SummaryHuman dendritic cells (DC) can now be generated in vitro in large numbers by culturing CD34 + hematopoietic progenitors in presence of GM-CSF+TNFet for 12 d. The present study demonstrates that cord blood CD34 + HPC indeed differentiate along two independent DC pathways. At early time points (day 5-7) during the culture, two subsets of DC precursors identified by the exclusive expression of CDla and CD14 emerge independently. Both precursor subsets mature at day 12-14 into DC with typical morphology and phenotype (CDS0, CD83, CD86, CD58, high HLA class II). CDla + precursors give rise to cells characterized by the expression of Birbeck granules, the Lag antigen and E-cadherin, three markers specifically expressed on Langerhans cells in the epidermis. In contrast, the CD14 + progenitors mature into CDla + DC lacking Birbeck granules, E-cadherin, and Lag antigen but expressing CD2, CD9, CD68, and the coagulation factor XIlla described in dermal dendritic cells. The two mature DC were equally potent in stimulating allogeneic CD45RA + naive T cells. Interestingly, the CD14 + precursors, but not the CDla + precursors, represent bipotent cells that can be induced to differentiate, in response to M-CSF, into macrophage-like cells, lacking accessory function for T ceils.Altogether, these results demonstrate that different pathways of DC development exist: the Langerhans cells and the CD14+-derived DC related to dermal DC or circulating blood DC. The physiological relevance of these two pathways of DC development is discussed with regard to their potential in vivo counterparts.

SummaryFresh leukemic cells from patients with adult T cell leukemia (ATL) and some ATL-derived T cell hnes show adhesion to human umbilical vein endothelial cells (HUVECs) mainly through E-selectin, but a proportion of this binding remains unaffected by the addition of combinations of antibodies against known adhesion molecules. By immunizing mice with one of such cell hnes, we estabhshed monoclonal antibodies (mAbs), termed 131 and 315, that recognize a single cell surface antigen (Ag) and inhibit the remaining pathway of the adhesion. These mAbs did not react with normal resting peripheral blood mononuclear cells (PBMC) or most of the cell lines tested except for two other human T cell leukemia virus type I (HTLV-I)-infected T cell hnes. After stimulation with phytohemagglutinin (PHA), PBMC expressed Ag 131/315 transiently, indicating that these mAbs define a T cell activation Ag. Western blotting and immunoprecipitation revealed that Ag 131/315 has an apparent molecular mass of 50 kD. Expression cloning was done by transient expression in COS-7 cells and immunological selection to isolate a cDNA clone encoding Ag 131/315. Sequence analysis of the cDNA indicated that it is identical to human OX40, a member of the tumor necrosis factor/nerve growth factor receptor family. We then found that gp34, the hgand of OX40, was expressed on HUVECs and other types of vascular endothehal cells. Furthermore, it was shown that the adhesion ofCD4 + cells ofPHA-stimulated PBMC to unstimulated HUVECs was considerably inhibited by either 131 or 315. Finally, OX40 transfectants of Kit 225, a human interleukin 2-dependent T cell line, were bound specifically to gp34 transfectants of MMCE, a mouse epithelial cell hne, and this binding was blocked by either 315 or 5A8, an anti-gp34 mAb. These results indicate that the OX40/gp34 system directly mediates adhesion of activated T cells or OX40+-transformed T cells to vascular endothehal cells.

We have developed an efficient in vitro class switching system using a subclone (CH12F3) of the IgM+ CH12.LX lymphoma cell line. CH12F3 cells switched from surface IgM+ cells to surface IgA+ cells at a high frequency (50%) after 72 h stimulation with IL-4, transforming growth factor (TGF)-beta and CD40L. No other class isotype-producing cells were detected, indicating that the CH12F3 clone is exclusively committed to IgA isotype switching. To understand the molecular basis of the isotype commitment, we studied the methylation profiles of I region promoters and I region transcription of CH12F3 cells. No germline transcripts other than those from the I alpha region were detected and only the I alpha promoter was demethylated in uninduced CH12F3 cells. TGF-beta, CD40L and IL-4 synergistically induced efficient switch recombination in CH12F3 cells, suggesting that the three stimulations up-regulate different steps of switch recombination in isotype-committed B cells such as CH12F3 cells. Stimulation of CH12F3 cells by IL-4 or TGF-beta, but not by CD40L, induced transient but complete methylation of the I alpha region. TGF-beta and CD40L, but not IL-4, increased the amounts of germline alpha transcripts. We found that the extents of methylation and the amounts of germline transcripts do not necessarily correlate with the efficiency of recombination in induced CH12F3 cells. These results led to the proposal that switch recombination can be separated into at least two phases, i.e. commitment and recombination. The roles of IL-4, TGF-beta and CD40L in the two phases are discussed.

PD-1, a member of the Ig superfamily, was previously isolated from an apoptosis-induced T cell hybridoma 2B4.11 by subtractive hybridization. Expresson of the PD-1 mRNA is restricted to thymus in adult mice. Using an anti-PD-1 mAb (J43), we examined expression of the PD-1 protein during differentiation of thymocytes in normal adult, fetal and RAG-2(-/-) mice with or without anti-CD3 mAb stimulation. While PD-1 was expressed only on 3-5% of total normal thymocytes, approximately 34% of the CD4(-)CD8(-) double-negative (DN) fraction are PD-1(+) cells with two distinct expression levels (low and high). PD-1(high) thymocytes belonged to TCR gammadelta lineage cells. In the DN compartment of the TCR alphabeta lineage, PD-1 expression started at the low level from the CD44(+)CD25(+) stage and the majority of thymocytes expressed PD-1 at the CD44(-)CD25(-) stage in which the thymocytes express TCR beta chains. The anti-CD3epsilon antibody administration augmented the PD-1 expression as well as the differentiation of the CD44(-)CD25(+) DN cells into the CD44(-)CD25(-) DN stage, not only in normal mice but also in RAG-2-deficient mice. The fraction of the PD-1(low) cells in the CD4(+)CD8(+) double-positive (DP) compartment was very small (<5%) but increased by stimulation with the anti-CD3 antibody, although the total number of DP cells was drastically reduced. The results show that PD-1 expression is specifically induced at the stages preceding clonal selection.

8-Hydroxy-2'-deoxyguanosine (8-OHdG) is a mutation-prone (G:C to T:A transversion) DNA base-modified product generated by reactive oxygen species or photodynamic action. G:C to T:A transversions are observed in the p53 and ras genes of UVB-induced skin cancers of mice and in squamous and basal cell carcinomas of human skin exposed to sunlight. In the current study, 8-OHdG formation was evaluated in the epidermis of hairless mice after repeated exposure to UVB, and possible mechanisms involved were studied. Exposure of hairless mice to either 3.4 [2 minimal erythema dose (MED)] or 16.8 (10 MED) kJ/m2 of UVB three times a week for 2 wk induced a 2.5- or 6.1-fold increase, respectively, in the levels of 8-OHdG in DNA, compared to the unexposed controls. An immunohistochemical method using a monoclonal antibody specific for 8-OHdG showed stronger and more extensive staining in the nuclei of UV-irradiated epidermal cells than in those of nonirradiated cells. Western blots probed with antibodies against 4-hydroxy-2-nonenal-modified proteins confirmed the involvement of reactive oxygen species in the epidermal damage induced by chronic UVB exposure. 3-Nitro-L-tyrosine was detected in western blots in a concentration-dependent manner, suggesting that peroxynitrite derived from the reaction of nitric oxide and superoxide, both of which were probably released from inflammatory cells, was involved in modifying the DNA bases. Therefore, the formation of 8-OHdG after UVB exposure appears to be regulated by at least three pathways: photodynamic action, lipid peroxidation, and inflammation and may play a role in sunlight-induced skin carcinogenesis.