Chicken immunoregulatory Ig-like receptor families: an overview and expression details on ggTREM-A1

The Immunological Capacity of Thrombocytes

Thrombocytes are numerous in the blood of aves (birds) and ichthyoids (fish). The origin of this cell type is a common hematopoietic stem cell giving rise to a cell that is active in blood coagulation, inflammatory functions, and the immune response in general. It has been well documented that thrombocytes can phagocytize small particles and bacteria. While phagocytosis with an associated oxidative burst has been reported for chicken thrombocytes, some questions remain as to the degradation capacity of phagosomes in ichthyoids. As innate cells, thrombocytes can be stimulated by bacterial, viral, and fungal pathogens to express altered gene expression. Furthermore, there have been observations that led researchers to state that platelets/thrombocytes are capable of serving as "professional antigen presenting cells" expressing CD40, CD80/86, MHC I, and MHC II. This indeed may be the case or, more likely at this time, provide supporting evidence that these cells aid and assist in the role of professional antigen-presenting cells to initiate adaptive immune responses.

Identification of a novel conserved signaling motif in CD200 receptor required for its inhibitory function

The inhibitory signaling of CD200 receptor 1 (CD200R) has been attributed to its NPxY signaling motif. However, NPxY-motifs are present in multiple protein families and are mostly known to mediate protein trafficking between subcellular locations rather than signaling. Therefore, we investigated whether additional motifs specify the inhibitory function of CD200R. We performed phylogenetic analysis of the intracellular domain of CD200R in mammals, birds, bony fish, amphibians and reptiles. Indeed, the tyrosine of the NPxY-motif is fully conserved across species, in line with its central role in CD200R signaling. In contrast, P295 of the NPxY-motif is not conserved. Instead, a conserved stretch of negatively charged amino acids, EEDE279, and two conserved residues P285 and K292 in the flanking region prior to the NPxY-motif are required for CD200R mediated inhibition of p-Erk, p-Akt308, p-Akt473, p-rpS6 and LPS-induced IL-8 secretion. Altogether, we show that instead of the more common NPxY-motif, CD200R signaling can be assigned to a unique signaling motif in mammals defined by: EEDExxPYxxYxxKxNxxY.

Immunohistochemical identification of T and B lymphocytes in formalin-fixed paraffin-embedded chicken tissues using commercial antibodies

Immunohistochemical method to detect avian lymphocytes is an efficient and reliable tool for accurate diagnosis, and immunological analysis of avian diseases. However, there are scarce studies reporting immunohistochemistry (IHC) using commercially available antibodies in formalin-fixed paraffin-embedded (FFPE) chicken tissues. In the present study, we established an immunohistochemical method to identify chicken T and B lymphocytes in FFPE chicken tissues using commercial antibodies against chicken or human antigens. For this IHC method, the five tested anti-T lymphocyte antibodies reacted with chicken T lymphocytes on the FFPE sections. Further, 10 commercial anti-B lymphocyte antibodies were tested; of these, three successfully detected chicken B lymphocytes for IHC. In particular, anti-human CD3 (clone F7.2.38) antibody was most suitable for the detection of chicken T lymphocytes, whereas anti-chicken B cell activating factor receptor (BAFF-R) antibody (clone 2C4) was most suitable for the detection of chicken B lymphocytes under our IHC staining conditions. These two antibodies reacted with numerous lymphocytes of all representative lymphoid tissues without problematic background staining and nonspecific reactions. Our results indicate that T and B lymphocytes in FFPE chicken tissues can be immunohistochemically detected using commercial antibodies.

Neurons and astrocytes of the chicken hypothalamus directly respond to lipopolysaccharide and chicken interleukin-6

In 4-5-month-old chicken, intravenous injections of bacterial lipopolysaccharide (LPS) induced a dose-dependent fever response and a pronounced increase of circulating interleukin-6 (IL-6). To assess a possible role for IL-6 in the brain of birds, a hypothalamic neuro-glial primary culture from 1-day-old chicken was established. Each well of cultured hypothalamic cells contained some 615 neurons, 1350 astrocytes, and 580 microglial cells on average. Incubation of chicken hypothalamic primary cultures with 10 or 100 µg/ml LPS induced a dose-dependent release of bioactive IL-6 into the supernatant. Populations of hypothalamic neurons (4%) and astrocytes (12%) directly responded to superfusion with buffer containing 10 µg/ml LPS with a transient increase of intracellular calcium, a sign of direct cellular activation. Stimulation of hypothalamic cultures with buffer containing 50 ng/ml chicken IL-6 induced calcium signaling in 11% of neurons and 22% of astrocytes investigated. These results demonstrate that IL-6 is produced in the periphery and in the hypothalamus in response to LPS in chicken. The observed cellular responses of hypothalamic cells to chicken IL-6 indicate that this cytokine may readily be involved in the manifestation of fever in the avian hypothalamus.

The identification, characterization, and function of two TREMs genes in Chinese Yangzhou goose (Anas cygnoides)

Triggering receptor expressed on myeloid cells (TREM) is a cell-surface receptor primarily expressed on macrophages. Here, two novel TREM genes, AcTREM1 and AcTREM2, were identified from Anas cygnoides. AcTREM1 cDNA contained a putative signal peptide, two IG domains, and a transmembrane domain. The deduced AcTREM2 sequence also contained a signal peptide, an IG domain, and a transmembrane domain. qRT-PCR, fluorescence in situ hybridization, and immunofluorescence experiments showed that AcTREM1 and AcTREM2 were mainly expressed in the liver and spleen, and both genes and proteins were mainly distributed in cytoplasm. AcTREM1 expression in the liver and spleen was significantly upregulated following lipopolysaccharide (LPS) challenge at an early stage of infection and then decreased at a later stage. Changes in AcTREM2 expression were reciprocal to those of AcTREM1 in the liver and spleen after LPS challenge. Our results indicate that AcTREM1 and AcTREM2 participate in the antibacterial immunity of A. cygnoides.

Chicken TREM-B1, an Inhibitory Ig-Like Receptor Expressed on Chicken Thrombocytes

Triggering receptors expressed on myeloid cells (TREM) form a multigene family of immunoregulatory Ig-like receptors and play important roles in the regulation of innate and adaptive immunity. In chickens, three members of the TREM family have been identified on chromosome 26. One of them is TREM-B1 which possesses two V-set Ig-domains, an uncharged transmembrane region and a long cytoplasmic tail with one ITSM and two ITIMs indicating an inhibitory function. We generated specific monoclonal antibodies by immunizing a Balb/c mouse with a TREM-B1-FLAG transfected BWZ.36 cell line and tested the hybridoma supernatants on TREM-B1-FLAG transfected 2D8 cells. We obtained two different antibodies specific for TREM-B1, mab 7E8 (mouse IgG1) and mab 1E9 (mouse IgG2a) which were used for cell surface staining. Single and double staining of different tissues, including whole blood preparations, revealed expression on thrombocytes. Next we investigated the biochemical properties of TREM-B1 by using the specific mab 1E9 for immunoprecipitation of either lysates of surface biotinylated peripheral blood cells or stably transfected 2D8 cells. Staining with streptavidin coupled horse radish peroxidase revealed a glycosylated monomeric protein of about 50 kDa. Furthermore we used the stably transfected 2D8 cell line for analyzing the cytoplasmic tyrosine based signaling motifs. After pervanadate treatment, we detected phosphorylation of the tyrosine residues and subsequent recruitment of the tyrosine specific protein phosphatase SHP-2, indicating an inhibitory potential for TREM-B1. We also showed the inhibitory effect of TREM-B1 in chicken thrombocytes using a CD107 degranulation assay. Crosslinking of TREM-B1 on activated primary thrombocytes resulted in decreased CD107 surface expression of about 50-70%.

Chicken CD300a homolog is found on B lymphocytes, various leukocytes populations and binds to phospholipids

The chicken CD300 cluster contains three genes that encode inhibitory, activating and soluble forms. In the present study, we have generated a monoclonal antibody against the inhibitory CD300L-B1 molecule. The mab 1D4 was specific for the CD300L-B1 form and showed no crossreactivity with the related CD300L-X1. Virtually all bursal cells expressed CD300L-B1, whereas only a small positive subset was found in thymus that was identified as thymic B cell subpopulation. In peripheral tissues, CD300L-B1 was found to be expressed on lymphocyte subpopulations in blood and spleen. Double immunofluorescence analysis with B- and T-cell specific markers identified these subsets as B lymphocytes. In addition, analysis of PBMC revealed that CD300L-B1 was also present on monocytes, heterophils, blood NK cells and in vitro differentiated macrophages. We utilized a reporter cell line in order to identify potential ligands of CD300L-B1. When several phospholipids were tested, only phosphatidylserine and phosphatidylethanolamine were found to trigger strong reaction of the reporter cells. The two phospholipids elicited a response only in CD300L-B1 reporter cells, but not in CD300L-X1 reporter cells. Moreover the interaction could be blocked with the specific mab. In conclusion, we provide evidence for the expression of chicken CD300L-B1 on immature and mature B cells, monocytes, heterophils, macrophages and NK cells and identify phosphatidylserine and phosphatidylethanolamine as CD300L-B1 ligands.

Chicken SLAMF4 (CD244, 2B4), a receptor expressed on thrombocytes, monocytes, NK cells, and subsets of αβ-, γδ- T cells and B cells binds to SLAMF2

The SLAM family of membrane receptors is involved in the regulation of immune responses by controlling cytokines production, cytotoxicity as well as cell development, differentiation and proliferation, but has only been described in chickens, recently. The aim of this study was to characterize the avian homologue to mammalian SLAMF4 (CD244, 2B4), a cell surface molecule which belongs to the SLAM family of membrane receptors. We generated a SLAMF4 specific monoclonal antibody (mab) designated 8C7 and analyzed the SLAMF4 expression on cells isolated from various lymphoid organs. Subsets of αβ and γδ T cells found in peripheral blood lymphocytes (PBL) and spleen coexpressed SLAMF4. The expression was restricted to CD8α(+) T cells, whereas CD4(+) T cells and all thymocytes showed little or no reactivity upon staining with the 8C7 mab. Blood and splenic γδ T cells could be further differentiated according to their expression levels of SLAMF4 into two and three subsets, respectively. SLAMF4 was absent from bursal and splenic B cells, however, it was expressed by a distinct fraction of circulating B cells that were characterized by high level expression of Bu1, Ig, and CD40. SLAMF4 was also present on NK cells isolated from intestine of adult chickens or embryonic splenocytes identified by their coexpression of the 28-4 NK cell marker. Moreover, SLAMF4 expression was found on thrombocytes and monocytes. The interaction of SLAMF4 with SLAMF2 was proven by a reporter assay and could be blocked with the 8C7 mab. In conclusion, the avian SLAMF4 expression markedly differs from mammals; it binds to SLAMF2 and will be an important tool to discriminate several γδ T cell subsets.