Solid Organ Transplantation and Reference Interval Studies

Comprehensive practice flashcards covering solid organ transplantation immunology, graft rejection types, histocompatibility testing, immunosuppressive therapies, GVHD, and clinical laboratory reference interval studies.

When and where was the first successful human solid organ transplant performed, and which organ was transplanted?

The first successful organ transplant was a kidney transplant performed in Boston in $1954$.

What are the three major clinical processes involved in solid organ transplantation?

1. Pre-Transplantation Evaluation
2. The Surgery
3. Post-Surgery Recovery

What role does the Rh factor play in blood typing during pre-transplantation evaluation?

The Rh factor does not matter in organ transplantation matching.

How frequently and up to what time point prior to organ transplantation must crossmatching be performed?

Crossmatching is performed multiple times up to $48\text{ hrs}$ prior to transplantation.

Which specific pathogens are screened during the serology component of pre-transplantation evaluation?

HIV, CMV (cytomegalovirus), and Hepatitis.

Why might a newly transplanted organ fail to respond to physiological stimuli promptly during post-surgery recovery?

It lacks native nerve connections.

What is an autograft, and what are typical examples?

A graft transferred from one anatomic position to another within the same individual (e.g., skin, hair, bone).

What is a syngraft (isograft)?

A graft transplanted between genetically identical individuals, such as monozygous (identical) twins.

What is an allograft (homograft)?

A graft transplanted between genetically different recipient and donor individuals belonging to the same species.

What is a heterograft (xenograft), and what is a common clinical example?

A graft transferred between individuals of different species (e.g., transplanting a pig heart valve into a human heart).

At which genetic loci are MHC Class I and MHC Class II antigens coded?

MHC Class I antigens are coded at HLA-A, HLA-B, and HLA-C. MHC Class II antigens are coded at HLA-DR, HLA-DQ, and HLA-DP.

To which effector cells do MHC Class I and Class II antigens present peptides, and which pathogen classes do they target?

MHC Class I presents peptides to CD8 ($T_c$) cells to target intracellular pathogens (viruses, tumors, parasites). MHC Class II presents peptides to CD4 ($T_h$) cells to target extracellular pathogens (bacteria).

What are minor histocompatibility (mHC) antigens, and how do they impact graft survival?

They are non-HLA polymorphic proteins within a species that can induce an immune response upon transplantation, mediating a slower pace of graft rejection.

What is MICA, on which cells is it expressed, and where is it absent?

MHC class I-related Chain A (MICA). It is expressed on endothelial cells, keratinocytes, fibroblasts, epithelial cells, dendritic cells, and monocytes, but is NOT expressed on T cells or B cells.

What are the time of onset, primary immunological mechanism, and therapeutic success rate of hyperacute graft rejection?

Onset occurs within minutes to hours ($< 48\text{ hours}$); it is a secondary humoral response mediated by preformed antibodies reacting with vascular endothelium, leading to thrombosis, ischemia, and necrosis; therapy success is $0\%$.

What are the time of onset, mechanism, and therapy for accelerated graft rejection?

Onset is $3\text{--}5\text{ days}$; mediated by preformed non-$C^+$ binding antibodies and cellular immunity (where donor-specific antibodies were low before transplant); treated with polyclonal antilymphocyte globulin, plasmapheresis, or cyclophosphamide ($60\%$ success).

What defines acute cellular rejection, and which immune cells predominate?

Onset occurs in $> 6\text{ days}$ (days to weeks), characterized by parenchymal and vascular injury, necrosis, and inflammation, with a predominance of CD8 cells, CD4 cells, and macrophages.

What histopathological hallmark characterizes chronic graft rejection, and what is its therapeutic success rate?

Graft arteriosclerosis featuring vascular smooth muscle cell proliferation, progressive fibrosis, and scarring; therapeutic success is $0\%$.

Which human tissue is categorized as the most immunogenic for transplantation, and which is the least immunogenic?

Bone marrow is the most immunogenic tissue; the cornea is the least immunogenic tissue.

Why does corneal transplantation uniquely evade immune-mediated graft rejection?

Corneal tissue is avascular and does not come into contact with the recipient's immunologic system.

What are the time constraints for donor heart transplantation, and how many mismatches are acceptable in cadaveric kidney transplantation?

A donor heart must be transplanted within $4\text{ hrs}$; cadaveric kidney transplantation allows zero or one mismatch.

Why are high doses of chemotherapy or radiation administered to recipients prior to bone marrow transplantation?

To prevent graft rejection, eradicate any residual cancer cells, and create space for the new marrow to engraft and proliferate.

What three conditions are required for the initiation of Graft-versus-Host Disease (GVHD)?

1. A graft source containing immunocompetent lymphocytes (e.g., blood products, bone marrow, organ transplant)
2. HLA differences between donor and recipient
3. An immunocompromised recipient unable to reject donor cells

What are the prominent clinical manifestations of Graft-versus-Host Disease (GVHD)?

Exfoliative dermatitis, erythema, diarrhea, liver inflammation, marrow aplasia, weight loss, malaise, fever, joint pains, and potential death.

How are blood products treated to prevent transfusional Graft-versus-Host Disease in susceptible patients?

Blood products are treated with gamma irradiation.

In a lymphocytotoxicity test for HLA typing, what indicates that patient cells are positive for a specific HLA antigen?

The uptake of trypan blue dye by cells that were damaged and killed through antibody-mediated complement ($C'$) activation.

What is the procedure and purpose of a mixed leukocyte reaction (MLR)?

It evaluates the degree of recipient T cell stimulation by donor cells by co-incubating Ficoll-Hypaque isolated lymphocytes at $37^\circ\text{C}$ for $5\text{ days}$, pulsing with tritiated thymidine, and measuring cellular radioactivity.

What are the distinct immunosuppressive mechanisms of corticosteroids, sirolimus, and monoclonal antibodies?

Corticosteroids inhibit antigen-driven T cell proliferation; sirolimus blocks the activation and proliferation of T lymphocytes; monoclonal antibodies specifically target the CD3 surface membrane marker.

What defines a reference interval (normal range) in clinical laboratory medicine?

The interval spanning the data points that encompass a specified percentage (usually $95\%$) of values observed in a healthy population.

How many study individuals are required to establish versus verify a laboratory reference interval?

Establishing requires $120$ to as many as $\approx 700$ study individuals; verifying can be performed using as few as $20$ healthy representative individuals.

What three criteria necessitate the evaluation of reference intervals and corrective action by a clinical laboratory?

1. Introduction of a new analyte to the test repertoire
2. Change of analytic methodology
3. Change in patient population

What is a medical decision level?

A specific analyte concentration or value that represents the threshold between different therapeutic approaches.

What is a therapeutic range?

A reference interval applied specifically to monitor a therapeutic drug.

What are the three main clinical categories for applying laboratory reference ranges?

1. Diagnosis of a disease or condition
2. Monitoring of a physiologic condition
3. Monitoring therapeutic drugs

When comparing a test method to a reference method using linear regression, which values confirm agreement without needing new reference ranges?

A correlation coefficient of $1.0$, a slope of $1$, and a $y$-intercept of $0$.

During initial verification using $\ge 20$ specimens, what result permits adopting the reference method interval?

Having $\le 10\%$ of tested specimens fall outside the existing $95\%$ reference interval.

What subsequent action is mandated if $\ge 10\%$ of specimens fall outside the range during both the initial and repeat verification rounds?

The laboratory must evaluate the donor population and initiate a full establishing study with $\ge 120$ individuals.

How do diagnostic sensitivity and diagnostic specificity differ?

Diagnostic sensitivity is the ability of a test to detect a given disease or condition; diagnostic specificity is the ability to correctly identify the absence of a given disease or condition.

What is the distinction between positive predictive value (PPV) and negative predictive value (NPV)?

PPV is the likelihood that an individual has a disease if the test result is abnormal; NPV is the likelihood that an individual is free of disease if the test result falls within the reference interval.