Avaliação da agregação plaquetária em presença de anticorpos antifosfolípides: anti-β2GP1 e anticardiolipina

IgG fractions from patients with antiphospholipid syndrome and systemic lupus erythematosus bind to platelets, but do not affect collagen-induced platelet activation

Anti-beta-2 glycoprotein 1 (anti-β2GP1) is an antiphospholipid antibody found in patients with antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE). Its presence commonly is associated with thrombosis; however, the mechanisms of interaction of anti-β2GP1 antibodies and platelets remain unclear. We investigated the effects of APS and SLE patient-derived IgG fractions on collagen-mediated platelet aggregation and examined the binding of patient-derived IgG to platelets before and after activation by collagen. IgG fractions, 150, 200, 300 or 350 µg/ml, isolated from 11 patients with APS and SLE were incubated with two sets of platelet-rich plasma (PRP) in the incubation wells of an aggregometer. The first set was activated by collagen and the other set was incubated for an additional 10 min. All platelets were collected by centrifugation and fixed in cell blocks. We assessed binding of IgG to platelets using immunocytochemistry (ICC). Patient-derived IgG fractions did not affect collagen-induced platelet aggregation. ICC staining using anti-human IgG antibodies demonstrated that patient-derived IgG fractions had greater affinity for non-activated platelets than those activated by 0.75 µg/ml collagen. Patient-derived IgG fractions bound to the surface of platelets and potentially could be internalized by platelets. IgG fractions from APS and SLE patients may sensitize non-activated platelets, which could increase platelet reactivity and thrombotic risk in patients. We did not detect secondary effects of patient-derived IgG fractions.

Effects of Toll-like receptor 4 on β2-glycoprotein I-induced splenic T cell subsets differentiation

Our previous study demonstrated that beta 2-glycoprotein I (β2GPI) stimulation promotes bone marrow derived dendritic cells (BMDCs) maturation and T cell proliferation in a Toll-like receptor 4 (TLR4) dependent manner. However, β2GPI induced T cell differentiation and the role of TLR4 in this process have rarely been reported. In the present study, we focused on the differentiation of splenic T cells in β2GPI immunized Balb/c, C3H/HeN and C3H/HeJ mice. According to our results, Th2 dominated differentiation was observed in β2GPI immunized Balb/c and C3H/HeN mice than in those treated with normal saline (NS), namely the up-regulated levels of Th2 markers GATA3 and IL-4 (p < 0.05). Meanwhile, reduced Th1 markers T-bet and IFN-γ, and Treg marker Foxp3 were observed in β2GPI immunized mice (p < 0.05). C3H/HeJ mice have the same gene background with C3H/HeN mice except a functional mutant in TLR4 gene. However, the described Th2 differentiation was not detected in these TLR4 deficient mice, indicating the importance of TLR4 in immune response against β2GPI. In addition, we found that β2GPI-induced Th2 differentiation could be strengthened by cytokines secreted by dendritic cells (DCs) and DCs-T cells interaction. However, DCs-T cells contact was indispensable during this process because of its unique role in suppressing Th1 function. Furthermore, this Th2 biased differentiation pattern was more noticeable in mice received 4 times β2GPI immunization than those received 2 times, suggesting the amplifying effects of anti-β2GPI Ab on β2GPI induced Th2 response. These findings may partly explain the immune imbalance in APS patient through the view angle of T cell differentiation and anti-β2GPI antibody production.

Further Investigations of the Effects of Anti-β2GP1 Antibodies on Collagen-Induced Platelet Aggregation

Anti-beta-2-glycoprotein 1 (anti-β₂GP1) antibodies are associated with increased thrombotic risk in patients with autoimmune disease. There is conflicting evidence on the effects of anti-β₂GP1 antibodies on platelets, with both enhanced and inhibited aggregation previously reported. However, previous studies did not include isotype antibodies to ensure the observed effects were due to anti-β₂GP1 antibodies. The aims of this study were to (1) investigate the effects of anti-β₂GP1 antibodies on collagen-induced platelet aggregation in parallel with negative control (buffer normal saline) and isotype control antibodies and (2) determine the lupus anticoagulant (LA) activity of anti-β₂GP1 antibodies used. Three animal-derived anti-human-β₂GP1 antibodies (1.25, 2.5, and 5 μg/mL) incubated with healthy platelet-rich plasma were activated by collagen (2.5 μg/mL). Each anti-β₂GP1 antibody demonstrated the inhibition of aggregation compared to negative control, but not to isotype control. No anti-β₂GP1 antibody demonstrated LA activity, suggesting they were probably nonpathological. This study highlights both negative and isotype control markers are important to validate the effects of anti-β₂GP1 antibodies. Assays to measure anti-domain I-β₂GP1 antibodies are recommended to be used in conjunction with functional measures to further investigate the effects of anti-β₂GP1 antibodies.

Identification of anti-moesin antibodies in the serums of patients with antiphospholipid syndrome

INTRODUCTION

The antiphospholipid syndrome (APS) is an acquired autoimmune disease characterized by recurrent vascular thrombosis and obstetric complications. However, the precise mechanisms by which the autoantibodies mediate disease remain to be elucidated. Moesin is an intracellular protein that links the cell membrane and cytoskeleton, mediating the formation of microtubules and cell adhesion sites as well as ruffling of the cell membrane, which is crucial for platelet activation.

MATERIALS AND METHODS

We screened the serums from patients with APS for the presence of anti-moesin antibodies (anti-moesin Abs) recognizing antigens derived from prokaryotic expression system, and investigated the effect of murine monoclonal anti-moesin Abs (anti-moesin mAbs) on platelet activation and aggregation by flow cytometry and platelet aggregation assay in vitro to study their potential pathogenic role in APS.

RESULTS

The presence of anti-amino (N)-terminal portion of moesin antibodies (anti-moesin-N Abs) was observed in 73% (73/100) patients with APS, which was significantly higher than anti-cardiolipin antibodies (aCL, 49%) and anti-β2 glycoprotein I antibodies (anti-β2GPI, 43%). Moreover, the elevated anti-moesin-N Abs levels significantly correlated with plasma levels of anti-β2GPI (rs=0.474, P<0.001) rather than aCL (P=0.203). The murine anti-moesin mAbs promote platelet activation and aggregation in vitro, which could be effectively neutralized by moesin-N.

CONCLUSIONS

In combination of the detection of aCL and anti-β2GPI, screening for the presence of anti-moesin-N Abs might has its value in facilitating the laboratory diagnosis of APS. The pathogenic role of anti-moesin-N Abs in the serums of APS patients needs to be further studied.