The maturation of naive CD4 T cells into interleukin (IL)-4-producing effectors was shown to require the presence of IL-4 at priming, the cellular origin of which remains unclear. We demonstrate here that naive T cells themselves release IL-4 at very low levels that are nevertheless sufficient to promote their development into Th2-like cells. This conclusion is based on three observations: (1) highly purified human naive CD4 T cells, of neonatal or adult origin, develop into Th2 effectors upon repetitive cycles of stimulation with anti-CD3 monoclonal antibody (mAb) cross-linked to CD32-B7 transfected L fibroblasts followed by IL-2 expansion; (2) IL-4 protein is readily detectable in the concentrated supernatant fluids of priming cultures performed in the presence of anti-IL-4 receptor mAb; and (3) addition of anti-IL-4 or anti-IL-4 receptor mAb at priming markedly inhibits the acquisition of IL-4- and IL-5-producing capacity while enhancing that of interferon-gamma.

It was recently demonstrated that naive human and mouse CD4 T cells release low but sufficient levels of interleukin (IL)-4 at priming to support their development into IL-4 producers. To determine whether this IL-4 is produced by a minor subset of cells, freshly isolated human naive CD4 T cells were directly cloned by limiting dilution in the absence of exogenous IL-4. More than 95% of neonatal and 60% of adult naive T cells seeded in single-cell cultures could be expanded upon stimulation with anti-CD3 mAb immobilized on CD32-B7.1 L cell transfectants in the presence of IL-2. All 171 clones derived from four neonates and two adults produced IL-4 and IL-5 at generally high levels. Like the allergen-specific human Th2 clones described in the literature, these T cell clones produced little or no interferon-gamma upon stimulation via their T cell receptor/CD3 complex, whereas they released high levels of this cytokine when activated with phorbol 12-myristate 13-acetate+ionomycin. Cells cloned and expanded in the presence of anti-IL4 + anti-IL-4R mAb produced much lower levels of IL-4 and IL-5. It is concluded that almost every single naive human CD4 T cell primed and expanded in the absence of exogenous IL-4 releases sufficient autocrine IL-4 to support its clonal expansion into high IL-4/IL-5 producers.

The current report documents the molecular cloning of the mouse mitochondrial NADP-dependent isocitrate dehydronegase (mNADP-IDH) cDNA. The cDNA was 1,863 bp in length and contained one open reading frame encoding a 523-residue polypeptide with a predicted molecular weight of 58 kDa. The cDNA and the deduced amino acid (AA) sequence of the mouse mNADP-IDH had a high degree of homology with those of porcine, bovine, alfalfa, and yeast. The recombinant mNADP-IDH expressed in Escherichia coli had active enzymatic function, as well as an expected molecular weight. The heart had the highest constitutive expression of the steady-state mNADP-IDH mRNA, followed by the kidney, while the expression of the gene in other tissues was low. The enzymatic activity of different tissues was in agreement with their mNADP-IDH mRNA levels. The resting lymphocytes had low constitutive expression of the gene, but the steady-state mRNA could be induced 48 h after mitogen stimulation. At the protein level, the resting lymphocytes had low enzymatic activity of mNADP-IDH, but the activity was augmented fivefold after mitogen stimulation. The cytosolic NADP-IDH, on the contrary, remained low or undetectable before and after the mitogen stimulation. Based on our current findings as well as the known roles of the mNADP-IDH in anabolism and in the isocitrate shuttle, it is conceivable that the mNADP-IDH i s necessary for optimizing proliferation in lymphocytes.