Specificity of anti-phospholipid antibodies in infectious mononucleosis: a role for anti-cofactor protein antibodies

Abstract

The antigen specificity of anti-phospholipid antibodies in infectious mononucleosis (IM) was studied using ELISA for the detection of anti-beta2-glycoprotein I (beta2-GPI), anti-annexin V, anti-protein S and anti-prothrombin antibodies and TLC immunostaining for the detection of anti-phospholipid antibodies. This technique enabled us to look at antibodies reacting to 'pure' phospholipid antigens in the absence of protein contamination. Sera from 46 patients with IM, 18 with systemic lupus erythematosus (SLE), 21 with primary anti-phospholipid antibody syndrome (PAPS), 50 with Helicobacter pylori infection and 30 healthy blood donors were tested. This study highlights anti-phospholipid antibodies in patients with IM as specific 'pure' anti-cardiolipin antibodies, while in PAPS and SLE patients anti-phosphatidylserine and anti-phosphatidylethanolamine antibodies were also found. This investigation also shows that the anti-cardiolipin antibodies found in IM can be present with anti-cofactor protein antibodies. The higher prevalence of anti-cofactor antibodies found in IM sera than in Helicobacter pylori sera may be due to the immunostimulatory effect and/or the polyclonal activation often observed in course of Epstein-Barr virus infection. However, anti-beta2-GPI and, to a lesser extent, anti-prothrombin antibodies occur with a significantly lower prevalence in IM than in PAPS patients. This finding suggests that these antibodies should be regarded as the expression of the broad autoimmune syndrome involving the phospholipid-binding plasma proteins.

Fig. 1

Anti-phospholipid antibody (aPl) pattern in ‘infectious’ and ‘autoimmune’ sera. TLC immunostaining was performed with 2 μg of each phospholipid separated using high performance thin layer chromatography (HPTLC) aluminium-backed silica gel 60 (20 × 20) plates. Sera were diluted 1:100 in 0·5% gelatin/PBS. Horseradish peroxidase-conjugated anti-human IgG detector antibodies were diluted 1:500 in 0·5% gelatin/PBS. The colour reaction was developed by adding sodium nitroprusside. Lane A, reactivity of the serum from a patient with primary anti-phospholipid antibody syndrome (PAPS); lane B, reactivity of the serum from a patient with systemic lupus erythematosus (SLE); lane C, reactivity of the serum from a patient with acute mononucleosis infection; lane D, reactivity of the serum from a patient with Helicobacter pylori infection; lane E, reactivity of the serum from a healthy donor.

Fig. 2

Anti-cofactor protein antibody pattern in ‘infectious’ and ‘autoimmune’ sera. The occurrence of anti-cofactor protein antibodies in infectious mononucleosis (IM), systemic lupus erythematosus (SLE), primary anti-phospholipid antibody syndrome (PAPS), Helicobacter pylori infection patients and healthy blood donors was detected by ELISA.