Untitled

Abstract

Preformed donor-specific antibodies against human leukocyte antigen can induce antibody-mediated rejection after organ transplant. Hence, future transplant recipients undergo pretransplant screening for preformed antibodies (ie, virtual crossmatch). Subsequently, prospective (analytic) crossmatching is performed using conventional, complementdependent cytotoxicity assays and/or flow cytometrybased methods. The present article reviews factors that must be considered when unexpected, positive, prospective crossmatches are observed. First, the prozone effect caused by the interference of complement or immunoglobulin M must be abrogated by treating the serum with moderate heat, dilution, hypotonic dialysis, EDTA, or dithiothreitol. Second, the physician must check for the presence of potentially interfering autoantibodies (in a context of autoimmune disease or human immunodeficiency virus infection) or therapeutic antibodies (such as rituximab and antithymocyte globulin). In conclusion, knowledge of each assay's technical characteristics will enable the physician to reliably interpret any discrepancies. The reasons for an unexpected, positive, prospective crossmatch must be elucidated before transplant to ensure efficient organ allocation and optimize patient outcomes.

Aspectos técnicos y clínicos de la prueba cruzada de histocompatibilidad en el trasplante de órganos sólidos

“…Si bien la FCXM es un método con excelente sensibilidad y especificidad, también comparte varios de los problemas asociados a las pruebas celulares (24,37,38). Entre los problemas más importantes, podemos mencionar la unión inespecífica de las inmunoglobulinas a los FcR, los autoanticuerpos no HLA y el uso de anticuerpos terapéuticos para inducción de la inmunosupresión, como rituximab (anti-CD20), daclizumab (anti-CD25), alemtuzumab (anti-CD52) y globulina antitimocítica, que dan lugar a resultados falsos positivos (39)(40)(41)(42)(43).…”

Improved flow cytometry crossmatching in kidney transplantation

“…According to this, background FC-XM reactivity is higher in tests with B lymphocytes than in tests with T lymphocytes, partly because of nonspecific immunoglobulin binding by Fc receptors and surface immunoglobulins on the surface of B cells, as well as other Abs reacting with lymphocytes. Other substances present in the recipient's serum can also bind to Fc receptors (eg, auto-Abs) 8,22 or may target lymphocytes (eg, therapeutic Abs) 8,23 ( Figure 2). False-positive XM may therefore be caused by autoimmune disease.…”

“…7 FC-XM assay is therefore the most sensitive cell-based method for detecting DSAs. However, inconsistencies between virtual-XM (the donor's HLA genotype is compared with the recipient's anti-HLA Ab specificity assessed prior to transplantation in a single-antigen flow bead assay or a phenotype panel bead assay) and FC-XM are not uncommon and the clinical pathologist must understand and explain these discrepancies, 8,9 as the use of FC-XM and single antigen beads assays are still limited by methodological and clinical variations. Especially, DSA strength correlates with CDC-and FC-XM results [10][11][12] or denatured class I HLA antibodies, detected by single antigen beads assays, provide negative XM.…”

“…Like CDC-XM, FC-XM also detects patient allo-and auto-Abs (and not just DSAs) bound to donor cells. Pretest factors associated with a donor's medical care can affect test results by changing the number, viability and target on lymphocytes (such as rituximab on CD20 + B-cells) 8 and the levels of HLA antigen expression (such as statin therapy for hypercholesterolemia, as statins are considered to be immunomodulatory agents). 14 Assay adjustment can be performed to improve the sensitivity and specificity of FC-XM.…”