Effect of 12 neutralizing anti-cytokine antibodies on in vitro activation of B-cells. Interleukin-12 is required by B1a but not B2 cells.

Normal human peripheral blood mononuclear cells, depleted of most monocytes and virtually all CD8-positive cells, were stimulated in vitro with pokeweed mitogen plus Staphylococcus aureus Cowan I in the presence or absence of various neutralizing anti-cytokine antibodies. Numbers of CD5+ and CD5- immunoglobulin-secreting cells were determined using the protein A haemolytic plaque assay after labelling B1a cells with anti-CD5-coated beads. Antibodies against IL-2, IL-5 and IL-10 had little or no effect on plaque-forming cell (PFC) induction; anti-IL-6, -TNF alpha and -TGF beta enhanced PFC induction; anti-IL-1 alpha, -IL-1 beta, -IL-4, -IFN gamma and -IL-13 suppressed PFC induction. B1a and B2 cells were equally affected by cytokine deprivation using these 11 neutralizing antibodies. In contrast, neutralizing anti-IL-12 suppressed induction of CD5+ but not CD5- PFC. Furthermore, recombinant IL-12, if added during the first 48 h of culture, enhanced CD5+ PFC induction while marginally suppressing (IgG-) or not affecting (IgA-, IgM-) induction of CD5- PFC. IL-12 did not preferentially increase survival in culture of B1a cells nor induce expression of CD5 on B2-cells. Further studies are required to determine whether manipulation of B1a and B2 subsets in vivo using IL-12 could be achieved in clinical situations where imbalances in the two populations have been observed.