Avidity of anti-phospholipid antibodies in relation to their levels

Abstract

Introduction: The heterogeneity of anti-phospholipid antibodies can be manifested not only in different antigenic specificities, but also in their avidities. The aim of the study was to investigate the relationship between anti-cardiolipin antibody (aCL) IgG avidities and levels within the range of their titres, from very low to high ones.

Material and methods: We analyzed 78 serum samples from 60 patients by ELISA with chaotropic agents, using urea concentration of 6 and 8 mol/l and single diluted serum samples. The changes of aCL levels and avidities were explored during a long-term follow-up in 14 patients.

Results: The avidities of aCLs did not differ in the groups of patients classified according to aCL levels. The higher avidity antibodies predominated in our patients and the fluctuation of avidities in the longitudinal follow-up did not show significant differences. No relationship between aCL levels and their avidities was found.

Conclusions: aCL avidities seem to have no relationship with aCL levels and high-avidity aCLs; the potentially deleterious effects might be present also in patients with low and extremely low aCL levels. Avidity of aCLs belongs to stable characteristics with insignificant changes in time.

Keywords: ELISA; anti-cardiolipin antibodies; anti-phospholipid antibodies; avidity; chaotropic agents; systemic lupus erythematosus; thrombosis; urea.

Fig. 1

aCL IgG avidities in the groups of patients classified according to aCL titre (very low titre aCL < 10 GPL, n = 30; low titre aCL 10-40 GPL, n = 17; medium-high titre aCL > 40 GPL, n = 13). No significant difference was found among groups regardless of urea concentration used for avidity determination. The central box represents the values from the lower to upper quartile (25th to 75th percentile). The median is shown as the middle line. Outside and far out values are displayed as separate points.

Fig. 2

Dynamics of aCL IgG titres and avidities in 14 patients during follow-up. A) Changes in aCL IgG levels; B) Changes of aCL IgG avidities using 6 mol/l urea for avidity determination; C) Changes of aCL IgG avidities using 8 mol/l urea for avidity determination. Neither aCL IgG levels, nor their avidities determined by 6 mol/l urea as well as 8 mol/l urea significantly differ during follow-up

Fig. 3

Longitudinal follow-up of aCL IgG avidities and titres of in three patients. A) Patient A (female, 30 years old at the first blood sampling) was monitored for immunodeficiency; B) and C) two other patients were treated for systemic lupus erythematosus (B: male, 46 years old at the first blood sampling; C: male, 41 years old at the first blood sampling) (aCL – anti-cardiolipin antibody, AI – avidity index, GPL – standardized international units)