Association between HLA and red cell antigens. VII. Survival studies of incompatible red blood cells in a patient with HLA-associated haemagglutinins

Human Leucocyte Antigen Sensitisation and Its Impact on Transfusion Practice

Human leucocyte antigen (HLA) sensitisation, including the formation of antibodies against HLA, can cause serious effects in patients receiving blood. Under certain circumstances, donor HLA antibodies in the blood product can trigger the patient's granulocytes to release mediators that cause transfusion-associated lung injury (TRALI), a serious complication of transfusion. The HLA systems of both donor and patient are involved in transfusion-associated graft-versus-host disease, which is a rare disease with a high mortality. Patient HLA antibodies can destroy incompatible platelets and may cause refractoriness to platelet transfusion. Identification of a patient's HLA antibody specificities is necessary for issuing compatible platelets to overcome refractoriness. Many techniques for the detection and identification of HLA antibodies have been developed, including complement-dependent cytotoxicity assay, bead-based assays, the platelet adhesion immunofluorescence test, and the monoclonal antibody-specific immobilisation of platelet antigens assay. Different strategies for the selection of HLA-compatible platelets are applied. These strategies depend on the breadth of antibody reactivity and range from avoiding single HLA antigens in the platelet concentrates issued to apheresis of platelets from HLA-identical donors. The mechanisms of HLA sensitisation and the efforts made to provide compatible blood products to sensitised patients are reviewed in this article from the perspective of clinical transfusion medicine.

HLA alloimmunization is associated with RBC antibodies in multiply transfused patients with sickle cell disease

BACKGROUND

Alloimmunization to minor red blood cell (RBC) antigens occurs commonly in sickle cell disease (SCD). Patients with alloimmunization demonstrate increased risk for new alloantibody formation with subsequent transfusion. Alloimmunization to human leukocyte antigens (HLA) can occur with RBC transfusion and may result in graft rejection during stem cell or organ transplantation. The prevalence and risk factors for HLA alloimmunization in multiply transfused pediatric SCD patients are unknown.

PROCEDURE

A cross-sectional study of HLA alloimmunization in SCD patients aged 3-21 years with a history of >or=3 RBC transfusions was performed to test the hypothesis that HLA alloimmunization is associated with RBC alloimmunization. Antibodies to class I and class II HLA were measured by Flow Panel Reactive Antibody (FlowPRA).

RESULTS

Seventy-three SCD patients (30 with RBC antibodies) were tested. HLA antibodies were detected in 25/73 (34%) patients; class I HLA antibodies occurred in 24/73 (33%) and class II HLA antibodies occurred in 3 (4%). Among patients with RBC antibodies, 16/30 (53%) had HLA antibodies, while 9/43 (21%) patients without RBC antibodies had HLA antibodies (OR 4.32 [1.6-12.1]). In a multivariate analysis, antibodies to RBC antigens were an independent predictor of HLA alloimmunization (P = 0.041). The association of RBC and HLA immunization was strongest among patients with no history of chronic transfusion therapy.

CONCLUSIONS

This analysis is the first description of HLA alloimmunization in pediatric SCD patients who receive primarily leukoreduced RBC transfusions and demonstrates that HLA alloimmunization tendency is associated with antibodies to RBC antigens.

Immune hemolytic anemia associated with negative routine serology

Immune hemolytic anemia can occur in patients who have no antibodies detectable by routine procedures (direct [DAT] and indirect [IAT] antiglobulin tests). DAT-negative autoimmune hemolytic anemias (AIHAs) represent 5% to 10% of all AIHAs. Three causes have been identified: (1) small numbers of red blood cell (RBC)-bound IgG molecules below the threshold of the DAT; (2) IgA and IgM autoantibodies; and (3) low-affinity autoantibodies. Antibody-independent cytotoxic events caused by natural killer (NK) cells have also been implicated. DATs are sometimes found to be positive when tested by reference laboratories, due to poor technique in reading antiglobulin tests in hospital laboratories. Hemolytic transfusion reactions also can occur when no alloantibodies are detectable by routine procedures. In some cases antibodies can be detected by special serologic procedures (such as the Polybrene test); in other instances phenotypically matched RBCs survive well and a specific antigen can be shown to be involved, suggesting a specificity (like anti-C) that is undetectable by any technique. Antibodies other than to blood group antigens, such as human leukocyte antigen (HLA) antibodies, may sometimes be involved.

The clinical significance of HLA antigens on red cells. Survival studies in HLA-sensitized individuals

To investigate the clinical significance of HLA determinants expressed on red cells (RBCs), 51Cr survival studies were carried out in six women (four healthy individuals, two patients with solid carcinoma) immunized against HLA antigens by pregnancy or blood transfusions, respectively. Donors were selected who were compatible in typical RBC antigen systems assayed by conventional techniques but were mismatched for the HLA antigens in question. Crossmatches also were performed with RBC, as well as with lymphocytes, by means of a radioimmune anti-IgG test (RIAT). We found that RBC survival was shortened in all cases. The mean life-span of RBCs depended on antigen specificity rather than on the antibody strength. HLA incompatibility of RBCs could be monitored by the RIAT in all donor/recipient pairs. We conclude that a shortened mean life-span of RBC is to be expected by HLA antibodies, especially when HLA-B7 is involved, but the severity of an in vivo immune reaction in HLA incompatible transfusions cannot be predicted from the in vitro tests used.

Haemolytic transfusion reactions due to HLA antibodies. A prospective study combining red-cell serology with investigations of chromium-51-labelled red-cell kinetics

In a prospective study to see whether HLA sensitisation is associated with increased red-blood-cell (RBC) destruction after HLA-incompatible transfusion, chromium-51-labelled RBC survival and site of sequestration were monitored in nine patients in whom HLA antibodies had developed after RBC transfusions. The donors selected were compatible in ABO and RBC-specific antigen systems but mismatched for the HLA antigen in question. Haemolytic transfusion reactions occurred in all four patients who received HLA-B7-incompatible RBC. A direct radioimmune anti-IgG test became positive, Cr51-RBC survival was very short (22.3, 36.9, 41.4, and 44.0 days), and excess sequestration in the spleen was measured. There was a rise in serum lactic dehydrogenase and a fall in haptoglobin. HLA-B7 antibody was detected in the eluate prepared from RBC collected after transfusion. A similar reaction was found in only one further patient, caused by an HLA-A2 incompatibility. No indications of immune-mediated RBC sequestration were discernible after transfusion of HLA-B7-compatible RBC in one of the patients who had shown a reaction with HLA-B7-incompatible blood, nor in any of the other patients who received HLA-B7-compatible RBC. The haemolytic transfusion reactions could not be anticipated by conventional crossmatch procedures, nor by the measurement of the Cr51-RBC survival 1 h after transfusion.