Functional analysis of the CD300e receptor in human monocytes and myeloid dendritic cells

The CD300e surface molecule, originally termed immune receptor expressed by myeloid cells (IREM)-2, was reported to associate with the DNAX-activating protein (DAP) 12 adaptor in co-transfected cells, and is capable of signaling. In the present report, we investigated in detail the function of CD300e in monocytes and myeloid DC (mDC) freshly isolated from peripheral blood of normal blood donors. Upon engagement by an agonistic mAb, CD300e triggered an intracellular calcium mobilization and superoxide anion O(2) (-) production in monocytes. Activation via CD300e provided survival signals that prevented monocyte and mDC apoptosis, triggered the production of pro-inflammatory cytokines and upregulated the expression of cell surface co-stimulatory molecules in both cell types. Moreover, CD300e activation of mDC enhanced the alloreactive response of naive T cells. Overall, our data formally support the notion that CD300e functions as an activating receptor capable of regulating the innate immune response in myeloid cells.

A novel recombinantly produced banana lectin isoform is a valuable tool for glycoproteomics and a potent modulator of the proliferation response in CD3+, CD4+, and CD8+ populations of human PBMCs

Lectins as carbohydrate-binding proteins have been employed in various biological assays for the detection and characterization of glycan structures on glycoproteins, including clinical biomarkers in disease states. A mannose-specific banana lectin (BanLec) is unique in its specificity for internal alpha1,3 linkages as well as beta1,3 linkages at the reducing termini. The immunomodulatory potential of natural BanLec was recognized by a strong immunoglobulin G4 antibody response and T cell mitogen activity in humans. To explore its applicability in glycoproteomics and its modulatory potential, the gene of banana lectin was cloned, sequenced and a recombinant protein was produced in Escherichia coli. The obtained cDNA revealed a novel banana lectin isoform, with an open reading frame of 426 nucleotides, encoding a cytoplasmatic protein of 141 amino acids. The molecular mass of rBanLec determined by ESI FT-MS and N-terminal sequencing confirmed the cDNA at the protein level. The specificity of rBanLec for detection glycan structures was the same as for natural BanLec as examined with five protein extracts rich in glycoprotein content, as well as with horseradish peroxidase glycoprotein. Besides, the immunomodulatory potential of rBanLec and nBanLec were comparable as assessed by an inhibition assay and a human T cell proliferation assay where they induced a strong proliferation response in CD3+, CD4+, and CD8+ populations of human PBMCs. This recombinant BanLec is a useful reagent for glycoproteomics and lectin microarrays, with a potential for modulation of the immune response.

Expansion of CD94/NKG2C+ NK cells in response to human cytomegalovirus-infected fibroblasts

CD94/NKG2C(+) natural killer (NK) cells are increased in healthy individuals infected with human cytomegalovirus (HCMV), suggesting that HCMV infection may shape the NK cell receptor repertoire. To address this question, we analyzed the distribution of NK cell subsets in peripheral blood lymphocytes (PBLs) cocultured with HCMV-infected fibroblasts. A substantial increase of NK cells was detected by day 10 in samples from a group of HCMV(+) donors, and CD94/NKG2C(+) cells outnumbered the CD94/NKG2A(+) subset. Fibroblast infection was required to induce the preferential expansion of CD94/NKG2C(+) NK cells that was comparable with allogeneic or autologous fibroblasts, and different virus strains. A CD94-specific monoclonal antibody (mAb) abrogated the effect, supporting an involvement of the lectinlike receptor. Purified CD56(+) populations stimulated with HCMV-infected cells did not proliferate, but the expansion of the CD94/NKG2C(+) subset was detected in the presence of interleukin-15 (IL-15). Experiments with HCMV deletion mutants indicated that the response of CD94/NKG2C(+) NK cells was independent of the UL16, UL18, and UL40 HCMV genes, but was impaired when cells were infected with a mutant lacking the US2-11 gene region. Taken together the data support that the interaction of CD94/NKG2C with HCMV-infected fibroblasts, concomitant to the inhibition of human leukocyte antigen (HLA) class I expression, promotes an outgrowth of CD94/NKG2C(+) NK cells.

IREM-1 is a novel inhibitory receptor expressed by myeloid cells

Using a three-hybrid strategy, we have identified a novel cell surface molecule which interacts with the Src homology 2 (SH2) domains of SH2 domain-containing protein tyrosine phosphatase 1 (SHP-1), termed "immune receptor expressed on myeloid cells 1" (IREM-1). The full-length cDNA coding for a polypeptide of 290 amino acids presents an extracellular single V-type Ig domain, a transmembrane region and a cytoplasmic tail with five tyrosine residues, two of which are in the context of an immunoreceptor tyrosine-based inhibitory motif. Moreover, cDNA encoding for three other splicing forms of IREM-1, named IREM-1 splice variant (Sv)1, Sv2 and Sv3 were cloned by reverse transcription (RT)-PCR. The gene encoding for IREM-1 contains nine exons, is located on human chromosome 17 (17q25.1) and is homologous to previously identified molecules termed CMRF-35 and IRp60. RT-PCR, northern blot and FACS analysis with specific monoclonal antibodies indicated that IREM-1 is expressed on monocytes, granulocytes, and myeloid leukemia cell lines. Western blot analysis confirmed the recruitment of SHP-1 to IREM-1 and demonstrated that phosphotyrosine residue 205 is the main docking site for this interaction. Finally, cross-linking of IREM-1 results in the inhibition of FcRepsilon-induced activation. Our results indicate that IREM-1 is a novel inhibitory receptor of the Ig superfamily in myeloid cells.