V. Regnault

Divalent Cations Differentially Regulate Integrin αIIb Cytoplasmic Tail Binding to β3 and to Calcium- and Integrin-binding Protein

We have used recombinant or synthetic αIIb and β3 integrin cytoplasmic peptides to study their in vitro complexation and ligand binding capacity by surface plasmon resonance. α·β heterodimerization occurred in a 1:1 stoichiometry with a weakK D in the micromolar range. Divalent cations were not required for this association but stabilized the α·β complex by decreasing the dissociation rate. α·β complexation was impaired by the R995A substitution or the KVGFFKR deletion in αIIb but not by the β3 S752P mutation. Recombinant calcium- and integrin-binding protein (CIB), an αIIb-specific ligand, bound to the αIIbcytoplasmic peptide in a Ca2+- or Mn2+-independent, one-to-one reaction with aK D value of 12 μm. In contrast,in vitro liquid phase binding of CIB to intact αIIbβ3 occurred preferentially with Mn2+-activated αIIbβ3conformers, as demonstrated by enhanced coimmunoprecipitation of CIB with PAC-1-captured Mn2+-activated αIIbβ3, suggesting that Mn2+activation of intact αIIbβ3 induces the exposure of a CIB-binding site, spontaneously exposed by the free αIIb peptide. Since CIB did not stimulate PAC-1 binding to inactive αIIbβ3 nor prevented activated αIIbβ3 occupancy by PAC-1, we conclude that CIB does not regulate αIIbβ3 inside-out signaling, but rather is involved in an αIIbβ3 post-receptor occupancy event.

Both kinetic data and epitope mapping provide clues for understanding the anti‐coagulant effect of five murine monoclonal antibodies to human β2‐glycoprotein I

The interaction between five murine monoclonal antibodies (mAb) and β2‐glycoprotein I (β2GPI) in the absence of phospholipids was studied using surface plasmon resonance‐based biosensor technology. Two separate epitope regions were confirmed for the five mAb but epitopes of two mAb were shown to be overlapping but not identical. The characteristics of binding on both immobilized β2GPI, using different chemistries of coupling to a dextran matrix and antibody surfaces prepared by two strategies of immobilization, were compared. Binding was strongly influenced by the orientation of the immobilized partner, and the five mAb showed heterogeneity in their binding to immobilized and soluble β2GPI. The observed stoichiometries of mAb‐β2GPI complexes and the detailed analysis of the kinetics of the association and dissociation phases of the interactions with soluble and immobilized β2GPI revealed differences in the dissociation rate constants, resulting in a 10‐fold higher affinity for immobilized β2GPI compared to soluble β2GPI for four out of five mAb. This suggests bivalent binding of these mAb to immobilized β2GPI. In addition, the kinetic data helped explain the differing anti‐coagulant properties of these mAb.

Increased Risk for Heart Valve Disease Associated With Antiphospholipid Antibodies in Patients With Systemic Lupus Erythematosus

Background— Heart valve disease (HVD) is frequent in patients with systemic lupus erythematosus (SLE), and the role of antiphospholipid antibodies (aPL) is controversial. Thus, our objective was to estimate the risk of HVD, including Libman-Sacks endocarditis, associated with aPL in patients with SLE. Methods and Results— Studies were selected if they investigated the association between aPL and HVD in SLE patients and if aPL-negative patients were included for comparison. Data sources were MEDLINE, Embase, Cochrane Library, hand search, contact with investigators, and reference lists of studies, without language restrictions. Data on study and patient characteristics, risk estimates, and study quality were independently extracted by 2 investigators. Pooled effect estimates were obtained by using the DerSimonian-Laird method. Of 234 identified abstracts, 23 primary studies (15 cross-sectional, 7 cohort, 1 case-control) met inclusion criteria, including 1656 SLE patients and 508 cases of HVD. Compared with SLE patients without aPL (n=988), the overall pooled odds ratios for HVD and Libman-Sacks endocarditis in aPL-positive patients (n=668) were 3.13 (95% confidence interval, 2.31 to 4.24) and 3.51 (95% confidence interval, 1.93 to 6.38), respectively. The risk of HVD depending on aPL subtypes was the highest for lupus anticoagulant at 5.88 (95% confidence interval, 2.92 to 11.84) and IgG anticardiolipin antibodies at 5.63 (95% confidence interval, 3.53 to 8.97). Conclusions— Overall, the presence of aPL in SLE patients is significantly associated with an increased risk for HVD including Libman-Sacks endocarditis. The risk conferred by IgG anticardiolipin antibodies is as strong as by lupus anticoagulant. Systematic echocardiographic examinations in SLE patients with aPL should be performed.

Increased Risk for Heart Valve Disease Associated With Antiphospholipid Antibodies in Patients With Systemic Lupus ErythematosusClinical Perspective: Meta-Analysis of Echocardiographic Studies

Background— Heart valve disease (HVD) is frequent in patients with systemic lupus erythematosus (SLE), and the role of antiphospholipid antibodies (aPL) is controversial. Thus, our objective was to estimate the risk of HVD, including Libman-Sacks endocarditis, associated with aPL in patients with SLE. Methods and Results— Studies were selected if they investigated the association between aPL and HVD in SLE patients and if aPL-negative patients were included for comparison. Data sources were MEDLINE, Embase, Cochrane Library, hand search, contact with investigators, and reference lists of studies, without language restrictions. Data on study and patient characteristics, risk estimates, and study quality were independently extracted by 2 investigators. Pooled effect estimates were obtained by using the DerSimonian-Laird method. Of 234 identified abstracts, 23 primary studies (15 cross-sectional, 7 cohort, 1 case-control) met inclusion criteria, including 1656 SLE patients and 508 cases of HVD. Compared with SLE patients without aPL (n=988), the overall pooled odds ratios for HVD and Libman-Sacks endocarditis in aPL-positive patients (n=668) were 3.13 (95% confidence interval, 2.31 to 4.24) and 3.51 (95% confidence interval, 1.93 to 6.38), respectively. The risk of HVD depending on aPL subtypes was the highest for lupus anticoagulant at 5.88 (95% confidence interval, 2.92 to 11.84) and IgG anticardiolipin antibodies at 5.63 (95% confidence interval, 3.53 to 8.97). Conclusions— Overall, the presence of aPL in SLE patients is significantly associated with an increased risk for HVD including Libman-Sacks endocarditis. The risk conferred by IgG anticardiolipin antibodies is as strong as by lupus anticoagulant. Systematic echocardiographic examinations in SLE patients with aPL should be performed.

Increased Risk for Heart Valve Disease Associated With Antiphospholipid Antibodies in Patients With Systemic Lupus ErythematosusClinical Perspective

Background— Heart valve disease (HVD) is frequent in patients with systemic lupus erythematosus (SLE), and the role of antiphospholipid antibodies (aPL) is controversial. Thus, our objective was to estimate the risk of HVD, including Libman-Sacks endocarditis, associated with aPL in patients with SLE. Methods and Results— Studies were selected if they investigated the association between aPL and HVD in SLE patients and if aPL-negative patients were included for comparison. Data sources were MEDLINE, Embase, Cochrane Library, hand search, contact with investigators, and reference lists of studies, without language restrictions. Data on study and patient characteristics, risk estimates, and study quality were independently extracted by 2 investigators. Pooled effect estimates were obtained by using the DerSimonian-Laird method. Of 234 identified abstracts, 23 primary studies (15 cross-sectional, 7 cohort, 1 case-control) met inclusion criteria, including 1656 SLE patients and 508 cases of HVD. Compared with SLE patients without aPL (n=988), the overall pooled odds ratios for HVD and Libman-Sacks endocarditis in aPL-positive patients (n=668) were 3.13 (95% confidence interval, 2.31 to 4.24) and 3.51 (95% confidence interval, 1.93 to 6.38), respectively. The risk of HVD depending on aPL subtypes was the highest for lupus anticoagulant at 5.88 (95% confidence interval, 2.92 to 11.84) and IgG anticardiolipin antibodies at 5.63 (95% confidence interval, 3.53 to 8.97). Conclusions— Overall, the presence of aPL in SLE patients is significantly associated with an increased risk for HVD including Libman-Sacks endocarditis. The risk conferred by IgG anticardiolipin antibodies is as strong as by lupus anticoagulant. Systematic echocardiographic examinations in SLE patients with aPL should be performed.