Objectives: To determine anticardiolipin (aCL) and anti-beta(2) glycoprotein I antibodies (anti-beta(2)GPI) in apparently healthy children and express the cut-off levels in concentrations of monoclonal antibodies, and to compare the mean values and frequencies of aCL and anti-beta(2)GPI in children with those in blood donors.
Methods: Blood samples were collected from 29 preschool children and 32 adolescents during their routine preventive follow-up visits. The control group consisted of 52 blood donors. aCL and anti-beta(2)GPI were assayed by an ELISA method. Two monoclonal beta(2)GPI-dependent aCL (HCAL and EY2C9) were used as calibrators.
Results: The estimated cut-off values for immunoglobulin G (IgG) and immunoglobulin M (IgM) aCL, expressed in concentrations of monoclonal antibodies and standardized international units (GPL/MPL units), were 13.9 ng/ml (7.6 GPL) and 33.1 ng/ml (3.3 MPL) for preschool children, 13.5 ng/ml (7.2 GPL) and 36.9 ng/ml (4.0 MPL) for adolescents, and 14.4 ng/ml (8.0 GPL) and 42.6 ng/ml (5.1 MPL) for blood donors. No statistically significant differences in the mean values for IgG and IgM aCL were found between the age groups. The mean value of IgA aCL was significantly higher in blood donors than in preschool children and adolescents (P<0.037 and P<0.025 respectively). Seven (11.4%) of 61 apparently healthy children had low positive values for aCL (IgG for all seven). The estimated cut-off values for IgG and IgM anti-beta(2)GPI were 4.2 and 13.1 ng/ml respectively for preschool children, 3.2 and 13.1 ng/ml for adolescents, and 2.9 and 20.5 ng/ml for blood donors. The mean value for IgG anti-beta(2)GPI was found to be higher in preschool children than in adolescents and blood donors (P<0.0001 and P<0.0001). The mean values for IgM and IgA anti-beta(2)GPI were higher in blood donors than in preschool children (IgM, P<0.007; IgA, P<0.0001) and adolescents (IgM, P<0.01; IgA, P<0.0001). Four (6.6%) of 61 apparently healthy children had positive values for anti-beta(2)GPI (two for IgG and two for IgA).
Conclusions: This is the first report in which the cut-off values for aCL and anti-beta(2)GPI in children are expressed in concentrations of monoclonal antibodies. Low titres of aCL, which were identified frequently in apparently healthy children, were hypothesized to be the result of previous infections. The high mean value of IgG anti-beta(2)GPI observed in preschool children was an unexpected result of the study and might indicate a default response to nutritional exposure to beta(2)GPI in this age group.