Stimulation of B cell differentiation by adherent mononuclear cells in systemic lupus erythematosus

We studied B cell proliferation and differentiation in response to factors released by adherent monocytes in patients with systemic lupus erythematosus (SLE). Adherent cell supernatants (ACS) were added to peripheral blood mononuclear cells, and the effects on IgG synthesis, the number of Ig-secreting cells (ISC), and proliferation were determined. Exposure of SLE mononuclear cells to autologous ACS caused an increase (approximately two-fold) in IgG production and ISC numbers. In contrast, exposure of normal mononuclear cells to autologous ACS did not significantly increase IgG production or ISC numbers. Addition of SLE ACS to cultures of normal mononuclear cells did not stimulate ISC production. There was no significant level of 3H-thymidine uptake by cultures of SLE or normal mononuclear cells in response to either SLE or normal ACS. In the presence of an excess number of autologous T cells, ACS stimulation of IgG synthesis was further enhanced. These findings indicate that adherent monocytes contribute to B cell hyperactivity in SLE by stimulating B cell differentiation. SLE mononuclear cells appear to be more responsive to ACS stimulation than are normal mononuclear cells.