CD86 Human

What is the basic structure of human CD86 protein?

Human B7-2/CD86 is a 329 amino acid protein containing a putative 23 amino acid signal peptide, a 224 amino acid extracellular domain, a 21 amino acid transmembrane domain, and a 61 amino acid cytoplasmic domain . It belongs to the immunoglobulin superfamily and is a variably glycosylated protein with a molecular weight ranging from 60-100 kDa . The protein contains two Ig-like domains in its extracellular region that are critical for its interaction with binding partners .

How does CD86 differ from CD80 (B7-1) in structure and function?

Human CD86 (B7-2) shares only 26% amino acid identity with CD80 (B7-1), despite both serving as ligands for CD28 and CTLA-4 . While both molecules provide costimulatory signals, CD86 is typically constitutively expressed on antigen-presenting cells and can be rapidly upregulated, whereas CD80 expression is more strictly induced upon activation . Functionally, CD86 appears to be the dominant costimulatory ligand during primary immune responses, while CD80 may play a more significant role in secondary responses or immune regulation through preferential binding to CTLA-4 .

What are the primary binding partners of CD86 and their relative affinities?

CD86 primarily binds to two receptors: CD28 and CTLA-4 (CD152). Notably, CTLA-4 binds to both B7-1 and B7-2 with a 20-100 fold higher affinity than CD28 . This differential binding affinity has significant implications for immune regulation, as CD28 engagement typically provides positive costimulatory signals, while CTLA-4 engagement is associated with downregulation of the immune response . The higher affinity of CTLA-4 allows it to effectively compete with CD28 for B7 ligands during ongoing immune responses.

Which immune cell populations constitutively express CD86?

CD86 is constitutively expressed on several antigen-presenting cell populations, including interdigitating dendritic cells, Langerhans cells, peripheral blood dendritic cells, memory B cells, and germinal center B cells . Additionally, CD86 is expressed at low levels on monocytes under basal conditions and can be upregulated in response to inflammatory stimuli, particularly interferon-gamma . This constitutive expression pattern differs from that of CD80, which typically requires cellular activation for significant expression.

How is CD86 expression regulated on T cells?

CD86 expression on T cells is induced by long-term stimulation via CD3 and IL-2R and is down-regulated as the cells become quiescent . The CD86-expressing T cells represent a specific subset of memory effector T cells that express CD45RO and high levels of activation markers including CD25, CD54, and HLA-Dr . These cells also selectively express CD30, CD40-ligand, and CD70, and most produce IFN-γ before undergoing apoptosis . This regulated expression suggests CD86 plays a role in T cell-to-T cell interactions during ongoing immune responses.

What is the significance of CD86 expression on hematopoietic stem cells?

CD86 expression on hematopoietic stem cells (HSCs) correlates strongly with their lymphopoietic potential . Progressive loss of CD86 on stem and progenitor cells parallels their loss of lymphopoietic potential, with CD86- CD150+ CD48- HSCs from normal adult mice demonstrating particularly poor ability to restore the adaptive immune system . Levels of CD86 are high on all progenitors with lymphopoietic potential, making it an important marker for identifying HSC subsets with specific differentiation capabilities.

How does the functional role of CD86 differ between APCs and T cells?

On antigen-presenting cells (APCs), CD86 primarily serves as a costimulatory ligand that interacts with CD28 on T cells to provide critical second signals for T cell activation . In contrast, when expressed on T cells, CD86 can enhance the proliferation and production of IFN-γ by anti-CD3 mAb-stimulated naive T cells and induce proliferation of resting allogenic T cells . Interestingly, research indicates no autocrine effect of CD86 in CD86+ T cell activation, suggesting its expression on T cells primarily facilitates T cell-to-T cell interactions rather than self-stimulation .

What are the functional consequences of CD86 loss on HSCs with aging?

CD86- HSCs accumulate in aged mice as well as young mice repeatedly injected with lipopolysaccharide (LPS) . These CD86- HSCs demonstrate reduced capability for self-renewal and impaired ability to restore the adaptive immune system when transplanted . Specifically, absolute numbers of B and T cells are significantly reduced in peripheral blood of CD86- HSC recipients compared to recipients of CD86+ HSCs . This age-associated accumulation of CD86- HSCs may contribute to immunosenescence and reduced lymphopoietic potential observed in aged individuals.

How does the CD86-CD28/CTLA-4 axis regulate the balance between immune activation and tolerance?

The CD86-CD28/CTLA-4 axis represents a critical checkpoint in immune regulation. While CD86 interaction with CD28 promotes T cell activation, proliferation, and cytokine production, its interaction with CTLA-4 (which has 20-100 fold higher affinity) leads to inhibitory signaling and downregulation of the immune response . This dual functionality allows for fine-tuning of immune responses, with the balance shifting toward inhibition as CTLA-4 expression increases on activated T cells. Disruption of this balance is implicated in autoimmune disorders and has been targeted therapeutically in cancer immunotherapy approaches.

What are the optimal methods for detecting CD86 expression in different cell populations?

For flow cytometric analysis of CD86 expression, PE-conjugated or Alexa Fluor 594-conjugated anti-CD86 monoclonal antibodies provide sensitive detection in various cell populations . When analyzing complex populations such as peripheral blood mononuclear cells, co-staining with lineage markers (e.g., CD14 for monocytes) is recommended . For tissue sections, immunohistochemistry can be performed using anti-CD86 monoclonal antibodies with appropriate epitope retrieval techniques, as demonstrated in human appendix tissue where specific staining was localized to lymphocytes . Optimal dilutions should be determined by each laboratory for specific applications.

How can CD86 expression be modulated experimentally for functional studies?

CD86 expression can be experimentally upregulated on monocytes and dendritic cells using interferon-gamma treatment . On T cells, CD86 expression can be induced through long-term stimulation via CD3 and IL-2R . For functional blocking studies, neutralizing anti-CD86 monoclonal antibodies effectively prevent CD86-mediated costimulation . Genetic approaches using siRNA or CRISPR-Cas9 technology can also be employed for more stable and specific modulation of CD86 expression. When designing such experiments, consideration should be given to potential compensatory mechanisms involving other costimulatory molecules.

What are the considerations for isolating and studying CD86+ versus CD86- HSC populations?

Isolation of CD86+ versus CD86- HSC populations requires careful multiparameter flow cytometric analysis and sorting. These populations should be defined within the lineage marker- Sca-1+ c-Kit+ (LSK) CD150+ CD48- HSC compartment . Consideration should be given to the fact that CD86- HSCs have a distinctive high density of CD150, whereas CD86+ HSCs are equally distributed in CD150Hi and CD150Lo populations . Functional assessment of these populations typically requires competitive transplantation assays, where 200 purified HSCs of each phenotype along with competitor bone marrow cells are transplanted into lethally irradiated recipients, followed by long-term analysis of multi-lineage reconstitution .

How is CD86 expression altered during chronic inflammation and aging?

During chronic inflammation, such as that induced by repeated LPS exposure, and in aging, there is an accumulation of CD86- HSCs with reduced lymphopoietic potential . This shift in HSC phenotype correlates with functional defects, including poor self-renewal and diminished ability to restore the adaptive immune system . In activated T cells, CD86 expression increases following stimulation but decreases as cells become quiescent . Understanding these alterations in CD86 expression provides insight into immune dysregulation during chronic inflammation and aging.

What is the relationship between CD86 expression patterns and autoimmune diseases?

Aberrant CD86 expression on antigen-presenting cells has been implicated in various autoimmune conditions by promoting excessive T cell activation. The balance between CD86-CD28 stimulatory signals and CD86-CTLA-4 inhibitory interactions is often disrupted in autoimmune pathologies. Research investigating CD86 expression patterns in autoimmune disease tissues and experimental models is ongoing. Therapeutic strategies targeting the CD86-CD28/CTLA-4 axis, such as CTLA-4-Ig (abatacept), have shown efficacy in treating autoimmune conditions like rheumatoid arthritis by disrupting costimulatory signals.

How does targeting CD86 affect anti-tumor immune responses?

Modulating CD86-mediated costimulation can have significant effects on anti-tumor immunity. Enhanced CD86 expression on dendritic cells and other antigen-presenting cells can promote stronger T cell responses against tumor antigens. Conversely, many tumors employ strategies to downregulate CD86 or enhance CTLA-4 expression/function to evade immune surveillance. Checkpoint inhibitor therapies targeting CTLA-4 (e.g., ipilimumab) work in part by shifting the balance of CD86 interactions away from the inhibitory CTLA-4 receptor and toward the stimulatory CD28 receptor, thereby enhancing anti-tumor T cell responses.

How does CD86 contribute to the functional heterogeneity of hematopoietic stem cells?

Recent research has revealed that CD86 expression helps delineate functionally distinct HSC subsets . CD86 represents an important tool for subdividing HSCs in several circumstances, identifying those unlikely to generate a full spectrum of hematopoietic cells . The discovery that CD86- CD150+ CD48- HSCs from normal adult mice are particularly poor at restoring the adaptive immune system has significant implications for understanding HSC heterogeneity and the relationship between phenotype and function . This marker may help resolve longstanding questions about the developmental relationships between myeloid-biased and lymphoid-biased HSC subsets.

What is the significance of CD86 expression on memory effector T cells?

The expression of functional CD86 on memory effector T cells suggests a previously underappreciated role in T cell-to-T cell interactions during immune responses . These CD86+ T cells can provide costimulatory signals to naive T cells, enhancing their proliferation and cytokine production in response to TCR stimulation . This finding challenges the traditional view that costimulation is primarily provided by professional antigen-presenting cells and suggests that memory T cells may directly contribute to the activation and differentiation of naive T cells during secondary immune responses.

How do alternative splicing variants of CD86 affect its function?

Alternative splicing of human CD86 generates additional isoforms with distinct functional properties . These splice variants include forms that lack both Ig-like domains or specific regions within the extracellular domain . The functional significance of these variants remains an active area of investigation, with potential implications for fine-tuning costimulatory signals and immune regulation. Researchers studying CD86 should consider the potential presence of these variants when designing experiments and interpreting results, particularly when using detection methods that may differentially recognize specific epitopes.