Paired immunoregulatory receptors facilitate the coordination of the immune response at the cellular level. In recent years, our group characterized chicken homologues to mammalian immunoregulatory Ig-like receptor families. The first part of this review focuses on the current progress on chicken immunoregulatory Ig-like receptor families. One of these receptors is gallus gallus TREM-A1, which was described as the only member of the chicken TREM family with activating potential. The second part of this review presents a study initiated to further characterize ggTREM-A1 expression. For this purpose we established real-time RT-PCR and generated a specific mab to analyze the expression profile of ggTREM-A1 on mRNA and protein level, respectively. GgTREM-A1 mRNA was predominantly expressed in macrophages, but was also detected in brain, bone marrow, bursa, thymus, spleen and PBMC. Analyzing ggTREM-A1 surface expression by mab staining validated the expression on macrophages. Additionally, we showed high expression on blood monocytes, heterophils and NK cells and on monocytes isolated from bone marrow. Moreover, we detected ggTREM-A1 protein also on thrombocytes, B and T cell subsets, but antigen expression seemed to be lower and more variable in these cells. Immunohistochemistry of chicken brain tissue, combining ggTREM-A1 mab and various markers specific for various brain cell subsets showed expression of ggTREM-A1 on microglial cells, but also on neurons, astrocytes and oligodendrocytes. In conclusion, ggTREM-A1 is expressed on a variety of cells, relevant for the immune system, possibly combining physiological function of different mammalian TREM.
Keywords: CD200 receptor; CD200R; CD300 like antigen; CD300L; CHIR; Chicken; Comparative immunology; Ct; DAP; DNAX activating protein; Fc receptor; FcR; GFAP; ITAM; ITIM; ITSM; Immunoregulatory receptor; KIR; LILR; LRC; MBP; Monocytes/macrophages; NK cell; NeuN; Non-mammalian vertebrate; RCA; SIRP; TREM; chicken Ig-like receptor; cycle threshold; glial fibrillary acidic protein; immunoreceptor tyrosine-based activating motif; immunoreceptor tyrosine-based inhibitory motif; immunoreceptor tyrosine-based switch motif; killer Ig-like receptor; leukocyte Ig-like receptor; leukocyte receptor complex; myelin basic protein; neuronal nuclei; ricinus communis agglutinin; signal-regulatory protein; triggering receptor expressed on myeloid cells.
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