INDUCTION OF NF-AT IN NORMAL B-LYMPHOCYTES BY ANTIIMMUNOGLOBULIN OR CD40 LIGAND IN CONJUNCTION WITH IL4

We show here that ligation of surface immunoglobulin or CD40 receptors in conjunction with interleukin-4 induces the nuclear factor of activ ated T cells (NF-AT) in normal murine B cells, which is inhibited by c yclosporin (CsA). Lipopolysaccharide, which activates B cells by a Ca2 +-independent, CsA-resistant pathway, does not induce NF-AT. The NF-AT complex in T cells and B cells appears to be identical, comprising bo th Fos and Jun proteins and the 120 kDa cytosolic component of NF-AT ( NF-AT(p)). Our transfection experiments using a trimerized NF-AT site linked to the minimal IL-2 promotor driving luciferase activity demons trate that NF-AT is functional in A20 B-lymphoma cells. These results therefore suggest that the induction of NF-AT forms part of the B cell response to both cross-linking antigens and T cell-generated signals.