)
ABO/Rh mismatch or anti-RBC (non-ABO)
how much blood could cause AHTR?
as little of 10mL
symptoms of AHTR?
fever, increased pulse rate then chills, dyspnea, rash, hives, chest/flank pain, discomfort at infusion site, anxiety, progress to shock
what causes febrile non-hemolytic transfusion reaction? (FNHTR)
cytokine accumulation during storage of cellular components (from storage of whole blood) AND/OR preformed Ig response of recipient to donor HLA
symptoms of FNHTR
fever and chills bc of cytokines (is a diagnosis of exclusion)
what Ag do all RBC have?
H antigen
what Ag does Type O blood have?
RBC with H Ag
what Ag does Type A blood have?
RBC with N Acetylgalactosamine added to H Ag
what Ag does Type B blood have?
RBC with D-galactose added to H Ag
what Ag does Type AB blood have?
RBC with both N Acetylgalactosamine and D-galactose added to H Ag
what is Landsteiner’s rule?
substances are present in nature which are so similar to blood group Ags which result in the constant production of Ig to blood group Ags that they don’t possess
what Ag does type A blood have?
Antigen A
what Ab does Type A blood have?
anti-B antibody
what blood can type A blood have?
can have A or O.
cannot have B or AB
what Ag and Ab does Type B blood have?
Ag B
anti-A Ab
what blood can type B have?
can have B or O
cannot have A or AB
what Ag and Ab does Type AB have?
both A and B Ag
neither Ab
what blood have Type AB have?
can have A, B, AB, O (universal recipient)
what Ag and Ab does Type O have?
neither Ag
both A and B antibodies
what blood can Type O have?
can only have O blood
can donate to everyone! universal donor
how does ABO reaction cause lysis of RBC?
IgM/IgG bind to group Ag and C1 initiates classical pathway of complement. AND preexisting Ig against blood group Ag overwhelms normal inhibition of the classical pathway
what is Rh blood group system?
complex SET of RBC surface proteins that help maintain the cell membrane
what Rh Ag exist?
there are 50, but only 5 have high immunogenicity (cause the majority of clinical issues)
D>c>E>C>e
what is used to designate ABSENCE of D Ag?
d
what is meant by Rh+ or -?
presence or absence of D Ag
what is R1?
D positive haplotype with DCe
what is R2?
D positive Haplotype with DcE
what is R0?
D positive haplotype with Dce
what is r’?
D negative haplotype with dCe
what is r”?
D negative haplotype with dcE
what is r?
D negative haplotype with dce
what haplotype is dominant?
D Ag is dominant (R vs r)
what haplotype is most common in caucasians?
R1 (DCe)
what haplotype is most common in AA?
R0 (Dce
what haplotype is most common in asians?
R1 (DCe)
what is the most common blood type in the US?
O+ at 38%
A+ at 34%
aka Rh+
what transfusion reaction occurs less than 24hours post transfusion?
immunological acute allergic reaction occurring seconds to minutes after transfusion.
what causes mild urticarial acute transfusion reaction?
hypersensitivity to plasma proteins (type II)
how to treat mild urticarial reaction?
stop giving blood, antihistamines, if resolves, resume
what causes severe anaphylaxis acute transfusion reacitons?
allergen transfused to sensitized patient
Ig response to plasma proteins
transfusion of IgE
symptoms of severe anaphylaxis ??
suddent onset hypotension, cough, bronchospasm, laryngospasm, angioedema, urticaria, N/V/D, abd cramps, poss shock, LOC death
treatment for severe anaphylaxis in acute transfusion reaction?
stop transfusion, supplemental O2, antihistamines, adrenaline and corticosteroids as needed
what causes transfusion related acute lung injury? (TRALI)
3 events involving anti-HLA or anti-HNA Ab in donor’s blood plasma directed against recipient cells. Ab bind to neutrophils in lungs, complement released, lyses PMN/activate PMN which release oxidases and proteases that destroy blood vessels and fluid fills airways due to leaky endothelia.
treatment for TRALI
stop transfusion, supplemental O2, ventilation.
test the donor and recipient serum for HLA and HNA Ab
reason to infuse packed plasma (RBC)
increase the amt of RBC after trauma or surgery or to treat severe anemia
reason to infuse fresh frozen plasma
to correct a deficiency in coagulation factors or to treat shock due to plasma loss from burns or massive bleeding (filler or volume)
reason to infuse concentrate of platelets
to treat or prevent bleeding due to low platelet levels, to correct functional platelet problems
what would be a concern with fresh frozen plasma?
be careful of preexisting Ab
what would be a concern with concentrate of platelets?
can be contaminated easily
appropriate uses of RBC as therapeutic product?
- tx of symptomatic anemia
- prophylaxis in life threatening anemia
- restoration of oxygen carrying capacity in case of hemorrhage
- exchange transfusion - sickle cell, severe parasitic infection (babesiosis, malaria), severe methemoglobinema, severe hyperbilirubinemia of newborn
what conditions are NOT indicated for RBC transfusions?
iron deficiency anemia or vitamin B12 or folate deficiency anemia
what does infusion of 1 unit of RBC result in?
increase of Hb by 1g/dl
increase of hematocrit by 3%
what is 1 unit of RBC?
450-500 mL of whole blood
what factors should be considered before giving RBC transfusion?
- hypoxia - is pulm function not normal?
- volume of blood loss - how much?
- oxygen consumption - prevent anemia!! fever, chills and shivering can alter o2 use and increase need for RBC
- hemoglobin levels less than 7gm/dL
what is the purpose of pretransfusion testing?
prevent incompatible RBC transfusion, avoid AHTR and DHTR
when would a sample need to be collected for transfusion?
within 3 days
if recipient has been transfused in the preceding 3 mo
has been pregnant within the preceding 3 mo
hx is unclear
how is ABO typing accomplished?
1st, direct agglutination studies - forward and reverse typing
then Rh testing
what is forward typing?
testing pt RBC with anti-A and anti-B antisera
what is reverse typing?
testing pt serum for anti-A and anti-B
is a confirmation test for forward typing
what if ABO typing is the only testing performed?
donor RBC will be compatible with recipient plasma in 97% of cases
what do serum tests look at?
serum antibodies
what do RBC test look at?
RBC antigens
what is step 2 of compatibility testing
assess presence or absence of D Ag on recipient RBC using anti-D Ag antibody.
what occurs if pt is Rh-?
pt serum will be tested by Coombs test for the presence of anti-D Ag Ab , esp if previous transfusion or pregnancy
benefit of coombs test
to assess for anti-RBC IgG, because anti-RBC IgM efficiently agglutinates RBC but IgG does not
what is direct coombs test used for?
used to detect IgG or C3 bound to the RBC in vivo
why does IgG not spontaneously agglutinate?
have strong electronegative charges on RBC surfaces, prevents cells from coming in close contact
what does the coombs reagent contain?
(Antiglobulin reagant)
cocktail of monoclonal antibodies directed against human IgG/IgM and C3
characteristic of immune-mediated transfusion reactions?
DAT-positive (non-immune are DAT negative)
what is the coombs test especially effective for?
to detect presence of incomplete anti-D Ag IgG
in Rh+ babies from Rh- mothers)
steps of direct coombs test
- blood sample from pt with immune mediated hemolytic anemia. have Ab attached to Ag on RBC surface.
- washed RBC are incubated with anti-human Ab (coombs reagent)
- RBC agglutinate - antihuman Ab form links between RBC by binding to the human Ab on the RBC
what is the indirect antiglobulin test? (IAT)
the indirect coombs test that is more specifically used in pretransfusion screens, and cross matching of donor and recipient before transfusion
what is the indirect coombs test used for?
to detect Ab present in patient serum which can form antibody-Ag interactions IN VITRO
steps of indirct coombs test?
- recipient serum obtained containing Abs
- donor’s blood sample is added to the tube with serum.
- recipient’s Ig that target the donor’s RBC form Ab-Ag complexes.
- anti-human Ig (coombs reagent) is added to the solution.
- agglutination of RBC occurs because human Ig are attached to RBC>
