HLAクラスI抗体が血小板輸血不応状態 (platelet transfusion refractoriness: PTR) に関与することについては数多くの報告があるが, IgM型のHLAクラスI抗体 (IgM-HLA抗体) のPTRへの関与についての報告はほとんどない. そこで, PTR患者121人の凍結保存血清のHLA抗体スクリーニングを, 磁性粒子を用いた Mixed passive hemagglutination assay (M-MPHA) 法, Flow cytometric reagents for detection of panel-reactive antibody against HLA Class I antigens (FlowPRA) 法, Anti-human immunoglobulin lymphocyte cytotoxity test (AHG-LCT) 法により行い, IgM-HLA抗体のPTRへの関与については, 輸血24時間後の補正血小板増加数 (CCI24hours) による血小板輸血効果から推測した. その結果, M-MPHA法により121症例中48症例からIgM-HLA抗体が検出された. 一方, FlowPRA法により検出できたIgM-HLA抗体は, それら48例中35例, AHG-LCT法では20例のみであった. 血小板輸血効果は, IgM-HLA抗体を保有する, 48症例中7症例74輸血において判定できた. IgM-HLA抗体の特異性に対応する抗原を持たない輸血では, CCI24hoursが19.7±4.7(×109/L) を示し輸血効果を得ることができたが, 対応する抗原を持つ輸血では, CCI24hoursが2.0±19(×109/L) を示し輸血効果を得られなかった. PTR患者に高頻度に存在するIgM-HLA抗体は, PTRの原因になると考えられ, その半数以上はAHG-LCT法により検出できなかった. M-MPHAをHLA抗体スクリーニング, 血小板輸血の際の交差試験に用いることで, PTR症例の原因解析と輸血効果の向上に貢献できる可能性がある.

Refractoriness to platelet transfusions is considered one of the major obstacles in treating patients with hematological disorders. Although various transfusion procedures have been tried to prevent HLA alloimmunization, some patients still develop HLA and/or HPA antibodies and become refractory to platelet transfusions. We investigated the AHG-LCT, MPHA, LIFT and FlowPRA methods for detecting HLA antibodies and MPHA using chloroquine-treated platelets for HPA antibodies to analyze immunological factors in platelet transfusion-refractory (PTR) patients. Results showed that HLA antibodies were detected in 55 patients, HPA antibodies in 2 and both HLA and HPA antibodies in 2 patients. HLA-A and -B-compatible platelet transfusions were successful in boosting platelet levels in 27 of the patients. Nine patients developed not only HLA-A and/or -B antibodies but also HLA-C antibodies and became refractory to HLA-A and -B-compatible platelet transfusions. Matching of the HLA-C antigens was required in these patients to ensure the effectiveness of platelet transfusions. In some patients, ABH incompatibility reduced the effectiveness of transfusions. In these patients, platelet crossmatching was useful for predicting platelet survival. Of the 68 ABH-incompatible transfusions evaluated at 24 hours post-transfusion, 20 with positive crossmatches had corrected platelet count increments of 3.1±4.1 (×109)/L. In contrast, 48 transfusions with negative crossmatches had corrected platelet count increments of 18.1±7.6 (×109)/L. Other weak HLA antibodies in ten patients were not detected by the conventional methods but were detected by the FlowPRA method. Owing to screening and crossmatch tests, platelet transfusion efficacy was improved in 59 immunological PTR patients.

We encountered an apheresis donor with a suspected case of mosaicism. The donor, K. A., was a 46-year-old Japanese female registered as an HLA-compatible platelet concentrate (HLA-PCs) donor. In her HLA serological typing for HLA-PCs donor registration, three antigens, HLA-B55, -B61 and -B62, were assigned in the HLA-B locus. She was not a twin and had never undergone transfusion or transplantation. Flow cytometric analysis using platelets and lymphocytes indicated that HLA-B55, -B61 and -B62 antigens were simultaneously expressed on the surface of platelets and lymphocytes. HLA-B allele typing with the polymerase chain reaction restriction fragment length polymorphism technique using genomic DNA from peripheral blood and nails as a somatic sample was carried out to establish HLA-B mosaicism. Three alleles, HLA-B*5502, -B*4002 and B*1501, were assigned in both exon 2 and exon 3. HLA-B mosaicism was observed in both her peripheral blood and nails. The HLA-B*4002 and -B*1501 alleles were inherited by her son, who carried three HLA-B alleles, HLA-B*4002, -B*1501 and -B*4001. No other sign of chimerism or mosaicism was observed in other HLA loci antigens or red cell antigens. These results suggest that this donor has a chimeric allele consisting of a mixture of the nucleotide sequences of HLA-B*4002 and -B*1501 alleles.

BACKGROUND:HLA-C antigens have been thought to be of little significance in determining the efficacy of platelet transfusions. However, six alloimmunized patients were encountered who were refractory to platelet transfusions because of anti-HLA-Cw3, -Cw3, -Cw7, or -Cw8. STUDY DESIGN AND METHODS:Between 1995 and the present, 88 patients with hematologic malignancies became refractory to random-donor platelet transfusions due to HLA antibodies. HLA-A- and HLA-B-compatible platelet transfusions were successful in boosting platelet levels with 82 of the patients. This study concerns the remaining six HLA-immunized patients who were refractory to HLA-A- and HLA-B-compatible platelet transfusions. The response to the platelet transfusions was assessed by calculating both 1- and 24-hour posttransfusion CCIs for each transfusion. RESULTS:The average CCI(1 hour) and CCI(24 hours) in all patients were 20.0 and 12.8 for HLA-A-, HLA-B-, and HLA-C-compatible transfusions and were 1.4 and 1.2 for HLA-A- and HLA-B-compatible but HLA-C-incompatible transfusions, respectively (p < 0.001). CONCLUSION:These findings clearly indicate that matching of the HLA-C antigens is also required in some alloimmunized patients to obtain the effectiveness of platelet transfusions.