Abstract The precise immunologic functions of CD1d-restricted, CD161+ AV24AJ18 (Vα24JαQ) T cells are not well defined, although production of IL-4 has been suggested as important for priming Th2 responses. However, activation of human Vα24JαQ T cell clones by anti-CD3 resulted in the secretion of multiple cytokines notably important for the recruitment and differentiation of myeloid dendritic cells. Specific activation of Vα24JαQ T cells was CD1d restricted. Expression of CD1d was found on monocyte-derived dendritic cells in vitro, and immunohistochemical staining directly revealed CD1d preferentially expressed on dendritic cells in the paracortical T cell zones of lymph nodes. Moreover, myeloid dendritic cells both activated Vα24JαQ T cells and were susceptible to lysis by these same regulatory T cells. Because myeloid dendritic cells are a major source of IL-12 and control Th1 cell differentiation, their elimination by lysis is a mechanism for limiting the generation of Th1 cells and thus regulating Th1/Th2 responses.
We identified a novel population of human T cells, studied directly ex vivo, that co-express surface B7-1 and intracellular IL-4. These peripheral blood B7-1+/CD4+ T cells expressed cell surface molecules associated with differentiation including CD45RO and MHC class II, yet were CD69– and CD25–. In short-term cultures, T cell receptor (TCR) cross-linking induced further IL-4 production with little IFN-γ or TNF-α. In marked contrast, CD4+ T cells negative for B7-1 expressed intracellular IFN-γ and high amounts of TNF-α but little IL-4 upon TCR cross-linking. The CD4+/B7-1+/IL-4-expressing T cells were of polyclonal origin based on their diverse TCR repertoire. To explore the biological significance of this B7-1+/IL-4+ T cell population and to assess its potential regulatory role in autoimmune disease, we examined whether these T cells isolated ex vivo were altered in subjects with multiple sclerosis (MS). While the frequency of B7-1+ T cells was enhanced in patients with MS as compared to normal subjects, there was a significant diminution of B7-1+/IL-4+ T cells in the patients. The decrease in these IL-4-producing T cells in patients with autoimmune disease is consistent with a possible role as immunoregulatory T cells.
Eukaryotic molecular diversity within the picoplanktonic size-fraction has primarily been studied in marine surface waters. Here, the vertical distribution of picoeukaryotic diversity was investigated in the Sargasso Sea from euphotic to abyssal waters, using size-fractionated samples (< 2 microm). 18S rRNA gene clone libraries were used to generate sequences from euphotic zone samples (deep chlorophyll maximum to the surface); the permanent thermocline (500 m); and the pelagic deep-sea (3000 m). Euphotic zone and deep-sea data contrasted strongly, the former displaying greater diversity at the first-rank taxon level, based on 232 nearly full-length sequences. Deep-sea sequences belonged almost exclusively to the Alveolata and Radiolaria, while surface samples also contained known and putative photosynthetic groups, such as unique Chlorarachniophyta and Chrysophyceae sequences. Phylogenetic analyses placed most Alveolata and Stramenopile sequences within previously reported 'environmental' clades, i.e. clades within the Novel Alveolate groups I and II (NAI and NAII), or the novel Marine Stramenopiles (MAST). However, some deep-sea NAII formed distinct, bootstrap supported clades. Stramenopiles were recovered from the euphotic zone only, although many MAST are reportedly heterotrophic, making the observed distribution a point for further investigation. An unexpectedly high proportion of radiolarian sequences were recovered. From these, five environmental radiolarian clades, RAD-I to RAD-V, were identified. RAD-IV and RAD-V were composed of Taxopodida-like sequences, with the former solely containing Sargasso Sea sequences, although from all depth zones sampled. Our findings highlight the vast diversity of these protists, most of which remain uncultured and of unknown ecological function.
