Abnormal laboratory data due to interaction between immunoglobulins and other serum proteins

Two cases with abnormal laboratory data due to interaction between immunoglobulins and other serum proteins are described. Case 1 was a patient with lactate dehydrogenase (LD) -IgG3 complex whose serum LD value was moderately elevated. Case 2 were nondiabetic patients with IgA type M-proteinemia who had significantly increased serum fructosamine (FRA). The IgG3 in Case 1 was found to be conjugated to LD by immunoprecipitation assay. The LD-IgG3 complex was easily dissociated by affinity chromatography on 5'-AMP or Cibacron Blue F3G-A. The relative molecular weights of the patient's gamma3 chains and light chains were 67,000 and 28,000, respectively, by Western blotting, which corresponded to the expected values. However, the patient's IgG3 did not react to the anti-kappa and anti-lambda light chain antibodies in Immunofixation electrophoresis. Serum FRA concentrations were higher in patients (Case 2) with IgA type M-proteinemia or polyclonal hyper-IgA than those with the IgG type or IgM type. The sera from the patients with IgG or IgM type M-proteinemia had FRA only at the position of albumin, but 11 of 13 sera with IgA type M-proteinemia stained for glycoprotein at the position of the M-protein band as well as the albumin band. The abnormal precipitin arcs of IgA-albumin complex were observed in 11 of 13 sera from patients with IgA type M-proteinemia that were glycosylated at the position of M-protein band.