Platelet-specific antibodies in HLA-immunized patients receiving chronic platelet support.
BACKGROUND
In HLA-alloimmunized patients, the unexpected failure of HLA-matched platelet transfusions usually raises the suspicion about concomitant platelet-specific antibodies. As the reported frequency of platelet-specific antibodies in multitransfused patients varies widely, the aim of this study was to determine the prevalence of such antibodies in a population of chronic thrombocytopenic patients with HLA antibodies.


METHODS
From 1985 to 1997, 11,777 determinations of HLA antibodies were performed in 1330 hematologic patients receiving chronic platelet support. Fifty-two patients with HLA alloimmunization that lasted more than 1 month were selected. The search for platelet-specific antibodies was performed by using a monoclonal antibody immobilization of platelet antigens assay, thus allowing the identification of platelet-specific antibodies directed against the platelet glycoproteins (GP) Ib/IX, GPIIb/IIIa, and GPIa/IIa. Specificity of the platelet-specific antibodies was further investigated by using a solid-phase assay with chloroquine-treated platelets.


RESULTS
Only 2 (3.8%) of the 52 patients had platelet-specific antibodies. One antibody reacted with an epitope of the GPIIb/IIIa that was present in all the panel platelets, and that probably was an autoantibody. The other was an anti-HPA-5b.


CONCLUSIONS
The prevalence of platelet-specific antibodies in patients with HLA alloimmunization is very small. The search for concomitant platelet-specific antibodies would be indicated only when other causes of refractoriness to HLA-matched platelets are ruled out.
Sanz
C
C
Service of Hemotherapy and Hemostasis, Hospital Clinic, Barcelona, Spain. csanz@clinic.ub.es
Freire
C
C
Alcorta
I
I
Ordinas
A
A
Pereira
A
A
D006680:HLA Antigens / Q000276:immunology*; D006801:Humans; D007114:Immunization; D007518:Isoantibodies / Q000276:immunology; D007519:Isoantigens / Q000276:immunology; D017713:Platelet Transfusion
D006680:HLA Antigens; D007518:Isoantibodies; D007519:Isoantigens