Absorption of IgM paraproteins with recombinant P-7. (A) IgM paraprotein with P-7 reactivity and absorption with a P-7 column. (B) IgM paraprotein with non–P-7 reactivity and absorption by a P-7 column (control). (Top) Serum electrophoresis before and after absorption, (bottom) immunofixation before and after absorption with P-7. The absorption studies of 3 sera containing a P-7 reactive IgM paraprotein and 2 IgM control paraproteins with P-7 nonreactivity yielded identical results.