Management „falsch positiver“ xMAP-Antikörperbefunde bei der Bestimmung von HLA-Antikörpern

Zusammenfassung

Die Befundung von Luminex®-Tests erfordert neben der Erfahrung in der HLA-Antikörper- (HLA-Ak-)Diagnostik auch die Berücksichtigung technischer Besonderheiten der Luminex®-Technologie. Das betrifft zum einen die Erkennung „falsch positiver“ Reaktionen, die bedingt sein können durch 1) allelspezifische HLA-Ak, 2) HLA-Ak gegen die α- und/oder β-Ketten der HLA-Klasse-II-Moleküle, 3) natürliche kreuzreagierende Antikörper aus Immunisierungen mit Mikroorganismen oder 4) die Denaturierung der HLA-Antigene auf den Luminex®-Beads. Zum anderen betrifft es die Erkennung „falsch negativer“ Reaktionen. Ursachen dafür können 1) Hemmungen der Antigen-/Antikörperbindung in hochtitrigen Seren (Prozonenphänomen), 2) Blockierungen durch HLA-IgM-Ak oder 3) durch Komplementkomponenten sein. Es sind zudem technisch bedingte Unterschiede durch die Auswahl und Dichte der HLA-Moleküle auf den Beads zwischen den verfügbaren Testformaten zu bedenken. Dieses Phänomen kann auch zwischen Beads mit unterschiedlicher HLA-Spezifität innerhalb desselben Testformats beobachtet werden. In jedem Falle müssen zur Plausibilitätsprüfung alle Informationen über Immunisierungsereignisse beim Patienten sowie die Ergebnisse aus einer Stufendiagnostik mehrerer Tests (LCT und Festphasentests) und Testformate (Luminex-Screening, -PRA und -Single Antigen) berücksichtigt werden.

Abstract

The interpretation of Luminex® tests requires comprehensive experience in HLA-antibody diagnostics. Additionally, the consideration of special technical characteristics of this technology is a prerequisite for reporting correct specificities. On the one hand, “false positive” results have to be excluded. These reactions are caused by 1) the reaction of allel specific HLA-antibodies, 2) reactions to the α- and/or β-chains of the HLA molecule, 3) the occurrence of natural antibodies, caused by cross reactivity with bacterial or viral microorganisms or 4) conformational changes of the HLA-antigens fixed on the beadsʼ surface. On the other hand, “false negative” results have to be excluded which might be caused by 1) sera with high antibody titer, 2) blocking by HLA-IgM antibodies or 3) by the complement component C1. Moreover, the differences in the sensitivity of the available test formats with different antigen densities on the beadsʼ surface need to be considered. This phenomenon could also be observed between beads with different specificities within the same test format. In any case, the history of immunizing events of the patient and the history of all performed tests and test formats have to be considered for the final result.

Schlüsselwörter

HLA-Antikörper - natürliche HLA-Antikörper - Luminex®-Technologie - Bead-Array-Technik - Single-Antigen-Beads - Prozonenphänomen

Key words

HLA antibody - natural HLA antibody - Luminex® technology - bead array technique - single antigen beads - prozone phenomenon

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