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Flashcards in Fetal Transplant Deck (29):

How can you determine if a donor is a good match to transplant recipient?

Detection of recipient antibodies that might cause rejection of a transplanted organ (ELISA, flow cytometry)
Determination of the degree of compatibility between the recipient and the donor (flow cytometry, DNA sequencing)

There are two ways to “type” or detect MHC or HLA specificities on mononuclear nucleated cells. The number of matched MHC loci, especially the Class 2 ones (also known as DR), between donor and recipient can be used to predict graft acceptance. The more loci matched the better, but MHC Class 2 (DR) matches are the most strongly predictive of graft survival.

Originally, the source of the antibodies used to detect HLA specificities were usually from women with multiple pregnancies who reacted to a paternal HLA antigen.

More recently, tailored monoclonal antibodies are available against specific MHC loci.

Tissue Typing Laboratories are now using flow cytometry, ELISA and molecular methods to decrease time of analysis and increase sensitivity
and decrease costs but you need to understand the fundamentals of detecting HLA antibodies.

The Mixed lymphocyte reactions ("In vitro") transplants:

Mixed Lymphocyte Culture (MLC) - a transplant in vitro.
The primary concept of this assay is that differences in the HLA (MHC) class I & II (particularly HLA-DR) antigens between the donors of the
cells used in the assay will stimulate T lymphocytes to synthesize DNA and divide. The MLC is designed to quantitate the amount of cell division as measured by newly synthesized DNA in responder lymphocytes when exposed to irradiated stimulator lymphocytes. In a solid organ transplant scenario (eg. heart, kidney) the responder cells
are the recipient cells and the stimulator cells are from a potential donor.


What determines hyperacute vs acute rejection?

Which is mediated by antibodies?

HYPERACUTE (within 24 hours)—Ab plays a critical role. secondary immune response bc body has memory against this tissue. that’s why Pre-test for Ab test is important

ACUTE: Defined by sudden (10-90 days) appearance of effector cells in the graft. Vigor depends upon DR mismatch, gender, intensity of immunosuppression


Describe mechanism of rejection involving naive and memory lymphocytes.

Alloimmune responses involve both naive and memory lymphocytes. In the graft and the surrounding tissues, dendritic cells of donor and host origin
become activated and migrate to T-cell areas of secondary lymphoid organs. There, donor antigen-bearing dendritic cells engage alloantigenreactive
naive T cells. Naive T cells are optimally triggered by dendritic
cells in secondary lymphoid organs, but antigen-experienced memory T and B cells (perhaps by past blood transfusions or pregnancy) may also be
activated by other “non-professional” APC such as endothelium of the transplanted organ.


The mammalian immune response has multiple effective pathways to
prevent engraftment of foreign organs. Describe the direct and indirect methods.

The MHC of the transplanted organ, especially the MHC on the "passenger" leukocytes carried into the recipient from the donor, function as alloantigens and are recognized by the immune system in two ways:

Direct - activation of the immune system by the foreign
MHC marker itself without any form of MHC processing or presentation. Large
numbers of CD4 T-cells will react with foreign MHC, possibly on the
process of the molecular mimicry.

Standard recognition by the "indirect" method - alloantigens are phagocytized, processed and represented in the context of Class II MHC antigens by antigen presenting cells to CD4 T cells.


What does intensity of rejection depend upon?

Would a reaction be more intense/destructive if Th17 were more dominant or if B cells were the dominant cell?

The intensity of rejection will depend upon the ratio of Th1, Th 2 and Th17 cell activation counter-balanced by T regulator inhibition. For example, if the dominant cell is Th17, the rejection might be more destructive (more neutrophils) than if B cells were the dominant cell.


Once either indirect or direct alloantigen activation of the immune system
occur, what immune response is initiated? What type of hypersensitivity reaction?

CD4 Th-cells are mandatory participants in all forms of cellular rejection.

IL-12 driven T Cell mediated Macrophage immunity (delayed
hypersensitivity) occurs early

Activation and clonal expansion of CD8-alloantigen specific T-cells
follows, driven by CD4 Th1 cells and IL-21.

Recent evidence strongly suggests that the Th17 cell and IL-23 may rewrite the story of rejection immunology.Th17 is a very pro-inflammatory cell and if it is the predominant cell in a
rejection episode, graft damage may be severe.

Th2 cells provide co-stimulatory signals, IL-4 & 21, for alloantigen
specific B-cells which then produce alloantibody

NK-cells participate in varying degrees in transplant rejection,
however, they are not mandatory for a successful rejection of a transplanted organ.

The cumulative effect is: 1) activated macrophage mediated graft destruction, 2) CD8 antigen specific graft cytolysis, 3) Th17 mediated inflammation and, 4) antibody mediated, graft destruction
either by complement and/or Fc receptor activation of cell death mechanisms.

Induction of T regulator cells- this highly dependent upon
individual “immune response” genes of the recipient and the
disparity of the MHC antigens between donor and recipient.


Graft arterial occlusions occur sometimes in the hyperacute response when antibodies against donor blood antigens bind vascular endothelium of graft, initiating an inflammatory response that occludes blood vessels.

How does a chronic mechanism differ from hyperacute reaction?

CHRONIC….insidious and caused by mechanisms probably different than acute rejection, usually caused by graft arterial occlusions, which results from the proliferation of smooth muscle cells and production of collagen by fibroblasts. This process, termed accelerated or graft arteriosclerosis, results in fibrosis which can cause ischemia and cell death. The major problem in solid organ transplantation today

fibroblast and fibrosis, collagen deposition in the vascular environment and also w/in tissue so whole lung thats supposed to be working for air exchange doesn't work anymore and is just distinctive scar… chronic rejection is big problem .

The pathology of hyperacute rejection is characterized by widespread vascular injury brought about by alloantibody mediated endothelial damage.


What drug can wipe out acute rejection?

drug FK506- wipes out acute rejection)


Describe graft-vs-host disease. Given an example.

Please remember that this situation can occur when an Immunoincompetent host receives a transfusion!(if it is
Not depleted of lymphocytes first)

When bone marrow is transplanted the T cells in the transplant attack the recipient's tissues.

radiate patient w v high dose to remove all lymphomas and all HSC. wipe out blood system. then repopulate patient w new bone marrow. or use umbilical cord blood. those are good sources of HSC. problem w this approach is sometimes bone marrow is v good source (niche) for memory T cells ..mature T cells that function effectively
if you don't remove those memory T cells, they will go into the patient. then those T cells coming from bone marrow will start attacking the recipient tissues. for those T cells that is an allogenic condition… even though from whole organ system, that is allopathic for T cell coming here and that causes graft vs host.


What will transplantation of an A, B, or AB organ into an "O" individual result in?

a patient who is blood
group O normally has circulating antibodies to blood group A and B. antigens. These antigens are not only on erythrocytes, but are widely distributed on all tissue cells. Transplantation of an A, B, or AB organ into an "O" individual will result in an immediate reaction between the transplanted organ's A or B determinants and recipient antibodies.


When might antibodies with reactivity to MHC antigens be present in patients prior to transplant?

Antibodies with reactivity to histocompatibility (MHC) antigens can also be present in some patients prior to transplant. These patients have
usually been sensitized by repeated blood transfusions or multiple


What characterizes the acute reaction?

Acute rejection is defined by the sudden appearance of anti-donor organ
immune effector cells during the first three weeks after grafting. The
rejection sequence, especially early after grafting, is initiated when host recipient CD4 T-cells react with alloantigens, either directly or indirectly,
and mediate a TMMI-type response. Simultaneously, alloantigen specific
CD8 cells attack the graft, TH17 cells promote an inflammatory reaction
and B-cell alloantibody appears after alloantigen specific B-cells take up
residence within the graft.

The mix of cell populations, the vigor of their response, and
frequency of rejection is orchestrated by a complex interplay between MHC differences, especially between HLA- D
(MHC-II) loci of donor and recipient.


At what stage of rejection might you be most likely to see diffuse, widespread
arteriolar narrowing caused by intimal thickening of the vessel? Hyperacute, acute or chronic?



What signals or cytokines might be able to override Th1 or CD8 responses to prevent rejection?

Provide inhibitory second signals (CTLA-4) or cytokines (IL-10 & TGF-beta) to override Th-1 and CD8 responses


What type of rejection will occur with a xenotransplant?

Non-primates, for e.g., pigs, have anatomically suitable organs for
xenografting but unfortunately have rich endothelial displays of the α-gal epitope. Thus the attempt to transplant these organs into humans is thwarted by hyperacute rejection.


Does trophoblastic tissue display HLA-A, B, C, D, G?

Trophoblastic (fetal origin) tissue (the maternal-fetal
interface) does not display "classic" HLA-A, B, or C
fetal molecules because the MHC at the interface is down regulated.

Trophoblastic (fetal origin) tissue (the maternal-fetal
interface) displays only a "non-classical" HLA system,
HLA-G, that has an inhibitory motif for maternal NK cells. Wherever trophoblastic tissues invade the uterine wall to establish and maintain pregnancy these HLA-G molecules are displayed.


How does TGF-beta influence NK cells during pregnancy?

in the gravid uterus under the influence of progesterone
and especially uterine produced TGF-B, they convert to a markedly different NK cell and ultimately will
comprise about 70% of all lymphocytes in the
endometrium during pregnancy.


Describe NK cells in pregnant uterus. What CD do they not express? How are cytotoxic receptors inhibited?

In the pregnant uterus, they do NOT express CD16, the
Fc receptor necessary for antibody-directed cytotoxicity (ADCC) and their cytotoxic receptors are inhibited by HLA-G. Their cytokine profile becomes inhibitory also.
They are found in increased numbers at all
trophocytoblastic interfaces and are believed to have
regulatory and tolerogenic functions that prevent
immune cytotoxic attack on fetal structures. Pregnancy
NK cells also produce angiogenic factors that support successful pregnancy by increasing blood supply to the
fetal supporting structures.


Describe the types of T cells and innate cells and CD cells that increase in uterine wall during pregnancy. What do these secrete? What results?

There are increased numbers of maternal gamma-delta T cells, macrophages and paternal antigen specific CD4, 25
regulatory cells in the uterine wall during pregnancy. They secrete large amounts of immuno-suppressive cytokines, especially IL-10 and TGF-B, and thereby actively inhibit maternal alpha beta CD4 and CD8 T cell attack on the fetus. Fetal trophoblastic tissue also produces IL-10 and TGF-B. These cytokines strongly promote the continued presence of Treg cells.


What hormone strongly suppress local and systemic Th-1 type


Pregnancy induced hormones, especially progesterone, strongly suppress Th1 reactions. Progesterone also inhibits complement reactions.


The mother has suppressed Th1 and Th2, suppressed Th2 and normal Th1, normal Th2 and suppressed Th1?

Pregnancy induced immunoregulatory hormones, especially progesterone, strongly suppress local and systemic Th-1 type
responses. Placenta-derived factors also decrease Th-1 responses both in the uterus and systemically. IL-10, a suppressive cytokine, is also increased in the peripheral blood uterine during pregnancy. The net result to the mother is that she has suppressed Th1
responses but relatively normal Th2 responses.

Th2 dominant with strong humoral responses but suppressed TMMI,
Th17 and cytotoxic responses. Alterations of this state can strongly influence pregnancy


Why doesn't the maternal immune system attack paternal antigen that escapes into maternal blood? Especially in subsequent pregnancies with the same male?

Increased numbers of paternal MHC antigen specific maternal T
regulatory cells can be found circulating in maternal blood and
concentrated in the uterus during pregnancy. The paternal specific T
regulators rapidly decline postpartum but persist as memory T cells that can rapidly expand in a subsequent pregnancy with the same male.

spontaneous abortion reported when these Treg not generated toward paternal antigens..repeated spont. abortion in some cases bc lack of Treg generation which causes this abortion process.

Expansion of paternal-specific T regs during subsequent pregnancies may determine a successful outcome and decreased pregnancy complications if the father is same or similar to the initial father. Conversely, subsequent different fathers may not induce rapid expansion of maternal paternal
specific T regs and this may be associated with adverse outcomes


How is complement inhibited in pregnancy? (What factors, etc..)

Progesterone also stimulates the surface cells of the uterine endometrium to display decay accelerating factor (DAF or CD55- see complement lecture) which in turn inhibits complement mediated cell death


What will conversion of a maternal-fetal Th2 bias to a Th1 bias with dominance
of INF-γ at the fetal-maternal interface result in?

is associated with
inability for successful implantation and/or fetal resorption.


Discuss what the TH-2 bias dominant during pregnancy can lead to.

can lead to exacerbation of
maternal diseases dependent on Th-1 for suppression - tuberculosis,
leprosy, toxoplasmosis and influenza are examples.


What would result from an inability to generate maternal T regulatory cells?

fetal loss. Reconstitution of maternal T regs in a
murine abortion model leads to successful pregnancy.


What might infection of fetus lead to by a specific pathogen?

Infection of the fetus may lead to tolerance to the infecting pathogen and that could subsequently prevent the infant or later, as a child then adult, from responding appropriately to infection with that pathogen.

Zika virus is a recent case came to our attention.


When might a spontaneous abortion occur?

spontaneous abortion reported when these Treg not generated toward paternal antigens..repeated spont. abortion in some cases bc lack of Treg generation which causes this abortion process.


What are the best strategies to prevent rejection? Discuss roles of CD28, CTLA4, MHC (what type).

Optimal MHC matching, especially DR

Co-stimulation blockade (CTLA-4-Ig) = induction of immune check point

Induce tolerance by manipulating Tregs

CTLA-4 (tolerance) this is molecule that causes immune checkpoint! that basically causes inhibition of activation (co-stimulatory molecule)

CD28 provides costimulation, CTLA4 will block it. so if you have

CTLA4 mimicking molecule like CTLA4Ig, that will work just like CTLA4 and that blocks T cells from being active

( CTLA4-Ig is a fusion molecule… CTLA4 is transurface molecule. but CTLA4-Ig is immunoglobin diffusion becomes soluble so can inject as drug and works just like CTLA4 )