immunology of transplantation parts 1/2 W3 Flashcards
components of the innate immune system?
macrophages
neutrophils
complement and natural antibodies
components of the adaptive immune system?
dendritic cells (antigen presentation)
T cells (helper and cytotoxic T cells)
natural killer cells (cytotoxic)
B cells (antibody generation and memory)
what is the major histocompatibility complex in humans?
histocompatibility locus antigen (HLA)
HLA features?
molecules imprint individuality on cells and are pivotal in the generation of immune responses
very polymorphic - there are many different variations possible at each gene locus
categories of HLA molecules?
HLA class I and class II
class I HLA molecules? features?
HLA-A, HLA-B, HLA-C
expressed by most somatic cells of the body
used to present peptides from internally processed proteins
class II HLA molecules? features?
HLA-DP, HLA-DQ, HLA-DR
expressed by antigen presenting cells (DCs etc) that constantly sample their microenvironment
used to present antigenic peptides derived from digested material (including pathogens, abnormal or foreign cells)
peptide groove on HLA class I molecules?
small peptide derived from internally processed protein sits in peptide groove. this is what is looked at by passing immune cells.
what happens if class 1 HLA molecule is associated with virus-derived protein?
the cell is recognised as infected and will be killed by cytotoxic T cells
peptide groove on HLA class II molecules?
used by antigen presenting cells (DCs etc) to present antigenic peptides derived from digested and processed material
cell surface expression of peptide derived from pathogen or foreign cell will stimulate a T cell immune response.
what happens at a T cell synapse?
other molecules have to be engaged to create a signal strong enough to engage and ensure the T cell is activated.
ways a T cell can kill another cell expressing viral protein or abnormal cell?
use FasL (Fas ligand) which can induce cell death
can release tumour necrosis factor which can induce death
molecules perforin and gz B can punch a hole in the membrane, pass through and induce cell death.
t cell activation pathway?
dendritic cell finds abnormal cell, takes up material and present the antigen which initiates T cell responses. T cells are antigen specific, facilitated by production of IL-2 which is required for their proliferation. causes clonal expansion of T cells with unique specificity. circulate body, find target and exert effector functions. once infection is eradicated then these clones die, but memory T cells remain.
key principles of transplant immunology?
rejection of transplanted organs is directed at specific proteins called antigens
rejection is donor specific
rejection may be cell or antibody mediated
rejection exhibits memory - ie a 2nd similar transplant is rejected more rapidly (due to rapid generation of cytotoxic antibodies recognising transplant)
how is the best match for kidney transplants found?
all patients on transplant waiting list have their HLA tissue type on a central UK database
what is HLA profiling used for
used to allocate kidneys. less important for other organs eg liver as they are less immunogenic.
explain level of mismatch?
if all HLA-A, HLA-B and HLA-DR loci are the same between the donor and the recipient then it is a 0-0-0 mismatch.
if they are all different then it is a 2-2-2 mismatch, this reduces survival rates.
immunosuppression treatment for transplants?
corticosteroids
calcineurin inhibitors (CNI) - tacrolimus
anti-proliferative agents
various monoclonal and polyclonal antibodies
corticosteroids effects?
kill lymphocytes
interfere with T cell activation and gene transcription
powerful anti-inflammatory agents
calcineurin inhibitors (CNI) - tacrolimus - effects?
inhibit T cell activation by interfering with intracellular signalling pathways
what anti-proliferative agents do we use? what are their effects?
mycophenolate mofetil
inhibit clonal expansion of T cells
monoclonal and polyclonal antibodies - effects?
directed against:
-IL-2 receptor blockers (IL-2 stimulates clonal expansion of T cells)
-T cells (cytotoxic complement fixing antibody)
-co-stimulatory molecules
transplantable organs/tissues?
kidney
pancreas
liver
lung
heart
small bowel
cornea
faces, arms etc (more specialised)
how is patients suitability for transplant assessed?
age
cause of renal failure - can condition reoccur in transplant?
comorbid disease
history of infections and tumours
urological disease
renal conditions which can and can’t reoccur in transplant?
cannot reoccur:
- polycystic kidneys
can reoccur:
-atypical hemolytic uremic syndrome (aHUS)
-focal segmental glomerular sclerosis
additional investigations for patients potentially suitable for transplant?
cardiac - exercise ECG, myocardial perfusion studies
angiography
urodynamic studies
tumour markers, imaging etc
2 broad categories of transplant?
cadaveric donor - most common. (DCD/DBD - donated after cardiac/brain death)
living related donor - typically a kidney transplant
which type of transplant has a better long term outcome?
living donor
biochemistry criteria for kidney transplant?
blood group compatible
immunological ‘X-match negative’
immunological ‘X-match negative’ meaning?
find out if recipient has any antibodies against HLA molecules that will react with the cells of the donor organ?
how is immunological cross matching carried out?
take serum from potential recipient and donor lymphocytes from donor. add a source of complement. vital dye enters dead cells stains them green, if this occurs then the cross match is positive, HLA antibodies are present.
how many patients on renal waiting list have anti-HLA antibodies?
~30%
how may a person obtain anti-HLA antibodies?
previous transfusion
pregnancies
previous transplantation
how is the presence and level of antibodies assessed?
flow cytometry
microbeads coated with HLA antigen incubated with patient serum
wash beads
incubate with PE conjugated anti-human IgG. if this binds then shows florescent signal indicating the patient has this antibody.
types of rejection?
hyperacute rejection (shouldn’t happen)
acute rejection
chronic rejection
when does hyperacute rejection occur? what happens?
transplant carries antigens to which the recipient is already sensitised.
cytotoxic antibodies bind endothelial cells and induces complement activation, platelet aggregation and intravascular thrombus formation.
transplant often destroyed on operating table.
features of acute rejection? what causes for this do you need to exclude?
rise in creatinine
exclude other causes:
-dehydration (examination)
-renal obstruction (ultrasound)
-vascular catastrophe (Doppler)
-drug toxicity (tacrolimus levels)
take kidney biopsy!
biopsy of acutely rejected kidney?
areas of many infiltrating cells directly targeting kidney
what can occur in the tubules during acute kidney transplant rejection
tubulitis - lymphocytes can invade tubule, cause severe destruction.
how can we look at antibody rejection
when antibody binds to endothelium it activates compliment leading to deposition of C4d. this can be stained for us to see where previous antibody has bound.
treatment of acute rejection?
high dose methyl prednisolone (anti-inflammatory)
change to more potent immunosuppressive agent or increased dose
anti-T cell antibody (but increased risk of infection and tumours)
remove antibodies through plasma exchange (if rejection is antibody mediated)
