Cloning of two members of the SIRPα family of protein tyrosine phosphatase binding proteins in cattle that are expressed on monocytes and a subpopulation of dendritic cells and which mediate binding to CD4 T cells

Abstract

Recent experimental studies have greatly clarified the function of cell surface molecules in the induction and modulation of T cell responses by antigen-presenting cells (APC). However, the differences in ability to stimulate T cells evident for different types and subpopulations of the same APC, such as dendritic cell subsets, is less well understood. This report details an investigation of an antigen expressed on monocytes that is also expressed on a subset of cattle afferent lymph veiled cells (ALVC). A cDNA library derived from cattle monocytes was screened with monoclonal antibodies (mAb) for expression in COS-7 cells. Using separate mAb for screening, two cDNA were cloned, the sequences of which showed a single long open reading frame encoding a predicted type I glycoprotein of 506 amino acids that contained three immunoglobulin superfamily domains and a long 112-amino acid cytoplasmic tail. We have termed this antigen MyD-1, reflecting its myeloid and dendritic cell distribution. Analysis of the EMBL database revealed that the molecule is a member of the recently described family of signal regulatory proteins (SIRP). The outeremost Ig domain was of the adhesion/receptor I-type, suggesting that MyD-1 might bind to a ligand on another cell. Evidence for this was subsequently obtained by demonstrating that COS-7 cells transfected with MyD-1 cDNA bound CD4 T cells and this binding was blocked by specific mAb. The potential importance of this interaction was supported by the finding that the proliferation of resting memory CD4 T cells to ovalbumin-pulsed monocytes was significantly reduced in the presence of mAb to MyD-1. A role for the molecule in the modulation of the monocyte/dendritic APC response is also predicted from the existence of multiple potential tyrosine phosphorylation sites in the cytoplasmic domain, including the presence of an immunoreceptor tyrosine-based inhibitory motif (ITIM) and the observation that the SIRP alpha family members have been shown to bind to SHP-1 and SHP-2. Together these data indicate a possible functional importance for MyD-1 in the regulation of monocyte and dendritic cell function.

High Expression of Inhibitory Receptor SHPS-1 and Its Association with Protein-tyrosine Phosphatase SHP-1 in Macrophages

“…Support for this notion was provided by an earlier report in which purified p94, a brain antigen later found to be SHPS-1 (19), promoted neurite outgrowth when added to neuronal cell cultures (23). Moreover, it was recently observed that SHPS-1 on bovine monocytes interacted with a yet undetermined ligand on CD4 ϩ T-cells, thus improving antigen presentation (20).…”

“…Whereas other studies are needed to elucidate the distribution of SHPS-1 in hemopoietic cells other than macrophages, recent data on the expression of SHPS-1 in bovine tissues provide further clarification (20). Brooke et al (20) found that a bovine hemopoietic cell antigen previously termed MyD-1 was actually SHPS-1.…”

CD47 is a ligand for rat macrophage membrane signal regulatory protein SIRP (OX41) and human SIRPα 1

“…The human CD47 mAb B6H12 used in the former study recognizes the same epitope as BRIC126 [28] which inhibited the binding of purified SIRP to purified CD47. Soluble CD47 mAb inhibited T cell proliferation in a MLR [29] and in complementary experiments, a SIRP mAb blocked antigen-specific T cell proliferation by monocytes [5]. Correlation between SIRP expression and the capacity of APC to stimulate an MLR provides corroborative evidence for SIRP/CD47 engagement promoting T cell activation [30].…”

Signal regulation by family conspiracy

“…The SIRP h subtype has an apparent molecular weight of between 85 and 90 kDa in humans and rats and 110-120 kDa in the mouse. Several groups have discovered a SIRP h-like molecule which has been designated SHPS-1, p84, BIT, MFR, MyD-1 and SIRP h 1 [1,[13][14][15][16][17][18]. For simplicity, all these molecules will be referred to here as SIRP h. SIRP hs are extensively glycosylated and have either three or one immunoglobulin (Ig)-like domains.…”

“…These two transcripts probably reflect the two known variants generated by alternative splicing. SIRP h protein is highly expressed in myeloid cells [17,22,42]. Macrophages may constitute a useful experimental system because they express a single SIRP h far more predominantly than other members [16,31,42,57,58].…”