Factors Affecting IgA Related Hyperviscosity

Sera from 14 patients with an IgA M-component, six of whom had myelomatosis and eight with benign monoclonal gammopathy (BMG) were analysed. All six sera from patients with high IgA (greater than 40 g/l) and total protein (greater than 100 g/l) concentrations were hyperviscous (HV). Four of these six patients also had hyperviscosity syndrome (HVS). There was no correlation between the quantity of IgA dimers or polymers and the presentation of HV and HVS. The binding between IgA and albumin and alpha 1-anti-trypsin was not covalent. Differences in the microenvironment of S-S bonds or of aromatic amino acids between isolated monoclonal monomeric and dimeric IgA were demonstrated with circular dichroism. Besides that, differences in hydrophobicity (exposure of aromatic amino acids) between IgA from normal serum and monomeric and dimeric IgA from a myeloma serum were revealed using hydrophobic interaction chromatography. The significance of hydrophobic interactions involving IgA and the influence of such forces on the circulation of the molecules are discussed.