Expressed immunoglobulin repertoire of LPS-stimulated splenocytes of unimmunized mice as studied by two-dimensional gel electrophoresis

The repertoire of isolated immunoglobulin polypeptide chains synthesized by LPS-stimulated splenic B cells from unimmunized 6 weeks old mice was studied by two-dimensional gel electrophoresis. These B cells formed mainly m heavy chains, while only a small amount of g chains was detected on two-dimensional electrophoregrams. The number and character of spots corresponding to each class and type of H and L chains were analyzed. Most of the detected 52 spots, which corresponded to L chains, were well resolved with clearly defined round boundaries. Six of them belonged to two isotypes of l chains and the rest to the k chain. About 25 clusters corresponded to m chains. They had different appearance from those of L chains and their characteristic elliptic form with prolonged vertical axes indicated the presence of several H chain variants of slightly different length (due probably to the length variations of CDR3 and carbohydrate heterogeneity) in each cluster. The limited number of spots both of H and L chains is explained as being due to restrictions in the expressed repertoire of preimmune splenic B cells, which have no somatic mutations in the immunoglobulin genes. The concept of macrorepertoire (referring to the relatively small number of detected molecular species) and microrepertoire (describing the mutationally altered molecules) is introduced.