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 variousneutralizing 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. Antibodiesagainst IL‐2, IL‐5 and IL‐10 had little or no effect on plaque‐forming cell (PFC) induction; anti‐IL‐6, ‐TNFα and ‐TGFβ enhanced PFC induction; anti‐IL‐1α, ‐IL‐1β, ‐IL‐4, ‐IFNγ 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 thefirst 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 norinduce 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 beenobserved.