Circulating immune complexes in chronic myeloid leukemia: studies on 37 K protein antigen

The 37 K protein, earlier found to be present in 3.75% PEG-precipitates from sera of untreated patients with CML, was further characterized. Gel filtration at neutral pH resolved the PEG-precipitate into a non-IgG containing protein peak-I and a IgG containing peak-II. Immunoprecipitation of peak-II with antihuman IgG antiglobulin and subsequent 2D-SDS-PAGE analysis of the immunoprecipitate revealed the presence of 37 K protein in peak-II confirming its association with IgG. 125I-37 K protein was found to interact with antibodies isolated from autologous and allogenic CML-CIC samples but not with similarly isolated antibodies from normal subject, and patients with AML, ALL, MF, and HD. Peptide maps generated by tryptic digestion of 37 K protein (from five different CML patients) were found to be identical. Specific interaction of 37 K protein with the autologous and allogenic antibodies and identity of peptide maps lead to the conclusion that the 37 K protein is a CML-associated antigen appearing in CIC.