Identification of novel CD23 transcripts on human T and B lymphocytes and eosinophil cell line

Impact of different mesenchymal stromal cell types on T-cell activation, proliferation and migration

Mesenchymal stromal cells (MSCs) isolated from different tissue sources may present distinct immunomodulatory profiles. As lymphocyte responses are a combination of several distinct steps, we evaluated and compared the impact of MSCs from different sources on the activation, proliferation and migration of T-cells. We demonstrated that tissue-derived MSCs have important immunomodulatory effects. AT-MSCs induced potent anti-proliferative and anti-inflammatory (IFN-γ downregulation) effects and differentially modulated several T-cell activation markers (CD23, CD26, CD45, and CD69). Among all the MSC types tested, only AT-MSCs induced significant downregulation of CD26 and CD45 expression. Of importance, AT-MSCs maintained a sustained expression of CD69. AT-MSCs, particularly following exposure to an inflammatory environment, promoted the migration of lymphocytes into their surrounding environment. The AT-MSCs may increase recruitment of T lymphocytes by upregulation of IL-8 and CCL5 secretion. Following their migration, T-cells interact with MSCs, which can impair lymphocyte proliferation and activation depending on their origin. Inflammatory T-cells appeared to be progressively suppressed, which may lead to a population of lymphocytes with a regulatory phenotype. These findings are relevant, as they increase our understanding of the different immunomodulatory effect of MSCs as well as their behavior in an inflammatory environment.

Identification and expression profiling of a human C-type lectin, structurally homologous to mouse dectin-2

A number of C-type lectins on antigen-presenting cells play an important role in regulating innate immunity. Previously, we identified the mouse C-type lectins (dectin-1, and dectin-2) and human DECTIN-1. To identify human DECTIN-2, we employed degenerative polymerase chain reaction-based cDNA cloning using RNA from human Langerhans cell (LC)-like dendritic cells (DCs). This process yielded a cDNA encoding a C-type lectin with 66.5% amino acid sequence homology to mouse dectin-2, the same gene reported by Kanazawa et al. (J Invest Dermatol 2004: 122: 1522-1524) using the disparate approach of analyzing coding sequences in chromosome 12. Similar to their findings, we found gene expression in lung, spleen, and lymph node. Among resting leukocytes, it was expressed at highest levels by CD14+ monocytes, at lower levels by CD19+ B cells, and not at all by CD4+ T cells. Activation of CD19+ B cells with pokeweed mitogen down-regulated gene expression, whereas expression in CD4+ T cells was induced by Con A. Among our novel findings are an alternatively spliced transcript lacking exon 2, expression in bone marrow and tonsil, expression in CD8+ T cells that is abrogated following activation with phytohemagglutinin, restricted expression to CD1a+ LC within epidermis, and preferential expression by plasmacytoid (rather than myeloid) DC. Finally, we found that treatment with interleukin-4 (IL-4), IL-10, or UVB down regulated gene expression in CD14+ monocytes, whereas granulocyte-macrophage colony-stimulating factor, transforming growth factor-beta1, or tumor necrosis factor-alpha treatment up-regulated it. Our findings may form the basis for understanding the function of human DECTIN-2 in innate immunity.

Identification and Characterization of an Alternatively Spliced Isoform of Mouse Langerin/CD207

The mouse homologue of human Langerin (CD207), a novel Langerhans cells (LC)-restricted C-type lectin that likely participates in antigen recognition and uptake, has been recently identified. In this study, we isolated the mouse Langerin cDNA from murine fetal skin-derived dendritic cells (FSDDC) by subtractive cloning and rapid amplification of cDNA ends (RACE). An alternatively spliced variant of mouse Langerin that lacked the extracellular neck domain (DeltaE3Langerin) was detected in RNA derived from FSDDC and epidermal LC by RT-PCR. In vitro-generated FSDDC and epidermal LC expressed both full-length and DeltaE3Langerin mRNA, but tissue expression was not restricted to skin. Mouse Langerin protein isoforms were readily detected in fibroblasts transfected with cDNAs encoding epitope-tagged Langerin and DeltaE3Langerin. Recombinant DeltaE3Langerin protein localized with transferrin-containing compartments in transfected fibroblasts. Full-length mouse Langerin-bound mannan, whereas DeltaE3Langerin and soluble bacterial recombinant Langerin protein lacking the neck domain did not. Fibroblasts transfected with mouse Langerin cDNA contained typical Birbeck granules (BG) and cored tubules, whereas DeltaE3Langerin cDNA did not induce BG or cored tubule formation in transfected fibroblasts. Developmentally regulated expression of Langerin isoforms provides a mechanism by which Langerin involvement in antigen uptake and processing could be regulated.

Redox status and immune function in type I diabetes families

Because abnormalities in redox balance cluster in type I diabetes families and the intracellular thiol redox status seems to modulate immune function, we aimed to investigate the relationship between oxidative stress and immunological features. We measured oxidative markers, serum proinflammatory cytokines, soluble cytokine receptors and subsets of peripheral blood lymphocytes (by varying combinations of CD4, CD8, CD23 or low-affinity IgE receptor, and CD25 or IL-2 receptor) from 38 type I patients, 76 low-risk (i.e. without underlying islet autoimmunity) non-diabetic first-degree relatives of diabetic patients, and 95 healthy subjects. In type I diabetes families, protein and lipid oxidation was confirmed by the presence of reduced sulphhydryl groups, increased advanced oxidation protein products, and increased plasma and erythrocyte malondialdehyde. Relatives had decreased counts of monocytes, of cells co-expressing CD23 and CD25 and of CD25(+) cells in peripheral blood. Patients with TIDM had similar defects and, in addition, showed decreased counts of peripheral CD4(+)CD8(+) lymphocytes and increased serum levels of soluble receptors for interleukin (IL)-6 and IL-2. Abnormal indicators of oxidative stress were related in part to immune abnormalities. In the whole study group, we found a correlation (multiple R 0.5, P < 0.001) of CD23(+)CD25(+) cells with blood counts of monocytes, CD4(+)CD8(+) cells, CD25(+) cells, basal haemolysis and plasma levels of thiols. In type I diabetics, anti-GAD65 antibody levels were associated (multiple R 0.6, P = 0.01) positively with sIL-6R, negatively with duration of diabetes and CD23(+)CD25(+) counts; plasma creatinine correlated positively (multiple R 0.6, P < 0.001) with both sIL-2R and tumour necrosis factor (TNF)-alpha concentration. Our study reports the first evidence that the oxidative stress observed in type I families is related to immunological hallmarks (decreased peripheral numbers of monocytes as well as cells bearing a CD4(+)CD8(+), CD23(+)CD25(+) and CD25(+) phenotype) from which the involvement of some immunoregulatory mechanisms could be suspected. It remains to be elucidated the course of events culminating in the loss of physiological immune homeostasis and disease pathology.

Cloning of a second dendritic cell-associated C-type lectin (dectin-2) and its alternatively spliced isoforms

Using a subtractive cDNA cloning strategy, we isolated previously five novel genes that were expressed abundantly by the murine dendritic cell (DC) line XS52, but not by the J774 macrophage line. One of these genes encoded a unique, DC-associated C-type lectin, termed "dectin-1." Here we report the characterization of a second novel gene that was also expressed in a DC-specific manner. Clone 1B12 encoded a type II membrane-integrated polypeptide of 209 amino acids containing a single carbohydrate recognition domain motif in the COOH terminus. The expression pattern of this molecule, termed "dectin-2," was almost indistinguishable from that for dectin-1; that is, both were expressed abundantly at mRNA and protein levels by the XS52 DC line, but not by non-DC lines, and both were detected in spleen and thymus, as well as in skin resident DC (i.e. Langerhans cells). Interestingly, reverse transcriptase-polymerase chain reaction and immunoblotting revealed multiple bands of dectin-2 transcripts and proteins suggesting molecular heterogeneity. In fact, we isolated additional cDNA clones encoding two distinct, truncated dectin-2 isoforms. Genomic analyses indicated that a full-length dectin-2 (alpha isoform) is encoded by 6 exons, whereas truncated isoforms (beta and gamma) are produced by alternative splicing. We propose that dectin-2 and its isoforms, together with dectin-1, represent a unique subfamily of DC-associated C-type lectins.

Characterization of novel FcepsilonRII/CD23 isoforms lacking the transmembrane (TM) segment in human cell lines

Human FcepsilonRII/CD23 is an approximately 45 kDa type II transmembrane glycoprotein belonging to the C-type animal-lectin family, and has two isoforms (a and b) that only differ in their intracytoplasmic tails. We previously found that in several human and mouse cell lines there were two additional CD23 transcripts (a' and b') lacking the exon 3 that encodes the entire transmembrane segment and a part of cytoplasmic tails. In this study, we analyzed the putative CD23a' and CD23b' products at protein levels and characterized with rabbit polyclonal antibodies against novel amino-acid sequences of the putative CD23a' and CD23b' molecules (anti-CD23a' Ab, anti-CD23b' Ab). Western blots in COS cells transfected with CD23a' or CD23b' cDNA as well as in vitro translation assays showed that the a' and b' CD23 transcripts were translated to about 40 kDa molecules. These 40 kDa molecules were also recognized by a polyclonal antibody against 25 kDa soluble fragment of human CD23. We also found that human cells having mRNAs for CD23a' and CD23b' expressed protein products recognized specifically by anti-CD23a' or anti-CD23b' Ab, respectively. In addition, the CD23a' and CD23b' molecules in transfected COS cells were resistant to Endo H(f) and PNGase F, although these truncated forms as well as the membrane-associated forms had an asparagine residue responsible for the N-linked glycosylation. Taken together, our results show that the a' and b' CD23 transcripts are expressed and translated in human lymphoid cells and that their translated products are retained in the cytoplasm where they might play an unique regulatory role in the expression of the full-length CD23 on the cell surface.

Upregulated surface expression of intracellularly sequestered Igepsilon receptors (FcepsilonRII/CD23) following activation in human peripheral blood eosinophils

We investigated the regulation, secretion, and surface expression of the low-affinity FcepsilonRII receptor (CD23) in eosinophils isolated from human blood using multiple monoclonal antibodies (mAbs) directed at different epitopes of human CD23. Substantial surface expression of CD23 was not demonstrated in the resting state. Mean fluorescence intensity (MFI) measured by flow cytometry was 7. 1 +/- 0.8 for 9P25 mAb (p = NS) and 15.7 +/- 3.8 for BU38 mAb (p <. 04) versus 5.3 +/- 1.0 for IgG1 isotype control Ab. By contrast, MFI using BU38 mAb was 154 +/- 18 for JY-B lymphocytes (p <.0001 versus eosinophils). Despite weak surface expression, eosinophil permeabilization demonstrated substantial intracellular expression of CD23; MFI was 33.6 +/- 5.2 for 9P25 mAb versus 4.4 +/- 0.43 for IgG control (p <.001). Western blot analysis using both positive and negative controls demonstrated immunological identity with CD23 on JY-B lymphocytes. Activation of eosinophils caused rapid translocation of CD23 to the surface membrane (160 +/- 33 MFI; p <. 005), which was maximal within 30 sec. Secretory CD23 was detected within the perfusate also at 30 sec and was fully reinternalized at 10 min. This is the first demonstration of the presence of intracellular CD23 in human eosinophils. Our data indicate that eosinophils rarely express CD23 on their surface but are capable of transient high-level expression and secretion with rapid reuptake of intracellular stores of CD23.

The alternatively spliced CD64 transcript FcgammaRIb2 does not specify a surface-expressed isoform

Three highly homologous genes (A, B and C) and six transcripts have been identified for the class I human IgG receptor (CD64). The hFcgammaRIa1 isoform encodes the prototypic high-affinity receptor for IgG. The alternatively spliced hFcgammaRIb2 transcript was postulated to exist as a second surface-expressed CD64 isoform on myeloid cells. In this report we assessed this proposed role for hFcgammaRIb2 in detail. As CD64 monoclonal antibodies might not recognize hFcgammaRIb2, we tagged the receptor with an hemagglutinin tag and transfected hFcgammaRIb2tag in the presence of FcR gamma-chain into IIA1.6 cells. Both transcript and protein of hFcgammaRIb2tag were clearly present in transfectants. However, in contrast to the (control) hFcgammaRIa1tag, no surface expression of hFcgammaRIb2tag was detectable with a tag-specific monoclonal antibody. Confocal scan laser microscopy revealed hFcgammaRIb2tag to be retained in the endoplasmic reticulum, resulting in absent plasma membrane expression. These results show hFcgammaRIb2 neither to be surface expressed, nor to represent a separate CD64 isoform. This finding, furthermore, implicates that other FcR transcripts defined at the mRNA level may not represent true FcR isoforms either.

Distinct modulation by interferon-gamma (IFN-gamma) of CD23 expression on B and T lymphocytes of atopic subjects

The low-affinity IgE receptor (FcepsilonRII/CD23) plays a role in IgE production. Cytokines participating in IgE synthesis also modulate CD23 expression on lymphocytes, but whether this modulation is different in atopic subjects remains unclear. We studied CD23 expression on B and T lymphocytes in 10 asthmatic patients with Dermatophagoides pteronyssinus hypersensitivity and 10 healthy non-atopic subjects. Studies were performed by flow cytometry, in phytohaemagglutinin (PHA) or IL-4-stimulated mononuclear cell cultures, alone or in the presence of IFN-gamma. Soluble CD23 (sCD23) released in the culture supernatants was measured by enzyme-linked immunoassay. Both PHA and IL-4 induced the expression of CD23 on lymphocytes of atopic and non-atopic subjects. Whereas PHA increased both the percentage and mean fluorescence intensity of CD23+ B and T cells, IL-4 alone did not increase the percentage of CD23+ T cells. The effects of IFN-gamma were different in both groups, since it was able to reduce the percentage of PHA-stimulated CD23+ T cells only in non-atopic individuals. In non-atopic subjects more than atopic, levels of sCD23 were increased in the supernatants of PHA and IL-4 cultures. These results show that the modulation of CD23 expression is different on B and T cells, and that IFN-gamma acts differently in atopic and non-atopic individuals.

Characterisation of two human dendritic cell-lines that express CD1a, take-up, process and present soluble antigens and induce MLR

Dendritic cells (DC) are bone marrow derived cells present in diverse tissues and organs including the skin, mucosae and blood. DC have a capital role in the afferent pathway of the immune response because of its role in up-take, processing and presenting antigens to immune cells. Human DC are usually identified by the expression of surface CD1a and HLA-DR. Despite the significant recent developments for in vitro generation of DC derived from blood by using cytokines like GM-CSF and IL-4, the studies on DC and specially on human Langerhans cells (LC) have been hampered by the laborious isolation procedure and the small yield of cells obtained by the various methods of isolation used so far. Therefore, a priority has been a search for monoclonal dendritic cell-lines with LC characteristics in order to facilitate the research in this area. The present study reports on the generation of two stable, self-replicant, adherent, dendritic, CD1a+, HLA-DR , CD45RO , CD23/FcERII+ cell-lines that up-take and process soluble antigens but also inducing MLR and antigen-dependent T-cell response.