IgG subclasses of the multimammate rat, Mastomys coucha: isolation and characterization of IgG1 and IgG2.

The objective of the study was to characterize the IgG-system of Mastomys coucha and to provide antibodies specific for IgG subclasses of this animal species. Serum proteins binding to protein A at pH 8.0 could be eluted in two distinct peaks at pH 7.5 - 6.2 and pH 5.0 - 3.9. The fractions were analysed by SDS-PAGE and immunoelectrophoresis. Both tests suggested an IgG character of the fractions. Based on their migration behavior in the electric field they were classified as IgG1 (anodic position) and IgG2 (cathodic position). After cleavage of IgG1 and IgG2 with papain, the Fc fragments were isolated by their binding to protein A and used to raise antisera in rabbits. The specificity of these antisera to IgG1 and IgG2 was improved by mutual affinity purification. Subsequently these specific reagents were used for further characterization of IgG1 and IgG2. Thus, affinity chromatography of IgG to protein G allowed a differentiation of IgG1 into two subtypes which either bound to protein G at pH 8.0 or not. In combination with isoelectric focussing and 2-dimensional immunoelectrophoresis the results suggest the occurrence of two and three subtypes of IgG1 (IgG 1a-b) and IgG2 (IgG 2a-c) respectively. A synoptical table of available information on the immunoglobulins of M. coucha including IgM, IgA, IgE and a homocytotropic IgG3 is presented. In addition, serum levels of IgG1 and IgG2 are determined in male and female M. coucha of different ages.