Detection of a soluble form of BAFF in the sera of B-CLL patients by SELDI-TOF MS. (A) Analysis of the protein G chip after affinity binding of the rabbit anti-BAFF antibody. The expected peak of 155 kDa and the different “echoes” corresponding to increasing degrees of ionization are not shown because only proteins in the range of 15 000-40 000 Da are presented for clarity. The 22-kDa peak corresponds to a contaminating protein in the IgG preparation. (B) Analysis of a recombinant soluble form of BAFF (17 kDa; BioVision) on a golden chip. (C) Analysis of the protein G chip after affinity binding of the anti-BAFF antibody and washing and incubation with the recombinant soluble form of BAFF and washing. (D) Analysis of the protein G chip after affinity binding of the anti-BAFF antibody and washing and incubation without (black) or with (blue) normal sera or B-CLL sera (red) and washing. Recordings corresponding to these 3 analyses have been superimposed. (E) Pseudo gel representation of the previous data with separate records for the control (top), normal sera (middle), and B-CLL sera (bottom).