Post‐transfusion purpura associated with alloimmunization against the platelet‐specific antigen, bak^a

Abstract

Post-transfusion purpura (PTP) with severe thrombocytopenia occurred eight days after transfusion in a 28-year-old woman and responded to treatment with prednisone and plasma exchange. In contrast to nearly all previously studied cases of PTP, the patient's platelets were PlA1-positive and anti-PlA1 antibody could not be detected in serum obtained during the thrombocytopenic episode. Her serum was found to contain an antibody specific for a recently described platelet-specific alloantigen, Baka, in addition to multiple HLA-specific antibodies. The patient's platelets, typed following recovery, were Baka-negative. These findings indicate that post-transfusion purpura can occur in association with alloimmunization to platelet-specific antigens other than PlA1. In performing the serologic studies, a close relationship and possible identity between Baka and another recently reported platelet antigen, Leka, was observed. A method for analyzing mixtures of cytotoxic platelet-reactive antibodies without separating the individual antibodies is described.

Post-Transfusion Purpura Associated with Anti-Bak^a and Anti-Pl^A2 Platelet Antibodies and Delayed Haemolytic Transfusion Reaction

“…This patient is unique in having both anti-Baka and anti-PlA2 antibodies; only 2 other patients with anti-Baka have been reported [4,6], 1 of them was originally described as anti-Leka [4], and 2 other patients with anti-PlA2 [7], Although HLA antibodies may be present, as in the case described here, their role in causing PTP is uncertain and a platelet-specific antibody cannot be excluded unless exhaustive tests, such as the chloroquine modification of the PIFT [14] or an immunoblotting technique [15], are carried out.…”

“…Occasional cases of PTP have been reported in P1A1 -positive individuals; in 4 cases the antibody spec ificity has been identified -in 1 as anti-Leka [4], which subsequently appears to be the same as anti-Baka [5], another anti-Baka [6] and 2 anti-PlA2 [7],…”

Efficacy of HPA‐1a (PlA1)‐negative platelets in a patient with post‐transfusion purpura

“…Plasmapheresis is also effective [16,[28][29][30][31][32][33][34][35]. However, when a patient is bleeding, as is frequently the case with PTP, a strategy for immediately improving the platelet count is invaluable.…”

“…Most patients who develop PTP are homozygous for HPA-1b and develop antibodies to HPA-1a [12,13], although other platelet antigens have been implicated [14][15][16][17][18][19]. PTP is associated with an anamnestic response, developing in patients with prior to exposure to an alloantigen via pregnancy or transfusion [12,13].…”

“…IVIg is considered first-line therapy, with one or two doses (0.4 mg/kg) resulting in improved platelet counts within a few days [21,23,24,26]. Plasmapheresis is an important component of therapy Contract grant sponsor: NIH/NCI; Contract grant number: T32-CA-009679; Contract grant sponsor: NIH/NHLBI; Contract grant number: HL-54500 [16,[28][29][30][31][32][33][34][35], but it may be second to IVIg because of its relative unavailability and the risk of necessitating an invasive procedure [34]. High-dose methylprednisolone is of uncertain efficacy [24,36].…”