The role of aquaporins in dendritic cell macropinocytosis.

Immature dendritic cells (DCs) constitutively take up large volumes of fluid by macropinocytosis and concentrate the macrosolutes in the endocytic compartment. This concentration mechanism that is the basis of their high capacity to present soluble antigens requires that DCs be capable of rapidly exchanging water across their membranes. We report that two members of the aquaporin family, AQP3 and AQP7, are expressed in immature DCs and are downregulated after maturation. Treatment of DCs with p-chloromercuribenzenesulphonate (pCMBS), a mercuric drug that blocks aquaporins, inhibited uptake and concentration of macrosolutes taken up by fluid phase endocytosis and led to dramatic cell swelling. In contrast, pCMBS did not affect receptor-mediated endocytosis via the mannose receptor. These findings indicate that aquaporins represent essential elements of a volume control mechanism that allows DCs to concentrate macrosolutes taken up via macropinocytosis.

Pvu II polymorphism in the primate homologue of the mouse B144 (LST-1). A novel marker gene within the tumor necrosis factor region.

A Pvu II RFLP was mapped within the LST-1 gene, the human homologue of the mouse B144 sequence, establishing LST-1 as a new marker gene within the TNF region. We investigated the distribution of this Pvu II RFLP in 274 unrelated individuals, 132 additional HLA-DR7-positive individuals, 86 homozygous lymphoblastoid cell lines, and in four families. Seventeen of 274 individuals (6.2%) were heterozygous for the Pvu II restriction site (ADB1 = lack and ADB2 = presence of the Pvu II restriction site). In our study population the polymorphism has a much wider distribution than that previously reported in an analysis of selected haplotypes. Besides a strong association of ADB1 with HLA-B14, -DR7, we found a further association with HLA-B35. These results were also validated by family segregation studies and analyses of homozygous cell lines. In addition, five of 17 individuals carrying the ADB1 allele had HLA types other than B14 or B35, emphasizing that the presence of ADB1 is not limited to the HLA-B14, DR7 haplotype. LST-1 and its polymorphism may be used as an additional marker of the TNF region, where genes responsible for autoimmune diseases are suspected to be localized.

Phenotype and function of human dendritic cells derived from M-DC8(+) monocytes.

Dendritic cells (DC) generated from peripheral blood monocytes have been used with promising results as a new approach for the immunotherapy of cancer. However, at least four different subpopulations of peripheral blood monocytes have been recognized and their contribution to the generation of functional DC is not known. Recently, the monoclonal antibody M-DC8 has been shown to react with 0.2 - 1 % of blood leukocytes. We have identified M-DC8(+) cells as monocytes which represent about 40 % of CD14(low)CD16(+) monocytes. Similar to M-DC8(-) monocytes, they develop in the presence of GM-CSF and IL-4 into a very homogenous population of cells with DC phenotype and function. M-DC8(+) DC show on average a twofold higher expression of HLA class I and class II molecules than M-DC8(-) DC. These DC produce IL-12p75 both in response to LPS and to CD40 ligation. M-DC8(+) DC induced a strong Th1 immune response and were two to four old more potent than M-DC8(-) DC for the priming of cord blood T cells. M-DC8(+) monocytes can be used as a source of very potent dendritic cells with the potential to significantly improve the efficacy of DC-based immunotherapies.

Cloning and genomic characterization of LST1: a new gene in the human TNF region.

The leucocyte specific transcript - 1 (LST1) represents the human homolog of the mouse B144 transcript, encoded within the tumor necrosis factor (TNF) region of the human major histocompatibility complex class III interval. The gene is localized about 4 kilobases upstream of the lymphotoxin beta gene. It spans a polymorphic genomic region encompassing the microsatellites TNFd and TNFe in intron 3 and a polymorphic Pvu II restriction site 260 base pairs downstream of the polyadenylation signal. Isolation of a full-length cDNA clone revealed that LST1 codes for IFN-gamma-inducible 800 nt transcripts, which are present in lymphoid tissues, T cells, macrophages, and histiocyte cell lines. The cDNA contains three long open reading frames (ORF) with the most likely ORF encoding a transmembrane protein. Its close linkage to the TNF genes and pattern of expression point toward a possible role for LST1 in the immune response.

Complex expression pattern of the TNF region gene LST1 through differential regulation, initiation, and alternative splicing.

Recently, a novel gene, LST1, was identified in the tumor necrosis factor region of the HLA complex, 4 kb centromeric of the lymphotoxin beta gene. By analyzing several full-length cDNA clones and the genomic DNA, we identified seven exons and four introns, spanning 2.7 kb. Isolation of mouse LST1 cDNA clones established the open reading frame. LST1 transcription is characterized by four alternative transcription initiation sites and extensive alternative splicing. The derived polypeptides vary with regard to the presence of the hydrophobic N-terminus and in short internal sequences. In addition, alternative splicing results in LST1 mRNAs encoding different carboxy-terminal sequences. LST1 is predominantly transcribed in monocytes, and mRNA levels increase upon stimulation with interferon-gamma, with a concomitant change in the mRNA pattern resulting in an enhanced expression of the short LST1 transcripts. These data suggest that LST1 may have a specific role in monocytes and possibly also in T cells. Moreover, we found that the recently published cDNA 1C7 is encoded just centromeric of LST1.