Recombinant Human Cell surface glycoprotein CD200 receptor 2 (CD200R1L), partial

What is CD200R1L and how does it relate to CD200R1?

CD200R1L (also known as CD200 receptor 2, CD200R2, or CD200RLa) is part of the CD200 receptor family. While CD200R1 is well-characterized as an inhibitory receptor for CD200, CD200R1L may function as an alternative receptor for the CD200/OX2 cell surface glycoprotein . Both belong to the immunoglobulin superfamily, but they have distinct structural and functional characteristics. CD200R1 contains three cytoplasmic tyrosine residues (Y291, Y294, and Y302) that are critical for its signaling functions, with Y302 located within a phosphotyrosine binding domain recognition motif . Unlike most inhibitory receptors, CD200R1 does not contain an immunoreceptor tyrosine-based inhibitory motif (ITIM) .

What cell types express CD200R1L and CD200R1?

CD200R1 expression is primarily restricted to myeloid lineage cells, including:

• Granulocytes

• Monocytes

• Most T-cells

• Neutrophils

• Basophils

• Subsets of NK, NKT, and B-cells

CD200R1L expression patterns are less well-characterized than CD200R1, but research suggests some overlap in expression profiles within immune cell populations. The differential expression patterns between these receptors may contribute to their distinct roles in immune regulation .

How does CD200:CD200R1 signaling function?

When CD200 binds to CD200R1, it triggers phosphorylation of cytoplasmic tyrosine residues (particularly Y302/Y297) by Src kinases . This phosphorylation recruits the adapter protein Dok2 through its phosphotyrosine binding (PTB) domain . The downstream signaling cascade leads to the inhibition of proinflammatory molecule expression, including TNF-alpha, interferons, and inducible nitric oxide synthase (iNOS) . This pathway represents an important myeloid down-regulatory mechanism that may control myeloid function in a tissue-specific manner .

How does CD200R1 signaling impact neutrophil function in inflammatory skin conditions?

CD200R1 signaling plays a critical role in regulating neutrophil recruitment and function during skin inflammation. Research has shown that CD200R1 suppresses neutrophil accumulation in psoriasis-like skin inflammation models . Interestingly, CD200R1 blockade enhances neutrophil recruitment but inhibits reactive oxygen species (ROS) production . This suggests a nuanced role where CD200R1 may control both neutrophil trafficking and activation states.

In mouse models of psoriasis, blocking CD200R1 with antibodies (e.g., OX131) reduces DOK1 phosphorylation and enhances skin inflammation severity, with increased skin thickening, epidermal thickness, and neutrophil accumulation in the skin . This effect was observed in both imiquimod-induced and IL-23 injection models of psoriasis, indicating that CD200R1's role in neutrophil regulation is not model-specific .

What is the differential impact of CD200R1 signaling on macrophages versus neutrophils?

A particularly intriguing aspect of CD200R1 function is its cell type-specific effects. While CD200R1 has been traditionally associated with macrophage regulation, recent research reveals distinct impacts on different myeloid cell types:

This differential impact suggests that CD200R1 signaling has context-dependent and cell type-specific effects, which has important implications for therapeutic targeting of this pathway .

How is the CD200:CD200R1 pathway dysregulated in psoriasis and other inflammatory conditions?

In psoriasis, both CD200 expression and CD200R1 signaling are reduced in non-lesional skin . This dysregulation appears to contribute to the loss of immune control that characterizes psoriasis. The reduced CD200 in non-lesional psoriatic skin may be an underlying factor contributing to disease susceptibility .

The CD200:CD200R1 axis represents a critical regulatory mechanism in skin immunity, with roles in:

• Protecting hair follicles from autoimmune attack

• Mediating UV-induced tolerance to contact allergens

• Regulating responses to infectious agents and self-antigens

The observation that this pathway is compromised in psoriasis provides insight into potential therapeutic approaches that might restore proper immune regulation through CD200:CD200R1 signaling enhancement .

What are the structural and functional differences between CD200R1 and CD200R1L?

While both CD200R1 and CD200R1L (CD200R2) can potentially interact with CD200, they differ in several aspects:

• Signaling mechanisms: CD200R1 contains three critical cytoplasmic tyrosine residues (Y291, Y294, and Y302) that mediate inhibitory signaling through Dok2 recruitment . The signaling mechanisms of CD200R1L are less well-characterized.

• Evolutionary conservation: Humans have only one CD200R1-like gene (CD200R1L), while mice possess multiple CD200R1-like receptors . Until recently, human CD200R1L was not thought to encode a functional protein .

• Glycosylation patterns: CD200R1L exhibits significant glycosylation, appearing as a 45-60 kDa protein despite a predicted core molecular mass of only 25.2 kDa . This extensive glycosylation may influence its binding properties and function.

These differences suggest that CD200R1 and CD200R1L may have evolved distinct roles in immune regulation, potentially providing redundancy or specificity in different contexts .

What are the optimal expression systems for producing recombinant CD200R1L?

When producing recombinant CD200R1L for research purposes, several expression systems have been utilized:

• Human cell expression (HEK-293 cells): This system provides proper post-translational modifications, especially glycosylation, resulting in a protein that more closely resembles the native form. The recombinant protein appears as 45-60 kDa due to glycosylation .

• E. coli expression: While this system offers high yield and cost-effectiveness, it lacks the ability to perform mammalian-type glycosylation. This results in a protein that may have different structural properties than the native form .

For functional studies, especially those examining receptor-ligand interactions, human cell-expressed CD200R1L is preferable as it maintains the glycosylation pattern that may be critical for proper binding to CD200. For structural studies or applications where glycosylation is less critical, E. coli-expressed protein might be sufficient .

What are the most effective methods for studying CD200R1L function in experimental models?

Several experimental approaches have proven valuable for investigating CD200R1L function:

• Blocking antibody studies: Using antibodies like OX131 that block CD200R1 function has revealed important insights into the role of CD200R1 in psoriasis-like skin inflammation . This approach allows for temporal control of receptor inhibition.

• Phosphorylation assays: Measuring DOK1 phosphorylation provides a direct readout of CD200R1 signaling activity. Reduced DOK1 phosphorylation following CD200R1 blockade confirms the inhibition of receptor function .

• In vivo inflammation models: Both imiquimod-induced and IL-23 injection models of psoriasis have been utilized to study CD200R1 function in skin inflammation . These models allow for assessment of inflammatory parameters including skin thickening, immune cell infiltration, and cytokine production.

• Flow cytometry: For analyzing CD200R1L expression on different cell types and monitoring changes during inflammatory responses. This technique has been used to demonstrate that CD200R1 expression on mouse skin immune cells is largely unaffected by psoriasis-like inflammation .

• In vitro functional assays: Stimulating bone marrow-derived macrophages with imiquimod in the presence of CD200R1 blockade allows for assessment of cytokine production and activation marker expression .

How can researchers distinguish between CD200R1 and CD200R1L in experimental systems?

Distinguishing between these related receptors presents technical challenges that can be addressed through several approaches:

When interpreting results, researchers should be aware that humans possess only one CD200R1-like gene (CD200R1L), while mice have multiple CD200R1-like receptors, which complicates cross-species comparisons .