An Interaction between CD200 and Monoclonal Antibody Agonists to CD200R2 in Development of Dendritic Cells That Preferentially Induce Populations of CD4+CD25+ T Regulatory Cells

Abstract

In previous studies we reported that while interaction between the relatively ubiquitously expressed molecule CD200 and one of its receptors, CD200R1, resulted in direct suppression of alloreactivity, engagement of alternate receptors led instead to altered differentiation of dendritic cells (DCs) from marrow precursors, which could in turn foster development of Foxp3+ regulatory T cells. We have explored this effect of engagement of alternate receptors by using a monoclonal agonist Ab to CD200R2 and investigating expression of TLRs on DCs induced in vivo and in vitro after CD200 stimulation in mice in which the gene encoding CD200R1 was deleted. CD200 stimulation was achieved by using either a soluble form of CD200 (CD200Fc) or overexpression of CD200 as a doxycycline-inducible transgene. Although broadly similar effects were seen, consistent with the hypothesis that triggering of CD200R2 does produce DCs with a characteristic TLR repertoire, there are subtle differences in suppression of alloreactivity achieved by CD200 delivered in these two manners, which is consistent with a complexity of CD200:CD200R engagement not previously appreciated.

Expression of a CD200 Transgene Is Necessary for Induction but Not Maintenance of Tolerance to Cardiac and Skin Allografts

“…Our data further strengthen support for the hypothesis forwarded by ourselves and others (19,27,62,64) that a key component of the immunoregulation responsible for both induction and maintenance of prolonged graft survival in these.…”

“…We have previously reported that improved acceptance of skin allografts in mice was associated with increased expression of a number of distinct mRNAs, one of which encoded CD200, a molecule expressed on the surface of dendritic cells DCs 3 (4,12); that using a soluble immunoadhesin (CD200Fc), in which the extracellular domain of CD200 was linked to a murine IgG2aFc region, or in mice which overexpression of a transgenic CD200 was under control of a doxycycline (Dox)-inducible promoter, inhibition of T cell allostimulation and type 1 cytokine production (IL-2, IFN-␥) occurred in vitro and in vivo (13,14); and that CD200-mediated immunoregulation reflected signaling following an interaction with receptors, CD200Rs, on the surface of myeloid and or lymphoid cells (15)(16)(17), which could in turn favor development of "tolerogenic" DCs and/or regulatory T cells (Tregs) that were implicated in enhanced graft survival (18,19). A large and growing body of work confirms the importance of Tregs in transplantation tolerance (20,21) and the interrelatedness of this with DC function (22)(23)(24).…”

Induction of tolerogenic vs immunogenic dendritic cells (DCs) in the presence of GM-CSF is regulated by the strength of signaling from monophosphoryl lipid A (MPLA) in association with glutathione and fetal hemoglobin gamma-chain

“…Cells were washed three times after complement treatment and cultured for 8 d in either Flt3L containing medium (2 ng/ml) or medium with GM-CSF (5 ng/ml) both recombinant cytokines were purchased from Sigma-Aldrich, Canada. DCs were harvested from these respective cultures and stained for FACS analysis using a number of FITC-labeled mAbs (Cedarlane Labs, Hornby, Ontario), including CD11b/c, class II MHC, CD80, CD86 and CD40 [18].…”

“…While only one CD200 ligand exists, there are a family of CD200Rs, R1-5, whose mechanism of action is not the same [17]. Nevertheless, a commonality in CD200R engagement involves induction of subpopulations of Tr, including Tr1 (TGF␤/IL-10 producing cells) induced following CD200:CD200R1 interaction, and Foxp3 + Treg, induced by CD200:CD200R (2)(3)(4) interactions [17,18]. Flt3L and (GM-CSF + IL-4) have in turn been reported to control development of different populations of DCs, with in general DCs induced in the presence of Flt3L having greater immunostimulatory potential than those induced in the presence of (GM-CSF + IL-4) [19][20][21].…”

CD200:CD200R-Mediated Regulation of Immunity

“…Unlike CD200R1, alternate CD200Rs lack cytoplasmic domains able to recruit signaling molecules directly and are thought to function by coopting accessory molecules (e.g., DAP12) for their function [34]. A role for alternate CD200Rs has been reported in regulation of differentiation of "tolerogenic" DCs, able to foster development of Foxp3 + Tregs [35]. Voehringer et al have also suggested a role for an alternate CD200R, expressed in basophils and mast cells, in recruitment of DAP12 to the cell surface.…”