Anti-platelet opsonic activity in alloimmune and autoimmune thrombocytopenia

The use of interferon-gamma-treated U937 cells in chemiluminescence assays to detect red cell, platelet and granulocyte antibodies of potential clinical significance

The chemiluminescent (CL) response of interferon-gamma-treated U937 (IFN-U937) cells to sensitized target cells has been used to detect red cell, platelet and granulocyte antibodies. A clone of U937 cells was selected which expressed Fc receptor I (Fc gamma RI) and which, after incubation with IFN-gamma for 72 h, was capable of generating high levels of lucigenin-enhanced CL. The CL responses of IFN-U937 cells and peripheral blood human monocytes to sensitized red cells, platelets or granulocytes were then compared. Assays using monocytes or IFN-U937 cells were of comparable sensitivity for detection of antibodies against all three types of target cell. In addition, the use of IFN-U937 cells reduced interassay variation and simplified assay performance. The potential clinical usefulness of these CL assays was suggested by the ability of both monocytes and IFN-U937 cells to respond to red cells, platelets or granulocytes sensitized with sera from pregnant women whose babies had either haemolytic disease of the newborn (HDN), alloimmune thrombocytopenia or alloimmune neutropenia respectively. In addition, monocytes and IFN-U937 cells both responded to red cells sensitized with antibodies against a variety of specificities of assumed (although not documented) clinical significance for blood transfusion recipients. In contrast, monocytes and IFN-U937 cells responded only weakly to red cells sensitized with either anti-D in sera from mothers of babies unaffected by HDN, or with antisera containing high titre antibodies with specificities not normally associated with significantly reduced red cell survival.

The chemiluminescent response of human monocytes to red cells sensitized with monoclonal anti-Rh(D) antibodies

Luminol-enhanced chemiluminescence (CL) was used to assess the metabolic response of human monocytes to red cells sensitized with known amounts of anti-Rh(D). Monoclonal antibodies were used to facilitate a comparison between the functional activities of IgG1 and IgG3 subclasses. The detection of CL provided a simple, rapid and semi-quantitative means of measuring monocyte response to sensitized red cells (IgG-RBC). Monocyte response to IgG3-RBC was quantitatively greater, more rapid and less susceptible to inhibition by fluid phase IgG than monocyte response to IgG1-RBC. The minimum levels of sensitization required to elicit CL from monocytes were approximately 2500 IgG3 molecules per red cell, or approximately 5000 IgG1 molecules per cell.

Report of the Platelet and Granulocyte Serology Working Group, 1986

A blind trial conducted amongst 29 laboratories revealed that the overall incidence of 'false-positive' results in tests for anti-platelet antibodies was greater for heat-treated serum and plasma samples than for untreated samples.

A survey of anti-platelet antibody detection--report of the UK Platelet and Granulocyte Serology Working Group, 1985

In 1985, serum samples were distributed to 27 laboratories within the UK and Eire with the objective of determining the current state of anti-platelet antibody detection. The sera included five unknown samples for blind assessment and four well-characterized reference reagents. The laboratories involved used a wide range of different methods but the most commonly used techniques were the fluorescent antiglobulin test and the enzyme-linked immunosorbent assay. In the trial, all responding laboratories were able to detect potent anti-platelet alloantibodies but there was a 43% incidence of 'false positive' results with samples which had been designated as inert. There were no apparent differences in performance between assays using fluorescein- or enzyme-labelled antiglobulin reagents or between assays which utilized PFA-treated rather than untreated platelets.