Recombinant Mouse OX-2 membrane glycoprotein (Cd200)

What is the molecular structure and characteristics of mouse CD200?

Mouse CD200 is a 45 kDa type I transmembrane immunoregulatory protein belonging to the immunoglobulin superfamily. The mouse CD200 cDNA encodes a 278 amino acid (aa) precursor with four distinct domains:

• 30 aa signal sequence

• 202 aa extracellular domain (ECD)

• 27 aa transmembrane segment

• 19 aa cytoplasmic domain

The ECD consists of one Ig-like V-type domain and one Ig-like C2-type domain. Within the ECD, mouse CD200 shares 76% and 94% amino acid sequence identity with human and rat CD200, respectively .

What cells express CD200 and CD200R in mice?

CD200 is widely but not ubiquitously expressed across various cell types including:

• B lymphocytes

• A subset of T lymphocytes

• Dendritic cells

• Endothelial cells

• Neuronal cells

In contrast, CD200R expression is primarily restricted to:

• Mast cells

• Basophils

• Macrophages

• Dendritic cells

This expression pattern suggests myeloid cell regulation as the major function of CD200 .

How does mouse CD200 signaling differ from other inhibitory pathways?

CD200R contains tyrosine motifs that can be phosphorylated and signal through the recruitment of the adaptor protein DOK2. This signaling mechanism distinguishes CD200R from almost all other inhibitory receptors, which typically contain immunoreceptor tyrosine-based inhibition (ITIM) motifs that provide inhibition following recruitment of phosphatases . The broad tissue distribution of CD200 and changes in its expression levels provide a mechanism for locally regulating myeloid cell activity at appropriate sites, such as inflamed tissue .

What are the optimal storage and reconstitution conditions for recombinant mouse CD200?

According to product specifications, recombinant mouse CD200 His-tagged protein is:

• Formulated as a lyophilized powder from a 0.2 μm filtered solution in PBS with Trehalose

• Should be reconstituted at 500 μg/mL in PBS

• Shipped at ambient temperature

• Upon receipt, should be stored immediately at the recommended temperature

For carrier-free versions (without BSA), special attention to stability is required as BSA typically enhances protein stability, increases shelf-life, and allows for more dilute storage concentrations .

How can I validate CD200-CD200R interactions in experimental systems?

To effectively validate CD200-CD200R interactions, multiple complementary approaches should be employed:

Biochemical validation:

• Surface plasmon resonance to measure binding kinetics

• Co-immunoprecipitation assays to confirm physical interaction

• ELISA-based binding assays with recombinant proteins

Cellular validation:

• Flow cytometry to detect binding of labeled CD200 to CD200R+ cells

• CD200R+ myeloid cell-CD200+ cell co-culture systems

• Phosphorylation assays to detect downstream signaling events

Functional validation:

• Measure suppression of inflammatory cytokine production

• Assess inhibition of myeloid cell activation markers

• Evaluate functional outcomes in disease models with CD200 or CD200R deletion

How should I design experiments to evaluate CD200's role in tumor immunity?

Based on published methodologies, consider the following experimental design elements:

Model selection:

• Choose appropriate mouse strains (e.g., FVB/N or C57Bl/6)

• For orthotopic studies, consider immunocompromised mice (e.g., Nu/J) with the same MHC haplotype as donor cells

Genetic approaches:

• Use conditional knockout models (e.g., CD200fl/fl)

• Implement cell-specific deletion using Cre-loxP system

• Validate knockdown at both mRNA and protein levels

Analytical methods:

• Perform RNA-Seq profiling of CD11B+CD200R+ cells from CD200+ versus CD200-null tissues

• Conduct flow cytometric analysis of tumor-infiltrating immune cells

• Use in vitro migration/invasion assays to assess functional effects

• Quantify metastasis in vivo following CD200 manipulation

What is known about CD200's role in autoimmunity in mouse models?

CD200 plays a critical role in preventing autoimmune disorders:

• CD200 knockout mice demonstrate increased macrophage numbers and activation

• These mice are predisposed to autoimmune disorders

• CD200-CD200R interaction delivers immunosuppressive signals that regulate immune homeostasis

• The interaction of CD200 with CD200R is important for preventing excessive inflammatory responses in multiple tissues

How does CD200 expression influence chronic lymphocytic leukemia (CLL) diagnosis and prognosis?

CD200 has significant implications in CLL diagnosis and management:

Diagnostic value:

Prognostic significance:

• Data on prognostic value remains limited and somewhat conflicting

• Soluble CD200 levels may correlate with disease progression

• CD200 can be released from CD200+ neoplastic cells by ectodomain shedding regulated by ADAM28

Therapeutic targeting:

• Anti-CD200 antibody (samalizumab) has shown preliminary activity in clinical trials

• Treatment resulted in dose-dependent decrease in CD200 expression on CLL cells

• In phase 1 trials, 14/23 CLL patients showed decreased tumor burden

What mechanisms underlie CD200's promotion of tumor progression and metastasis?

Recent research has identified specific mechanisms by which CD200 promotes tumor progression:

CD200-CD200R axis in cutaneous squamous cell carcinoma (cSCC):

• CD200 stimulates cSCC invasion and metastasis via induction of cathepsin K (Ctsk) in CD200R+ infiltrating myeloid cells

• This pro-metastatic role is independent of direct T cell suppression but modulates the function of infiltrating myeloid cells

• RNA-Seq profiling identified Ctsk as highly upregulated in CD200+ cSCCs compared to CD200-null cSCCs

Cellular mediators:

• CD11B+CD200R+ cells express phenotypic markers associated with myeloid-derived suppressor cell-like cells and tumor-associated macrophages

• These cells are the primary source of Ctsk expression in cSCC

• Induction of Ctsk is dependent on engagement of the CD200-CD200R axis

Functional validation:

• Inhibition of Ctsk, but not matrix metalloproteinases (MMP), significantly blocked cSCC cell migration in vitro

• Targeted CD200 disruption in tumor cells and Ctsk pharmacological inhibition significantly reduced cSCC metastasis in vivo

What is the molecular basis of CD200-CD200R binding specificity?

The molecular basis of CD200-CD200R binding involves specific structural features:

• CD200 and CD200R associate via their respective N-terminal Ig-like domains

• The extracellular domain of mouse CD200 contains one Ig-like V-type and one Ig-like C2-type domain

• High conservation of binding regions across species (mouse CD200 shares 76% and 94% amino acid sequence identity with human and rat CD200, respectively)

• Several viruses encode CD200 homologs that can engage CD200R, suggesting the binding interface can be mimicked by viral proteins

How does CD200R signaling differ from other inhibitory receptor pathways?

CD200R employs a unique signaling mechanism:

• Unlike most inhibitory receptors that utilize immunoreceptor tyrosine-based inhibition (ITIM) motifs and recruit phosphatases

• CD200R contains tyrosine motifs that signal through recruitment of the adaptor DOK2

• This distinctive signaling pathway results in inhibition of myeloid cell activation through mechanisms independent of ITIM-based signaling

• In T cells, CD200 can function as a co-stimulatory molecule independent of the CD28 pathway

What downstream effects occur following CD200-CD200R engagement in different cell types?

CD200-CD200R engagement produces cell type-specific effects:

In myeloid cells:

• Initiates inhibitory signals following receptor-ligand contact

• Suppresses pro-inflammatory cytokine production

• Downregulates activation markers

• Can induce expression of specific proteases like cathepsin K (Ctsk) in tumor-associated myeloid cells

In T cells:

• Functions as a co-stimulatory molecule independent of the CD28 pathway

• May contribute to regulation of T cell responses

In tumor microenvironments:

• Reduces immune reactivity

• Can increase induction/activation of regulatory T cells

• Promotes tumor cell invasion and metastasis through effects on myeloid cells

How can single-cell transcriptomics advance our understanding of CD200-CD200R biology?

Single-cell transcriptomic approaches offer powerful insights into CD200-CD200R biology:

• Can identify heterogeneity within CD200+ and CD200R+ cell populations

• Enables discovery of novel downstream targets of CD200-CD200R signaling (similar to how Ctsk was identified)

• Allows tracking of dynamic changes in gene expression following CD200-CD200R engagement

• Can reveal co-expression patterns with other immunoregulatory molecules

• Facilitates identification of cell-specific responses to CD200-targeting therapies

• Provides insights into differences between CD200R+ cells in different tissue microenvironments

What experimental approaches can resolve contradictory findings regarding CD200's prognostic value?

To address contradictions in CD200's prognostic significance:

• Develop standardized methodologies for CD200 detection and quantification

• Establish clear cutoff values for defining "high" versus "low" expression

• Perform studies on larger cohorts of patients with appropriate statistical power

• Stratify analyses by genetic background, disease stage, and treatment history

• Simultaneously measure membrane-bound and soluble CD200 forms

• Integrate CD200 expression with other established prognostic markers

• Develop robust mouse models that accurately recapitulate human disease dynamics

How might combinatorial targeting of CD200 with other immune checkpoints enhance anti-tumor responses?

This advanced research direction explores potential synergistic approaches:

• Investigate crosstalk between CD200-CD200R and other immune checkpoint pathways (PD-1/PD-L1, CTLA-4)

• Test combinations of anti-CD200 treatment with established checkpoint inhibitors

• Evaluate whether CD200 blockade can reprogram suppressive myeloid cells toward an anti-tumor phenotype

• Develop biomarkers to identify patients most likely to benefit from CD200-targeted therapy

• Assess whether CD200 expression correlates with resistance to other immunotherapies

• Target both CD200 and downstream effectors (e.g., Ctsk inhibitors combined with anti-CD200)

How can researchers distinguish between effects mediated by membrane-bound versus soluble CD200?

Differentiating between membrane-bound and soluble CD200 effects requires careful experimental design:

Isolation strategies:

• Use cell sorting to separate CD200+ cells from their culture supernatants

• Employ size-exclusion methods to separate soluble CD200 from membrane vesicles

• Create experimental models expressing only membrane-anchored or secreted forms

Detection approaches:

• Measure soluble CD200 using sensitive ELISAs

• Assess membrane CD200 via flow cytometry with surface staining

• Remember that CD200 can be released from CD200+ cells by ectodomain shedding regulated by ADAM28

Functional comparisons:

• Design parallel experiments comparing effects of cell-bound versus soluble recombinant CD200

• Note that both membrane and soluble forms can engage CD200R

• Effects may differ in magnitude or kinetics depending on presentation form

What controls are essential when creating CD200 knockout mouse models?

Based on published conditional knockout approaches:

Model validation:

• Confirm deletion at genomic, mRNA, and protein levels

• Assess potential compensatory upregulation of related molecules

• Verify that targeting strategy doesn't affect adjacent genes

Control selection:

• Include Cre-negative littermates as controls

• Consider heterozygous animals to assess dose-dependent effects

• Backcross onto consistent genetic backgrounds to minimize strain-dependent effects

Phenotypic assessment:

• Examine baseline immune cell populations in relevant tissues

• Evaluate for any developmental abnormalities

• Consider that effects may be context-dependent and reveal themselves only upon immune challenge

What are key considerations when using recombinant CD200 in functional assays?

When designing functional assays with recombinant CD200:

Protein quality:

• Consider carrier-free preparations when BSA might interfere with downstream applications

• Store reconstituted protein in small aliquots to avoid freeze-thaw cycles

• Verify activity through binding assays prior to functional experiments

Experimental design:

• Include appropriate controls (CD200-null, blocking antibodies)

• Test dose-response relationships to determine optimal concentrations

• Consider the timing of CD200 addition relative to activation stimuli

Readout selection:

• Choose assays that measure known CD200-dependent outcomes

• Consider both immediate (signaling) and delayed (functional) responses

• Validate findings using multiple complementary approaches

How might therapeutic targeting of the CD200-CD200R axis be optimized for cancer immunotherapy?

Optimizing CD200-targeted therapies requires addressing several factors:

• Development of high-affinity antibodies or small molecules that block CD200-CD200R interaction

• Characterization of biomarkers to identify patients most likely to respond to CD200-targeted therapy

• Investigation of combination approaches with established immunotherapies

• Understanding mechanisms of resistance to CD200 blockade

• Evaluation of dual targeting strategies (e.g., CD200 blockade plus cathepsin K inhibition)

• Development of CD200-based CAR-T cell approaches

What are the implications of viral CD200 homologs for understanding immune evasion mechanisms?

Viral CD200 homologs provide insights into immune evasion:

• Several viruses encode CD200 homologs expressed during the lytic phase

• Like CD200 itself, viral CD200 homologs suppress myeloid cell activity

• This enables increased viral propagation through immune suppression

• Studying viral homologs may reveal essential structural features of CD200-CD200R interaction

• Could lead to development of novel inhibitors targeting this immune evasion strategy

How does the CD200-CD200R axis contribute to tissue-specific homeostasis beyond immune regulation?

Beyond immune regulation, CD200-CD200R signaling may have broader roles:

• Potential contributions to neuronal development and function (given expression on neuronal cells)

• Possible roles in vascular development or angiogenesis (given endothelial expression)

• Investigation of CD200's role in tissue repair and regeneration processes

• Exploration of CD200's contribution to stem cell niche maintenance

• Assessment of metabolic effects resulting from CD200-CD200R signaling in different tissues