Th1 Polarization of Cytokine and Cytokine Receptor Polymorphisms Affect the Susceptibility and Severity of ITP

Introduction: Immune thrombocytopenia (ITP) is an acquired autoimmune disorder characterized by the production of platelet antibodies, resulting in the destruction of platelets and inhibition of their production. Many cytokine profile study have revealed a clear T helper type1 (Th1) cytokine polarization in chronic ITP patients, using quantitative RT-PCR and flow cytometry method. However, it remains unclear whether genetic factors of Th1/Th2 cytokine and cytokine receptor affect chronic ITP. We investigated the impact of IFN-γ+874T/A, IFN-γ receptor (R) -611G/A, IL-4 -590C/T, and IL-4 receptor (R)a Q576R polymorphisms on the susceptibility and clinical feature of chronic ITP and Th1/Th2 ratio in peripheral blood of ITP patients,

Patients and methods: Genotyping was determined by PCR based technique and direct sequencing. The diagnosis and response criteria of the ITP were defined according to International Working Group criteria. We evaluated Th1/Th2 ratio in peripheral blood of 15 normal donors and 25 ITP patients by intracellular flow cytometry. Intracellular IL-4 (Th2 cytokine) and IFN-γ (Th1 cytokine) production was assessed in CD4+ T lymphocytes activated by phorbol 12-myristate 13-acetate and ionomycin by flow cytometry. This study was approved by the IRB of our hospital.

Results: The platelet count ranged from 1´10⁹/L to 98´10⁹/L with a mean count of 32´10⁹/L at the initial diagnosis. Eighty-three patients (56.1%) had bleeding tendency and 24 patients (16.2%) had severe thrombocytopenia (< 10 ´10⁹/L). Steroid treatment was given to 86 patients (58.1%), and eradication of Helicobacter pylori was performed in 38 patients (25.7%), while splenectomy was performed in only 18 patients (12.2%). As compared to control group, chronic ITP patients had significantly higher frequency of the IL-4R576 non-QQ (low function type) than QQ (high function type) (29.7% vs 15.2%, P<0.05). ITP patients with IL-4-590 CC genotype (low expression type) showed lower platelet counts than those with IL-4-590 non-CC genotype (high expression type) (21±17 X10⁹/mL vs 33±27 X10⁹/mL, p<0.05). ITP patients with IFN-γ+874 non-AA genotype (high expression type) showed lower response rate to steroid treatment than those with IFN-γ+874 AA genotype (low expression type) (76.9% vs 97.5%, p<0.05). We examined the association between Th1/Th2 polymorphisms and Th1/Th2 ratio in both normal donors and ITP patients. Th1/Th2 ratio was not significantly different among IFN-γ+874T/A, IFN-γR -611G/A, IL-4 -590C/T, and IL-4Ra Q576R polymorphisms in normal donors.  In contrast, ITP patients with IL-4Ra576 non-QQ genotype (low function type) had higher tendency of Th1/Th2 ratio compared to IL-4Ra576 QQ genotype (high function type) (111.2±216.1 vs. 20.8±21.6, p = 0.12).

Conclusion: These findings suggested that Th1 polarization of Th1/Th2 cytokine and cytokine receptor polymorphisms affect the susceptibility and severity of chronic ITP. Especially, IL-4Ra576 QQ genotype may be closely associated with the risk of ITP and Th1 polarization.