The Impact of Human Platelet Antigen Allele on Antiplatelet Antibodies and Cryoglobulins in Patients with Primary Immune Thrombocytopenia and Hepatitis C Virus-Associated Immune Thrombocytopenia.

Background And Objectives: Human platelet antigens (HPAs) are alloantigens associated with antiplatelet alloantibodies and the risk of immune thrombocytopenia (ITP). However, few studies have investigated associations among HPAs, antiplatelet autoantibodies, and cryoglobulins.

Methods: We enrolled 43 patients with primary ITP, 47 with hepatitis C virus-associated ITP (HCV-ITP), 21 with hepatitis B virus-associated ITP (HBV-ITP), 25 controls with HCV, and 1013 normal controls. We analyzed HPA allele frequencies, including HPA1-6 and 15, antiplatelet antibodies binding to platelet glycoprotein (GP) IIb/IIIa, Ia/IIa, Ib/IX, IV, human leukocyte antigen class I, cryoglobulin IgG/A/M, and their associations with thrombocytopenia.

Results: In the ITP cohort, HPA2ab, rather than HPA2aa, predicted a low platelet count. HPA2b was associated with the risk of developing ITP. HPA15b was correlated with multiple antiplatelet antibodies. In HCV-ITP patients, HPA3b was correlated with anti-GPIIb/IIIa antibodies. HCV-ITP patients with anti-GPIIb/IIIa antibodies had a higher positive rate of cryoglobulin IgG and IgA compared with those without anti-GPIIb/IIIa antibodies. Overlapping detection was also found among other antiplatelet antibodies and cryoglobulins. Like the antiplatelet antibodies, cryoglobulins were associated with clinical thrombocytopenia, implying their close relationship. Finally, we extracted cryoglobulins to confirm the exhibition of cryoglobulin-like antiplatelet antibodies. In contrast, in primary ITP patients, HPA3b was correlated with cryoglobulin IgG/A/M rather than anti-GPIIb/IIIa antibodies.

Conclusion: HPA alleles were associated with antiplatelet autoantibodies and had different impacts in primary ITP and HCV-ITP patients. HCV-ITP was considered to be a symptom of mixed cryoglobulinemia in HCV patients. The pathophysiology may differ between these two groups.