B-CLL cells inhibit Ig secretion by autologous BM cells.

(A) BM cells from patients with CLL (10⁶ cells/mL) were cultured alone or in combination with autologous B-CLL cells (10⁶ cells/mL), either nonstimulated or PMA-induced. At the end of the 7-day culture period, cell-free supernatants were collected and their content in IgG determined by ELISA. The values were expressed as the percentage of control IgG production (BM cells cultured alone). Results are expressed as the mean ± SEM of 36 different patients. Control IgG production in these experiments was 236 ± 72 ng/mL (mean ± SD; n = 36). Purified B-CLL cells cultured alone produced less than 5 ng/mL of either Ig isotype. (B) Effect of adding increasing numbers of PMA-induced B-CLL cells on the IgG-secreting capacity of autologous BM cells (10⁶ cells/mL). Results of one representative experiment are shown. (C) Cellular mechanism involved in this phenomenon. BM cells were cultured alone and in combination with PMA-induced autologous B-CLL cells, either allowing or preventing the contact between the 2 kinds of cells. IgG secreted into the supernatants during 7 days of culture period was determined by ELISA. The values were expressed as the percentage of control IgG production (BM cells cultured alone). Results are expressed as the mean ± SEM of 12 different patients. Control IgG production in these experiments was 443 ± 68 ng/mL (mean ± SEM; n = 12).