Conversion of IgM to IgG by Lysates of Burkitt’s Lymphoma Cells

The important landmark results of [1] showed that the IgM pentamer is an asymmetrical pentagon with an open groove that binds specific (AIM) protein. It contains one large gap. Other proteins could also bind in this way, perhaps leading to the evolution of single, ie. IgG, species. Here we examined the effects on IgM of protein and cell lysates of a leukemic cell line, CRL-1647. Lysates from 1.5 X l 08 cells were fractionated on Sepharose. The different size fractions were incubated with exogenous IgM to determine which ones could release immunopositive species, determined in Western blot analysis. IgG like proteins ~150 kDa and immunoreactive to IgG were released by fractions in the size range of 20 kDa to 5 kDa. When the fractions were incubated without exogenous IgM, IgG release was not found. Some IgG was found in the 150,000 MW size fraction with or without incubation, as expected, because the crude lysates contain endogeous IgG as well as IgM.