Antiphosphatidylethanolamine antibodies as the only antiphospholipid antibodies detected by ELISA. II. Kininogen reactivity

Abstract

Objective: To study the requirement for serum and for low (LMWK) and high molecular weight kininogen (HMWK) and/or HMWK binding proteins to detect antiphosphatidylethanolamine antibodies (aPE) in ELISA.

Methods: Eighteen patients with aPE (9 IgG and 13 IgM) as the only antiphospholipid antibody (aPL) detected by ELISA were assigned to 4 groups: thromboembolic episodes (TEE) (Group I, n = 6); livedo reticularis (LR) without TEE, (Group II, n = 4); both LR and thrombosis (Group III, n = 4); and systemic lupus erythematosus (SLE) or primary antiphospholipid syndrome (APS) (Group IV, n = 4). All sera were analyzed in ELISA with and without bovine serum and with a purified chromatographic fraction containing LMWK, HMWK, and HMWK binding proteins.

Results: Eleven aPE were serum dependent: mostly IgG (7/9) and some IgM (4/13). Among the 11 serum dependent aPE, all the 7 IgG and 2 IgM were kininogen reactive. Some serum independent IgM were better detected in the absence than in the presence of serum in the ELISA.

Conclusion: In the 18 patients, kininogens and/or HMWK binding proteins served as a "cofactor" significantly more often for aPE IgG than for aPE IgM (p = 0.007). Kininogen dependent aPE Ig were observed more often in patients with LR with or without TEE (6/8) than in those with SLE or primary APS (0/4) but this difference merely tended to significance (p = 0.06). In 2 patients, one with TEE, the other with primary APS, the IgM aPE was dependent on a serum "cofactor" that was not kininogen.