Abstract • 145

Introduction: The chronic form of the disease develops in only 15-20% of the cases of ITP in children. Most of these patients have a typical autoimmune disease with production of autoantibodies against platelet surface glycoproteins IIb-IIIa, Ib-IX, Ia-IIa and V. The treatment of these patients is still controversial. We evaluated the possible association of HLA-DR and -DQ antigens in children with the chronic form of ITP.

Patients and methods: 22 girls and 12 boys between the ages of 1 to 18 years (mean age 13,6 years) with chronic form of ITP with detectable antiplatelet antibodies were included in this study. All of them fulfilled the diagnostic criteria for the chronic form of ITP. The platelet count at the time of evaluation of the study was 15-140 ×109/l (mean value 83×109/l). Presence of antiplatelet antibodies of IgG class was tested by direct and indirect monoclonal antibody-specific immobilisation of platelet antigens (MAIPA) and by flow cytometry. For HLA-DRB1* and -DQB1* typing, PCR-SSP technique was used. Healthy donors of blood and/or bone marrow were used as a control group. DRB1* and DQB1* phenotype frequencies of both ITP patients and healthy controls were compared by γ2 analysis with Yates correction.

Results: Antiplatelet antibodies of various types were detected in 30 patients by direct MAIPA technique. In 3 patients we detected antiplatelet antibodies only in the serum. In 1 patient we identified IgM class of PAIg by flow cytometry. We did not prove any association with any DRB1* antigen in our group of ITP patients. We found a decreased frequency of HLA-DQB1*03 (p< 0,05) and an increased frequency HLA-DQB1*02 (p<0,005). All these data remained significant after correction of the p value for the number of antigens tested.

Conclusions: Further collaborative studies are needed for the confirmation of our results and the evaluation of the possible role of DQB1*02 and DQB1*03 in the pathogenesis of ITP.

This project was funded, in parts, by a grant from the IGA, Ministery of Health, the Czech Republic