Cellular immune response to β-glycoprotein-I valine/leucine phenotypes in Mexican patients with primary antiphospholipid syndrome.

Unlabelled: Homozygote genotype V of the β-glycoprotein-I (βGP-I) gene has been associated with anti-βGP-I and thrombosis in patients with primary anti-phospholipid syndrome APS (PAPS). However, the cellular immune response to βGP-I has been little studied.

Objective: To evaluate the immune cellular proliferation in response to native and non-native βGP-I valine/leucine phenotype from Mexican patients with PAPS.

Methods: We studied 10 patients with PAPS and 10 healthy control subjects (HC). The polymorphism at position 247 of the βGP-I gene was determined by PCR-RFLP and the corresponding βGP-I protein was subsequently purified from normal human plasma by affinity chromatography. PBMC purified from patients and controls were stimulated with βGP-I under native and in non native (reduced) conditions. We also determined the anti-βGP-I production in vitro by B cell clones (EBV) generated in cocultures experiments. Differential Scanning Calorimetry (DSC) was studied to determine the structural differences between the βGP-I valine/leucine isoforms. Cytokine profile (IL-2, IL-4, IL-6, TNFα, INFγ) was evaluated in culture supernatants.

Results: PAPS and healthy control PBMCs had a higher proliferative response when stimulated with βGP-I under reduced cultures conditions compared to non-denatured conditions. PBMCs response from PAPS patients was higher. We observed more cell proliferation in response to βGP-I valine/leucine or valine isoforms in non-native conditions. In contrast, this response was not significant against βGP-I leucine. These findings were T CD4-dependent. Similar results were obtained with B cell clones derived from PAPS patients, which showed more pronounced proliferation in non native conditions and higher against βGP-I valine. No differences were found in anti-βGP-I production, but high levels of IL-6 in vitro were identified. The structural analysis of both βGP-I isoforms by DSC showed a major conformational change due to a single mutation in the βGP-I variants.

Conclusions: PAPS PBMCs had a higher cellular response against βGP-I in non-native culture conditions preferentially to the βGP-I valine phenotype. This effect is T CD4 dependent and appears to be driven by tertiary structural changes adopted by βGP-I polymorphism.