The detection of anti-granulocyte antibodies by chemiluminescence

Kidney transplant outcomes in patients with antibodies to human neutrophil antigen 3a

BACKGROUND

Antibody mediated rejection (ABMR) of kidney transplants has been shown to occur in the absence of a known donor specific antibody to human leucocyte antigen (HLA). Antibodies to the human neutrophil antigen (HNA) system have been detected in kidney transplant recipients and linked to ABMR in the absence of an HLA donor specific antibody (DSA), but there remains limited literature regarding this.

METHODS

Case series analysis was carried out examining three cases of HNA-3a antibody positive flow cytometry cross match (FC-XM) from two transplant centres in Scotland.

RESULTS

All patients included were female and had been sensitised as a result of pregnancy. One live donor recipient with HNA-3a antibodies identified prior to transplant received ATG induction and has had a good outcome. The remaining two patients received deceased donor transplants. HNA-3a antibodies were indicated following a retrospective flow cytometry crossmatch. Both patients received Basiliximab induction and both have experienced ABMR requiring supplementary immunosuppression.

CONCLUSIONS

The predicted rate of HNA-3a antibodies amongst patients awaiting kidney transplant in the UK is <1%. However, with increasing evidence to support a role for HNA-3a antibodies in the development of ABMR there may be value in screening at risk groups to allow for augmented immunosuppression to be considered at the time of kidney transplant.

Human neutrophil antigens: Nature, clinical significance and detection

Granulocytes are an essential part of both the innate and adaptive immune systems. Human neutrophil antigens (HNAs) are a family of epitopes that are located on glycoproteins that are mostly expressed on human granulocytes. Antibodies that recognize these epitopes have been associated with neutropenia, transfusion complications, haematopoietic stem cell transplant nonengraftment and renal transplant rejection. Currently, there are fourteen recognized HNA alleles across five antigen systems (HNA-1 through HNA-5), the molecular basis of which are located on the genes FCGR3B, CD177, SLC44A2, ITGAM and ITGAL, respectively. Elucidation of the associated genes has permitted the development of testing strategies for HNA typing and aided understanding of the associated epitopes. This review will outline the associated clinical conditions that require HNA investigation and how these are performed in specialized laboratories. Investigations provided are both reactive for patients with a variety of existing or suspected neutropenias and proactive in the testing of blood component donors in order to reduce the potential risk to patients who require transfusion.

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.

Leucocyte activation by anti-lactoferrin antibodies bound to vascular endothelium

Human polymorphonuclear neutrophil leucocytes (PMNL) prestimulated with the formylated tripeptide f-Met-Leu-Phe (fMLP) were activated to an immediate chemiluminescence (CL) response by polyclonal rabbit antibodies against human lactoferrin (Lf). This activation, indicating the formation of reactive oxygen species, was induced by intact IgG antibodies but could not be brought about by F(ab')2 fragments. Human Lf was also shown to adhere to the surface of cultured bovine aorta endothelial cells (BEC). When Lf-coated BEC grown on microcarrier beads were reacted with anti-Lf antibodies, an immediate CL response was achieved also with nonprimed PMNL. Here, too, the reaction required intact IgG antibodies. Also, patient sera containing anti-Lf autoantibodies of IgG class were shown to activate fMLP-treated PMNL. The same effect was obtained (in a dose-dependent manner) with the gammaglobulin fraction from anti-Lf-positive serum. Further, anti-Lf-antibody-positive patient sera incubated with Lf-coated BEC beads were also able to activate non-stimulated PMNL to a chemiluminescence response. The results are discussed in relation to possible mechanisms of cell/tissue damage induced by anti-neutrophil cytoplasmic antibodies (ANCA).

Prospective evaluation of the chemiluminescence test for the detection of granulocyte antibodies: comparison with the granulocyte immunofluorescence test

A series of 213 neutropenic patients were tested for the presence of granulocyte antibodies using the granulocyte chemiluminescence test (GCLT) and the granulocyte immunofluorescence test (GIFT). Sera containing lymphocyte (HLA) antibodies were excluded from the study. A direct GIFT was performed on granulocytes from 56 patients. Samples were obtained from patients with a range of clinical conditions including primary adult autoimmune neutropenia, autoimmune neutropenia of infancy, autoimmune neutropenia secondary to Felty's syndrome, rheumatoid arthritis, idiopathic thrombocytopenic purpura, systemic lupus erythematosus, proliferative disorders, bone marrow transplantation and patients with documented febrile or pulmonary transfusion reactions. Overall, granulocyte antibodies were detected in 52.1% of patient sera. Results for the GCLT and GIFT (IgG) were strongly correlated (p < 0.001) for both primary and secondary immune neutropenias. The results confirm the applicability of the GCLT in the granulocyte serology laboratory.

Evaluation of the mechanisms of antiepileptic drug-related chronic leukopenia

Antiepileptic drug (AED)-related chronic leukopenia [white blood cell (WBC) count < 4,000/microliters] is a dilemma, especially when the AED is effective in controlling seizures. We evaluated the possible mechanisms of leukopenia in 7 patients. Mean WBC count was 3,000/microliters with a mean of 42% polymorphonuclear leukocytes (PMN). The AEDs were carbamazepine (CBZ) alone in 1 patient or CBZ combined with phenytoin (PHT), primidone (PRM), phenobarbital (PB) and/or valproate (VPA) in 5 patients; one patient was receiving PHT only. Bone marrow (BM) aspirates and PMN antibody studies using chemiluminescence were normal. Two liver-spleen scans showed mild relative splenomegaly. After exercise, WBC count (n = 7) increased by 54% (SEM 12%), while the WBC counts in controls (n = 5) increased by 52 +/- 16%. Antinuclear antibodies (Hep-2) were absent in 6 patients and positive (1:160) in 1. PMN adhesion to nylon wool was decreased (54 +/- 10% in patients vs. 80 +/- 5% in controls: n = 13, p < 0.005). Our data, particularly the appropriate WBC response to the stress of exercise, and normal BM examinations suggest that continuation of AED therapy when leukopenia is stable and the percentage of PMN is normal is probably safe. Caution should be used if the absolute PMN count is consistently < 1,000/microliters. BM examinations need not be performed routinely for every patient with neutropenia due to AEDs, especially if the leukopenia fluctuates in the range of 2,000-4,000 cells/microliters.

Autoimmune neutropenia of infancy

AIM

Assessment of the clinical and haematological course of autoimmune neutropenia of infancy (ANI) in a defined childhood population in the south east of Scotland.

METHODS

From January 1986 to February 1991 all children presenting with persistent neutropenia were examined serologically for evidence of antigranulocyte antibodies. The clinical course of those children found to have anti-granulocyte antibodies was then closely monitored.

RESULTS

During the study period five children had serologically confirmed ANI, giving an annual incidence of approximately 1/100,000 in this population. All of these cases followed the classic benign course of the condition. The presenting illnesses were mild, often with superficial skin sepsis and the initial absolute neutrophil count (ANC) ranged from 0.00-0.87 x 10(9)/l. All have remained well with no serious infections. Two children attained a normal ANC after 14 and 24 months respectively, the others currently remain neutropenic.

CONCLUSIONS

Autoimmune neutropenia of infancy is a condition which rests on a serological diagnosis. It follows a chronic benign course and all children eventually attain a normal ANC. The level of antigranulocyte antibody in the serum often begins to wane prior to improvement in the ANC and can give an indication of when recovery will begin to occur.

Late onset immune pancytopenia following bone marrow transplantation

A 17-year-old boy developed autoimmune pancytopenia in the absence of chronic graft-versus-host disease 170 d after allogeneic bone marrow transplantation (BMT) from his HLA identical brother. The anaemia and thrombocytopenia responded to conventional immunosuppressive treatment, but the neutropenia was refractory to this and to splenectomy and subsequent removal of splenic remnant. Following total lymphoid irradiation the neutrophil count rose to low normal levels but thrombocytopenia and anaemia secondary to marrow hypoplasia required transfusion support. Bone marrow function was finally normalized by an additional transfusion of donor marrow without prior immunosuppressive therapy. We conclude that late onset immune pancytopenia post BMT caused by antibodies of probable donor origin may be life threatening in the absence of chronic graft-versus-host disease.

Results of the First International Granulocyte Serology Workshop

Eleven laboratories participated in the First International Workshop of Granulocyte Serology. Participants were asked to identify any granulocyte-reactive antibodies present in 12 human sera distributed as unknown samples. Granulocyte immunofluorescence and granulocyte micro-agglutination were the most commonly used techniques. The incidence of false-positive and false-negative reactions was 15 and 4%, respectively. Most laboratories were able to distinguish between granulocyte-specific and anti-HLA antibodies using platelet absorption. The identification of the specificity of granulocyte-specific antibodies caused the most problems; these were correctly identified on only 57% of occasions.

A chemiluminescence assay for erythrophagocytosis

A luminol-dependent chemiluminescence assay for the assessment of the phagocytosis of erythrocytes sensitized with anti-D IgG immunoglobulin by mononuclear leukocytes is described. The mononuclear leukocytes were obtained by apheresis enriched by centrifugation through a density gradient and stored in liquid nitrogen before use. The total reaction mixture, consisting of mononuclear leukocytes-luminol-erythrocytes (either anti-D IgG sensitized or unsensitized controls) was 500 microliters, light detection was by an LKB 1251 luminometer. Peak luminescence was seen between 35-45 minutes, the reaction being exhausted by 120 minutes. Determination of the reproducibility of the assay gave intra- and inter-assay coefficients of variation of 5% and 13% respectively. We found the chemiluminescent response to be affected by the number of erythrocytes used in the assay and by the composition of the medium in which the cells were resuspended, particularly the pH at the initiation of the assay. We also compared the chemiluminescence assay to a microscopic phagocytic assay and found the results virtually identical. However, the former chemiluminescence assay was much easier to perform, marginally more sensitive, less laborious and eliminated any possibility of subjective error.

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.

Anti-platelet opsonic activity in alloimmune and autoimmune thrombocytopenia

A chemiluminescence technique (CLT) has been developed which measures the interaction between human monocytes and antibody-coated (opsonized) platelets. This technique has an objective end-point, is simple to perform and is of comparable sensitivity to the platelet suspension immunofluorescence test (PSIFT) when used to detect anti-platelet allo-antibodies. In contrast, only 4/20 sera from patients with clinically diagnosed autoimmune thrombocytopenia were opsonic in the CLT, while 8/20 of these same sera bound IgG to platelets in the PSIFT. Only one serum gave positive results in both tests.

Anti-granulocyte opsonic activity in sera from patients with systemic lupus erythematosus

Neutropenia is common in patients with systemic lupus erythematosus (SLE) but mechanisms of cell depletion remain obscure. To investigate the possible autoimmune aetiology of neutropenia in SLE, sera from 31 patients with this disorder were tested for anti-granulocyte activity. Granulocyte-binding immunoglobulins were detected by indirect immunofluorescence, and the ability of patient sera to opsonize granulocytes was determined by measuring the chemiluminescent response of human monocytes to granulocytes sensitized by test sera. Sera from 22 of the 31 patients bound IgG to granulocyte cell membranes and/or to nuclei, but only membrane-binding antibodies opsonized the cells for recognition by monocytes. There was no correlation between neutrophil count and the level of granulocyte-binding IgG as measured by indirect immunofluorescence. In contrast, opsonic activity and neutrophil count were inversely correlated (r = 0.5; P less than 0.05). However, opsonic activity was present in sera from most non-neutropenic patients. In patients with SLE, impaired reticuloendothelial system function may allow sensitized granulocytes to remain in the circulation.

Anti-granulocyte opsonic activity and autoimmune neutropenia

Sera from patients with unexplained neutropenia have been assayed for anti-granulocyte opsonic activity using a chemiluminescence technique which measures the metabolic response of human monocytes to antibody-coated granulocytes. This rapid and simple technique was more sensitive than indirect immunofluorescence in the detection of anti-granulocyte antibodies. Anti-granulocyte opsonic activity was detected in sera from 17 of 31 patients, suggesting that their neutropenia may have had an autoimmune basis. The opsonic activity of five of the 17 sera was increased when granulocytes were sensitized in the presence of fresh serum. Four of these sera bound IgM and C3b to granulocytes in the immunofluorescence test. Human IgG when added to the monocyte suspension medium inhibited monocyte response to IgG antibody-opsonized granulocytes. This inhibition was less when granulocytes were opsonized with sera containing IgM and complement granulocyte-binding activity. This observation may be relevant to the selection of neutropenic patients for therapeutic use of intravenous immunoglobulin.