Circulating group II phospholipase A₂ activity and antilipocortin antibodies in systemic lupus erythematosus. Correlative study with disease activity

Objective. Lipocortin (LC) and phospholipase A₂ (PLA₂) are involved in phospholipid metabolism, and on the cellular level LC seems to be an antagonist of PLA₂. Since anti-LCI autoantibodies were found in systemic lupus erythematosus (SLE), we undertook a study of the relationship between PLA₂, anti-LCI, and disease activity in a large group of patients with SLE. Methods. Sera from 81 patients with SLE were tested for the activity of extracellular PLA₂ and the presence and level of antilipocortin 1 [anti-LCI (IgM) and anti-LCI (IgG)] antibodies. Both were compared to SLE activity. Results. Mean PLA₂ activity was 4.6-fold higher in patients with SLE than in healthy controls (707 ± 219 vs 154 ± 6 u/ml, p < 0.01). PLA₂ activity correlated significantly with PLA₂ immunoreactivity as estimated by an ELISA method using monoclonal antibodies against 'synovial type' PLA₂ (n = 21, r = 0.984, p < 0.001). Anti-LCI IgM and IgG antibody levels were significantly higher in SLE than in healthy individuals [anti-LCI (IgM) 54.5 ± 4.6 vs 22.6 ± 2.3 EU/ml, p < 0.001 and anti-LCI (IgG) 54.3 ± 3.4 vs 22.9 ± 2.3 EU/ml, p < 0.001]. There was no correlation between PLA₂ activity and anti-LCI antibody titers. Elevated levels of PLA₂ [> normal mean + 2 SD (i.e., > 300 u/ml)] were found in 41/81 patients with SLE. Anti-LCI antibody titers were high (> 64 EU/ml) in 23/41 patients: 14/40 patients with SLE with normal PLA₂ (< 300 u/ml) also had higher titers of anti-LCI antibodies. PLA₂ activity was significantly associated with the presence of synovitis, being markedly increased in 11/12 patients. Mean PLA₂ in this group of patients (1593 ± 957 u/ml) was significantly higher (p < 0.001) than that (553 ± 188 u/ml) in the group of 69 patients with SLE without synovitis. Conclusions. There was no correlation of PLA₂ activity with the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) or the Lupus Activity Criteria Count (LACC). Circulating PLA₂ activity in SLE correlated only with active synovitis. There was no correlation of anti-LCI titers with duration of the disease, age, steroid dosage, SLEDAI, or LACC or any individual clinical or laboratory variable included in the assessment of SLEDAI and LACC.