Combined search for anti–β2-glycoprotein i and anticardiolipin antibodies in antiphospholipid syndrome: Contribution to diagnosis

Standardized antigen preparation to achieve comparability of anti-beta2-glycoprotein I assays

INTRODUCTION

The Sydney classification for diagnosis of the antiphospholipid syndrome (APS) first introduced the determination of anti-beta2-glycoprotein I (anti-beta2-GPI)-antibodies in serum as laboratory criteria. In this context, widely differing results of anti-beta2-GPI assays are a concerning issue. Considerable efforts have been made to optimize ELISAs, however little attention was hitherto spent to the antigen preparation. We evaluated the influence of different beta2-GPI preparations on the ability to separate ill and healthy patients and on the comparability of anti-beta2-GPI-assays.

MATERIALS AND METHODS

Microplates were coated with various beta2-GPI preparations and anti-beta2-GPI IgG- and IgM-ELISAs were performed for 21 APS patients and 21 controls using the monoclonal calibrators HCAL and EY2C9. Subsequently, by use of a surface plasmon resonance (SPR) biosensor, affinity constants for the HCAL- and EY2C9-interaction with each beta2-GPI preparation were determined and antigen binding of sera of APS patients and controls was studied.

RESULTS

All ss2-GPI preparations showed good discrimination ability ill vs. healthy but poor inter-assay comparability in the ELISAs. Affinity constants for HCAL and EY2C9 were independent of the beta2-GPI variant (K(A) 0.105 - 0.200 and 0.449 - 1.04 x 10(10)M(-1); K(D) 50.0 - 95.5 and 9.61 - 22.3 x 10(-11)M, respectively). In the biosensor, reactivity to the different beta2-GPIs was negligible for the controls and varied considerably for patients.

CONCLUSION

Inter-assay comparability of anti-beta2-GPI ELISAs is highly dependent upon the beta2-GPI preparation. Only agreement on one common beta2-GPI preparation will improve the requested inter-assay comparability.

Étude de l'association hépatite auto-immune et antiphospholipides

INTRODUCTION

Only few series have reported the association of autoimmune hepatitis with antiphospholipid antibodies. The aim of our study is to investigate the frequency of these antibodies in a series of autoimmune hepatitis and to search for a correlation with clinical, biological or histological characteristics.

MATERIAL AND METHODS

Antiphospholipid were investigated in 24 patients with well defined autoimmune hepatitis. Characteristics were compared between antiphopholipids positive and negative patients. Characteristics of our patients were also compared toward cases collected in a literature review.

RESULTS

The frequency of antiphospholipid antibodies is of 70.8% in our series. Four patients had a well defined antiphospholid syndrome. Seven patients had a systemic lupus erythematosus in the antiphospholipid group whereas none in the antiphospholipid negative group. The frequency of the different antiphopholipid antibodies was: IgG ACL (52.9%), IgM APE (52.9%), ACC (43.7%), IgG Abeta2GP1 (41.2%). We found no correlation between hypergammaglobulinemia and the presence or the isotype of antiphospholipid antibodies. Clinical presentation and outcome as biological and histological parameters were similar in both groups.

CONCLUSION

Our study report a high frequency of antiphospholipids antibodies in autoimmune hepatitis patients. However we found no clinical, biological or histological correlation with the presence of antiphospholipids. Further longitudinal studies on larger cohorts should clarify the association between antiphospholipid antibodies and autoimmune hepatitis and potential therapeutic issues.

Can cryoglobulins interfere with the measurement of IgM antiphosphatidylethanolamine antibodies by ELISA?

Clinical manifestations of the antiphospholipid antibody syndrome (APS) have been recently related to the presence of phosphatidylethanolamine antibodies (aPE). However, it is well known that some molecules such as cryoglobulins, immunoglobulins that undergo a reversible precipitation at low temperatures, may interfere with biological assays. With this in view, we report the case of a patient with APS who was positive for both IgM aPE and type III cryoglobulinemia. Moreover, we show for this patient a potential implication of aPE in the cryoprecipitate formation. To further analyze the potential association between cryoglobulins and aPE, and also the possible consequences for aPE assay, we selected 55 patients according to positivity for both IgM aPE and cryoglobulinemia. Determination of IgM aPE levels was made before and after removal of cryoprecipitate from the serum. Of the 55 selected patients, 52 (95%) presented no significant difference for IgM aPE levels before and after cryoprecipitation. These results were ascertained whatever the aPE levels and clinical status of the patient. Taken together, our results indicate that cryoprecipitation does not interfere in most cases (95%) with the dosage of IgM aPE. Thus, IgM aPE do not appear to be involved in the formation of the cryoprecipitate.