Lesson 3: Receptors and Signaling in B and T Cells PDF

**LESSON 3** **Receptors and Signaling: B and T Cell receptors** **Objectives** At the end of the lesson, students can: 1. describe the basic principles of receptor-ligand interaction 2. explain receptor-ligand interaction interactions initiate signaling in B and T cells, as evidenced by...

**LESSON 3** **Receptors and Signaling: B and T Cell receptors** **Objectives** At the end of the lesson, students can: 1. describe the basic principles of receptor-ligand interaction 2. explain receptor-ligand interaction interactions initiate signaling in B and T cells, as evidenced by successfully completing a diagram labeling activity with 90% accuracy 3. identify and explain at least three common strategies used in cellular signaling pathways, such as phosphorylation, second messengers, and protein-protein interactions 4. outline the key steps in at least two frequently encountered signaling pathways in B and T cells 5. describe the structural components of antibodies, including the variable and constant regions, and their roles in immune response 6. explain the process of signal transduction in B cells from receptor engagement to activation of downstream signaling molecule 7. describe the structure of T-cell receptors and outline the major steps involved in T-cell receptor signaling **Introduction** The immune system is a highly intricate network of cells and molecules designed to protect the body from pathogens and other foreign substances. Central to this defense mechanism are B and T lymphocytes, which play crucial roles in recognizing and responding to specific antigens. The ability of these cells to identify and react to a vast array of antigens is mediated by specialized molecules known as receptors---specifically, B cell receptors (BCRs) and T cell receptors (TCRs). These receptors are essential components of the adaptive immune system, enabling highly specific and long-lasting immune responses. BCRs and TCRs are integral membrane proteins that bind to antigens with high specificity. BCRs are found on the surface of B cells and can recognize free antigens directly, leading to the production of antibodies. TCRs, on the other hand, are present on T cells and recognize antigens only when presented by major histocompatibility complex (MHC) molecules on the surface of other cells. The activation of BCRs and TCRs initiates complex intracellular signaling cascades that result in various immune responses, including cell proliferation, differentiation, and cytokine production. These signaling pathways are finely tuned and tightly regulated, ensuring that the immune response is appropriate and effective. Understanding the molecular mechanisms underlying BCR and TCR signaling is crucial for unraveling the complexities of immune function and has significant implications for the development of immunotherapies and vaccines. a. **RECEPTOR LIGAND INTERACTION** Receptor-ligand interactions are fundamental to cellular communication and signaling processes, governing a wide range of biological activities. These interactions involve the binding of a ligand, which is a molecule such as a hormone, neurotransmitter, or antigen, to a specific receptor on the surface of or within a cell. Here are the basic principles of receptor-ligand interactions: **1. Specificity** Receptor-ligand interactions are highly specific, meaning that a particular ligand will only bind to its corresponding receptor, much like a lock and key. **Mechanism**: This specificity is determined by the unique three-dimensional shape and chemical properties of both the receptor\'s binding site and the ligand. The binding site on the receptor is complementary to the ligand, allowing for precise molecular recognition. **2. Affinity** **Mechanism**: High-affinity interactions involve strong binding between the receptor and ligand, often due to multiple non-covalent forces such as hydrogen bonds, ionic bonds, van der Waals forces, and hydrophobic interactions. The higher the affinity, the more likely the ligand will remain bound to the receptor. **3. Saturation** Saturation occurs when all available receptors are occupied by ligands. **Mechanism**: As ligand concentration increases, more receptors become occupied until all are saturated. Beyond this point, increasing ligand concentration does not increase the response, as all receptors are already engaged. **4. Reversibility** Most receptor-ligand interactions are reversible, allowing the ligand to dissociate from the receptor after a certain period. **Mechanism**: The reversibility is critical for dynamic biological processes, enabling cells to respond to changes in ligand concentrations and allowing for the termination of signaling once the ligand is removed or degraded. **5. Agonists and Antagonists** **Agonists**: Ligands that bind to receptors and activate them to produce a biological response. **Antagonists**: Ligands that bind to receptors but do not activate them. Instead, they block the receptor\'s ability to interact with its natural agonist, preventing a biological response. **6. Signal Transduction** The binding of a ligand to its receptor often triggers a conformational change in the receptor that initiates a signaling cascade within the cell. **Mechanism**: This signal transduction process leads to various cellular responses, such as gene expression, cell proliferation, or changes in cellular metabolism, depending on the type of receptor and cell involved. **7. Equilibrium** The interaction between receptors and ligands is often described by an equilibrium between the bound and unbound states. b. **COMMON STRATEGIES USED IN MANY SIGNALING PATHWAYS** Signaling pathways are vital communication networks within cells that allow them to respond to external stimuli, coordinate activities, and maintain homeostasis. Despite the diversity of cellular signals and responses, many signaling pathways share common strategies to efficiently transmit and regulate signals. Here are some of the most common strategies used in signaling pathways: **1. Signal Amplification** - **Definition**: Signal amplification refers to the process by which a single ligand-receptor interaction triggers the activation of multiple downstream signaling molecules, leading to a large-scale cellular response. - **Mechanism**: This often involves enzyme cascades, where one activated enzyme catalyzes the activation of many molecules of a downstream enzyme. For example, in the cAMP signaling pathway, one activated adenylate cyclase enzyme can produce numerous cAMP molecules, amplifying the signal. **2. Modularity** - **Definition**: Modularity involves using distinct signaling modules or domains that can be reused in different contexts or pathways. - **Mechanism**: Signaling proteins often contain modular domains that can bind to various other proteins or lipids, allowing them to participate in multiple signaling pathways. For example, SH2 domains recognize phosphorylated tyrosines and are involved in many different signaling cascades. **3. Scaffolding and Localization** - **Definition**: Scaffolding proteins and cellular localization mechanisms organize signaling components to ensure precise and efficient signal transduction. - **Mechanism**: Scaffolding proteins bring together multiple signaling proteins into a complex, enhancing the speed and specificity of signaling. Localization strategies include the targeting of signaling molecules to specific cellular compartments or membranes, ensuring that signals are directed to the appropriate cellular machinery. **4. Feedback Regulation** - **Definition**: Feedback regulation involves mechanisms by which a signaling pathway is modulated by its own products or outcomes. - **Mechanism**: Negative feedback loops can decrease the activity of upstream components to prevent overactivation, ensuring that the pathway\'s output is tightly controlled. Conversely, positive feedback loops can enhance the pathway\'s activity, reinforcing the signal and leading to sustained responses. For example, in the MAPK pathway, the activation of downstream kinases can feed back to inhibit upstream signaling. **5. Cross-Talk Between Pathways** - **Definition**: Cross-talk refers to interactions between different signaling pathways, allowing cells to integrate multiple signals and coordinate complex responses. - **Mechanism**: Signaling proteins can participate in multiple pathways, or signals from one pathway can modulate the activity of another. For example, the PI3K/AKT pathway and the MAPK pathway often interact, influencing each other's activity and cellular outcomes. **6. Post-Translational Modifications** - **Definition**: Post-translational modifications (PTMs) refer to chemical modifications of signaling proteins after they are synthesized, altering their function or activity. - **Mechanism**: Common PTMs include phosphorylation, ubiquitination, acetylation, and methylation. Phosphorylation, for example, is a key regulatory mechanism in many signaling pathways, where kinases add phosphate groups to proteins, altering their activity, localization, or interactions with other proteins. **7. GTPase Switches** - **Definition**: GTPase switches involve small GTP-binding proteins (GTPases) that cycle between active (GTP-bound) and inactive (GDP-bound) states. - **Mechanism**: GTPases like Ras play crucial roles in signaling pathways by acting as molecular switches. When bound to GTP, they are active and can interact with downstream effectors. GTPase-activating proteins (GAPs) enhance the hydrolysis of GTP to GDP, turning off the signal, while guanine nucleotide exchange factors (GEFs) promote the exchange of GDP for GTP, reactivating the GTPase. **8. Compartmentalization** - **Definition**: Compartmentalization refers to the spatial organization of signaling components within specific cellular compartments, allowing distinct signaling events to occur in different areas of the cell. - **Mechanism**: By compartmentalizing signaling molecules within particular regions of the cell, such as the plasma membrane, endosomes, or nucleus, cells can ensure that signals are transmitted accurately and only to intended targets. This also allows cells to segregate and independently regulate different signaling events. **9. Redundancy** - **Definition**: Redundancy in signaling pathways refers to the existence of multiple components or pathways that can produce similar cellular outcomes, providing robustness to the signaling network. - **Mechanism**: Redundant pathways ensure that critical cellular functions are maintained even if one pathway is inhibited or fails. For example, multiple growth factor receptors can activate the same downstream signaling cascades, ensuring cell survival and proliferation. **10. Temporal Dynamics** - **Definition**: Temporal dynamics refer to the timing and duration of signaling events, which can influence the outcome of the signaling pathway. - **Mechanism**: The timing of signal initiation, the duration of pathway activation, and the timing of feedback loops all contribute to the overall cellular response. For instance, transient vs. sustained ERK activation can lead to different cellular outcomes, such as cell proliferation or differentiation. The aforementioned strategies allow cells to process complex information and respond appropriately to their environment, maintaining cellular homeostasis and enabling a wide range of biological processes. **C. FREQUENTLY ENCOUNTERED SIGNALING PATHWAYS** In the context of immunology, several key signaling pathways play critical roles in the development, activation, and regulation of immune responses. These pathways help immune cells, such as B cells, T cells, macrophages, and others, respond to pathogens, maintain immune homeostasis, and prevent autoimmunity. Here are some of the most frequently encountered signaling pathways in immunologic functions: **1. T Cell Receptor (TCR) Signaling Pathway** - **Overview**: The TCR signaling pathway is central to T cell activation, differentiation, and function. When a T cell recognizes an antigen presented by the major histocompatibility complex (MHC) on an antigen-presenting cell (APC), it triggers a signaling cascade. - **Key Components**: TCR, CD3 complex, ZAP-70, Lck, LAT, SLP-76, PLC-γ, MAPK/ERK, NFAT, NF-κB, AP-1. - **Function**: TCR signaling leads to T cell activation, cytokine production, proliferation, and differentiation into various T cell subsets, such as helper T cells (Th), cytotoxic T cells (Tc), and regulatory T cells (Tregs). **2. B Cell Receptor (BCR) Signaling Pathway** - **Overview**: BCR signaling is essential for B cell activation, proliferation, antibody production, and class switching. B cells recognize antigens through their BCRs, leading to downstream signaling events. - **Key Components**: BCR, Igα/Igβ complex, Src-family kinases (Lyn, Fyn), Syk, BLNK, PLC-γ2, BTK, PI3K, Akt, NF-κB, MAPK. - **Function**: BCR signaling promotes B cell survival, activation, and differentiation into plasma cells that produce antibodies or memory B cells for long-term immunity. **3. NF-κB Signaling Pathway** - **Overview**: NF-κB is a transcription factor that plays a pivotal role in regulating immune responses, inflammation, and cell survival. It is activated by various receptors, including TCRs, BCRs, and cytokine receptors. - **Key Components**: IκB kinase (IKK) complex, IκB, NF-κB dimers (e.g., p65/RelA, p50), TNF receptor, IL-1 receptor, TLRs. - **Function**: Upon activation, NF-κB translocates to the nucleus, where it induces the expression of genes involved in immune responses, inflammation, and cell survival. It is critical for the immune system\'s ability to respond to infections and maintain homeostasis. **4. JAK-STAT Signaling Pathway** - **Overview**: The Janus kinase (JAK)-Signal Transducer and Activator of Transcription (STAT) pathway is essential for transmitting signals from cytokine receptors to the nucleus, influencing gene expression and immune cell function. - **Key Components**: Cytokine receptors, JAKs (JAK1, JAK2, JAK3, Tyk2), STAT proteins (e.g., STAT1, STAT3, STAT5), SOCS proteins (negative regulators). - **Function**: When cytokines bind to their receptors, JAKs are activated, leading to the phosphorylation and activation of STAT proteins, which then dimerize and translocate to the nucleus to regulate gene expression. This pathway is crucial for immune cell development, differentiation, and function. **5. MAPK/ERK Signaling Pathway** - **Overview**: The mitogen-activated protein kinase (MAPK) pathway, particularly the extracellular signal-regulated kinase (ERK) branch, is involved in cell proliferation, differentiation, and survival in response to external stimuli, including immune signals. - **Key Components**: Ras, Raf, MEK, ERK, Elk-1, Fos, Jun. - **Function**: This pathway is activated downstream of various receptors, including TCRs, BCRs, and growth factor receptors. It regulates gene expression and cellular responses, contributing to the immune system\'s ability to respond to pathogens and other challenges. **6. PI3K-Akt Signaling Pathway** - **Overview**: The phosphoinositide 3-kinase (PI3K)-Akt pathway is involved in promoting cell survival, growth, and metabolism. It is activated by a variety of immune receptors, including TCRs, BCRs, and cytokine receptors. - **Key Components**: PI3K, PIP3, Akt (Protein Kinase B), mTOR, PTEN (negative regulator). - **Function**: Activation of this pathway leads to the promotion of cell survival, growth, and metabolism, which are essential for the function and maintenance of immune cells. It also plays a role in regulating the immune response to ensure it is effective and not excessive. **7. Toll-Like Receptor (TLR) Signaling Pathway** - **Overview**: Toll-like receptors (TLRs) are a critical component of the innate immune system, recognizing pathogen-associated molecular patterns (PAMPs) and initiating immune responses. - **Key Components**: TLRs (e.g., TLR4, TLR9), MyD88, TRIF, IRAK, TRAF6, NF-κB, MAPKs. - **Function**: TLR signaling activates inflammatory responses by inducing the production of cytokines, chemokines, and other immune mediators. It is essential for the early detection of pathogens and the initiation of the immune response. **8. Notch Signaling Pathway** - **Overview**: The Notch signaling pathway is involved in cell fate determination, differentiation, and development, particularly in the immune system. - **Key Components**: Notch receptors (Notch1-4), Delta and Jagged ligands, CSL (CBF1/Su(H)/LAG-1), NICD (Notch intracellular domain). - **Function**: In immune cells, Notch signaling is crucial for the differentiation of T cells, including the development of various T cell subtypes, and influences the fate of other immune cells. It helps regulate the balance between different immune cell lineages. **9. Cytokine Signaling via Receptor Tyrosine Kinases (RTKs)** - **Overview**: Receptor tyrosine kinases (RTKs) are a class of receptors that are activated by cytokines and growth factors, playing a significant role in immune cell development and function. - **Key Components**: RTKs (e.g., IL-2R, GM-CSFR), Src-family kinases, PI3K, MAPKs, STATs. - **Function**: RTK signaling regulates a variety of cellular processes, including proliferation, differentiation, and survival of immune cells. This pathway is particularly important in hematopoiesis and the regulation of immune responses. **10. Integrin Signaling Pathway** - **Overview**: Integrins are transmembrane receptors that mediate cell adhesion and signaling, playing a critical role in immune cell trafficking, migration, and interactions with the extracellular matrix. - **Key Components**: Integrins (e.g., LFA-1), FAK (focal adhesion kinase), Src-family kinases, PI3K, Rho GTPases. - **Function**: Integrin signaling regulates immune cell adhesion, migration, and cytoskeletal dynamics, which are essential for immune surveillance, tissue infiltration, and interactions with other cells during immune responses. The aforementioned signaling pathways form the backbone of the immune system\'s ability to detect and respond to pathogens, maintain immune homeostasis, and adapt to challenges. Understanding these pathways is critical for developing new immunotherapies, vaccines, and treatments for immune-related diseases **D. STRUCTURAL MAKE-UP OF ANTIBODIES** **Figure 1.** An illustration showing the structural make-up of an antibody. The image includes labeled parts of the antibody, such as the heavy chains, light chains, antigen-binding sites, variable regions (Fab), constant region (Fc), disulfide bonds, and the hinge region. part of the antibody (immunoglobulin) and its function: **1. Heavy Chains** - **Function**: The heavy chains are larger protein subunits of the antibody molecule. They determine the class of the antibody (e.g., IgG, IgA, IgM, IgE, IgD) and play a key role in the antibody\'s effector functions, such as complement activation and binding to cell surface receptors. **2. Light Chains** - **Function**: The light chains pair with the heavy chains to form the antigen-binding sites of the antibody. There are two types of light chains, kappa (κ) and lambda (λ), but their primary function is to contribute to antigen binding. **3. Antigen-Binding Sites (Variable Regions or Fab)** - **Function**: These are the parts of the antibody that specifically recognize and bind to antigens. The variable regions of both the heavy and light chains form the antigen-binding site, which is unique to each antibody and determines its specificity for a particular antigen. **4. Constant Region (Fc Region)** - **Function**: The constant region of the antibody is responsible for mediating immune system interactions once an antigen has been bound. It determines the isotype of the antibody and is involved in binding to Fc receptors on immune cells, as well as activating the complement system. **5. Disulfide Bonds** - **Function**: Disulfide bonds are covalent links that hold the heavy and light chains together, as well as connect the two heavy chains. These bonds provide structural stability to the antibody, ensuring that it maintains its Y-shaped structure. **6. Hinge Region** - **Function**: The hinge region is a flexible segment that connects the Fab regions to the Fc region. This flexibility allows the two antigen-binding sites to move relative to each other, enabling the antibody to bind more effectively to antigens that are spaced differently on the pathogen\'s surface. These parts work together to allow the antibody to recognize and neutralize pathogens, either by directly binding to them or by recruiting other components of the immune system to eliminate the threat. **E. SIGNAL TRANSDUCTION IN B CELLS** Signal transduction in B cells is a crucial process that initiates the immune response upon recognizing antigens. B cells, a type of lymphocyte, are essential in the adaptive immune system. They express B cell receptors (BCRs) on their surface, which are membrane-bound forms of antibodies. When these receptors bind to specific antigens, a signaling cascade is triggered, leading to B cell activation, proliferation, and differentiation into plasma cells that produce antibodies. This lecture will cover the step-by-step process of signal transduction in B cells, along with an illustrative guide. **Step-by-Step Process of B Cell Signal Transduction** **1. Antigen Binding to the B Cell Receptor (BCR)** - **Process**: The BCR, consisting of membrane-bound immunoglobulin (Ig) molecules and associated Igα (CD79a) and Igβ (CD79b) chains, binds to a specific antigen. This antigen could be a part of a pathogen, such as a protein on the surface of a virus or bacterium. - **Outcome**: This binding induces a conformational change in the BCR complex, which is essential for initiating downstream signaling. **2. Cross-Linking of BCRs** - **Process**: The antigen often has multiple epitopes or repeated units that can bind to several BCRs on the same B cell. This leads to the cross-linking (aggregation) of BCRs on the cell surface. - **Outcome**: Cross-linking brings the Igα/Igβ complexes close together, allowing the signaling molecules to interact and initiate the signaling cascade. **3. Activation of Src-Family Kinases** - **Process**: The clustering of BCRs results in the activation of Src-family kinases, such as Lyn, Fyn, and Blk. These kinases phosphorylate the immunoreceptor tyrosine-based activation motifs (ITAMs) present on the cytoplasmic tails of Igα and Igβ. - **Outcome**: Phosphorylation of ITAMs creates docking sites for other signaling molecules. **4. Recruitment and Activation of Syk Kinase** - **Process**: Syk, a tyrosine kinase, is recruited to the phosphorylated ITAMs on Igα and Igβ. Syk then undergoes autophosphorylation, further amplifying the signal. - **Outcome**: Activated Syk kinase initiates a series of downstream signaling events, crucial for B cell activation. **5. Formation of the Signalosome** - **Process**: Syk activation leads to the recruitment of various adaptor proteins, such as BLNK (B cell linker protein), which serves as a scaffold for assembling a multiprotein signaling complex known as the signalosome. - **Outcome**: The signalosome brings together enzymes like phospholipase C-γ2 (PLC-γ2), Bruton's tyrosine kinase (BTK), and others, facilitating the propagation of the signal. **6. Activation of Phospholipase C-γ2 (PLC-γ2)** - **Process**: PLC-γ2 is activated by phosphorylation through BTK. Once activated, PLC-γ2 hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into two secondary messengers: inositol trisphosphate (IP3) and diacylglycerol (DAG). - **Outcome**: IP3 and DAG play critical roles in further propagating the signal by mobilizing intracellular calcium and activating protein kinase C (PKC), respectively. **7. Calcium Mobilization and Activation of NFAT** - **Process**: IP3 binds to receptors on the endoplasmic reticulum, causing the release of calcium ions into the cytoplasm. The increase in intracellular calcium activates the phosphatase calcineurin, which dephosphorylates nuclear factor of activated T cells (NFAT). - **Outcome**: Dephosphorylated NFAT translocates to the nucleus, where it participates in the transcription of genes necessary for B cell activation and differentiation. **8. Activation of the Ras/MAPK Pathway** - **Process**: The Ras/MAPK pathway is activated through the interaction of adaptor proteins with small GTPase Ras. Ras activates the MAPK cascade, including ERK (extracellular signal-regulated kinase). - **Outcome**: Activation of ERK leads to the phosphorylation of transcription factors such as Elk-1, which enters the nucleus and promotes gene expression necessary for B cell proliferation and survival. **9. Activation of the NF-κB Pathway** - **Process**: DAG, generated by PLC-γ2 activity, activates PKC. PKC phosphorylates IκB kinase (IKK), leading to the degradation of IκB, an inhibitor of NF-κB. - **Outcome**: NF-κB is released and translocates to the nucleus, where it activates genes involved in B cell survival, proliferation, and cytokine production. **10. B Cell Activation, Proliferation, and Differentiation** - **Process**: The combined signals from calcium mobilization, NFAT, Ras/MAPK, and NF-κB pathways result in the full activation of B cells. - **Outcome**: Activated B cells proliferate and differentiate into plasma cells, which secrete antibodies, and memory B cells, which provide long-term immunity. **F. T CELL SIGNALING AND ACTIVATION** T cells are central players of the adaptive immune response, which help protect the host against different pathogens ranging from bacteria to fungi and viruses. In order to perform their function, T cells need to be activated, a process that could lead to a variety of responses including proliferation, migration, cytokine production and even apoptosis. The "decision" by T cells to become activated or not is crucial: an inappropriate or exaggerated response could lead to autoimmune diseases while a failure to respond could lead to infection and death. To perform such a complex and sensitive task, T cells must respond to environmental cues that stimulate a complex signaling cascade. In the last few years, the signaling mechanisms that govern T cell activation and their subsequent cellular responses have been closely studied. In the present review we will examine the main signaling cascades involved and discuss several molecules that are being used to specifically block some of these pathways. T cell activation that leads to a productive response (i.e. cytotoxicity of target cells or stimulation of antibody production by B cells) needs two signals. The primary signal (or signal one) is provided by the binding of foreign antigens (usually small peptides from the respective pathogen) to the T cell antigen receptor (TCR) in the context of the class II major histocompatibility complex (MHC). The TCR is a complex of six different polypeptides. The clonotypic α and β chains provide the specificity of the ligand binding by a process of genetic rearrangement that provides millions of receptor variants. While the α and β heterodimer binds directly to the peptide/MHC complex, the engagement of the intracellular signaling machinery is through the invariant components of the TCR: the γ, δ and ε chains (collectively known as the CD3 complex) and the ζ chains^1,2^. Signal two or the costimulatory signal is provided by interaction of coreceptors such as CD28 or CD4 with their counterparts in the antigen presenting cell (APC)^1,2^. The main signaling pathways elicited by binding of the TCR and some of the coreceptors are depicted in Figure 2.  Figure 2. Major Signaling Pathways in T Cell Activation. Please note that not all the molecules involved in the signaling cascades are illustrated here for simplification purposes. **Example: T-CELL SIGNALLING** T lymphocytes, specifically CD4+ T cells, are considered the leaders of the adaptive immune response to protein antigens. These naive, undifferentiated T cells live in the lymphoid tissues (e.g., lymph nodes, spleen) and must produce effector T cells that may be "summoned" to the tumor site. T-cell receptors (TCRs) are formed when DNA recombines during T cell development and are expressed on the surface of naive T cells. These TCRs enable naive T cells to identify peptide antigens that are bound to major histocompatibility complex (MHC) molecules on antigen-presenting cells (APCs). This is the first of two required signals for T cell activation. The second signal comes from the recruitment of co-stimulators. A common co-stimulator is the CD28 receptor and B7 molecules. Other TCRs include CTLA-4, ICOS and PD-1 with ligands homologous to the B7 proteins. After initial T cell activation, expression of costimulatory and coinhibitory molecules will positively or negatively control the growth, differentiation and function of T cell response. Immune checkpoints, including CTLA-4 and PD-1, are regulators that maintain homeostasis, prevent autoimmunity and have the potential to aid in tumor immune evasion.  **T cell activiation and regulation of response.** [Sharma A, et al. Clin Immunol. 2018;doi:10.1016/B978-0-7020-6896-6.00077-6.](https://www.sciencedirect.com/science/article/pii/B9780702068966000776)   Immune checkpoint regulation pathways **Immune checkpoint regulation pathways.** [Jain P, et al. Ther Adv Respir Dis. 2018;doi:10.1177/1753465817750075.](https://journals.sagepub.com/doi/10.1177/1753465817750075) **Step-by-Step Diagram Activity : Signal Transduction in B Cells** 1\. Antigen Binding to BCR - Diagram: Draw a B cell with Y-shaped B cell receptors (BCR) on its surface. Show an antigen binding to the BCR. - Label: \"1. Antigen Binding to BCR\" 2\. Cross-Linking of BCRs - Diagram: Depict multiple BCRs binding to the same or nearby antigens, causing them to cluster together. - Label: \"2. Cross-Linking of BCRs\" 3\. Activation of Src-Family Kinases - Diagram: Draw arrows from the cross-linked BCRs to a set of proteins (Src-family kinases: Lyn, Fyn, Blk) near the membrane. Show these kinases becoming activated. - Label: \"3. Activation of Src-Family Kinases\" 4\. Phosphorylation of ITAMs on Igα/Igβ - Diagram: Draw Igα and Igβ molecules (as small ovals) attached to the BCR. Show the activated Src kinases phosphorylating ITAMs (small \"P\" circles) on these molecules. - Label: \"4. Phosphorylation of ITAMs on Igα/Igβ\" 5\. Recruitment and Activation of Syk Kinase - Diagram: Show Syk kinase being attracted to the phosphorylated ITAMs and becoming activated (draw an arrow from the phosphorylated ITAMs to Syk). - Label: \"5. Recruitment and Activation of Syk Kinase\" 6\. Formation of the Signalosome - Diagram: Illustrate a larger complex forming around Syk, involving adaptor proteins like BLNK, BTK, and PLC-γ2 (draw multiple circles around Syk labeled with these proteins). - Label: \"6. Formation of the Signalosome\" 7\. Activation of PLC-γ2 - Diagram: Show PLC-γ2 becoming activated within the signalosome (circle around PLC-γ2 with an arrow leading to PIP2). - Label: \"7. Activation of PLC-γ2\" 8\. Calcium Mobilization - Diagram: Draw the breakdown of PIP2 into IP3 and DAG by PLC-γ2. Show IP3 leading to the release of calcium (Ca2+) from the endoplasmic reticulum. - Label: \"8. Calcium Mobilization\" 9\. Activation of the Ras/MAPK Pathway - Diagram: Depict a side pathway where Ras activates the MAPK cascade, leading to ERK activation (draw arrows from Ras to MAPK to ERK). - Label: \"9. Activation of the Ras/MAPK Pathway\" 10\. Activation of the NF-κB Pathway - Diagram: Show DAG activating PKC, leading to the degradation of IκB and the release of NF-κB, which translocates to the nucleus. - Label: \"10. Activation of the NF-κB Pathway\" 11\. B Cell Activation, Proliferation, and Differentiation - Diagram: Illustrate the B cell becoming activated, dividing (proliferating), and differentiating into a plasma cell (which secretes antibodies) and memory B cells. - Label: \"11. B Cell Activation, Proliferation, and Differentiation\" **Diagram Layout Tips:** - Start at the top or left with the antigen binding to BCRs and work your way down or across the page. - Use arrows to connect each step in the pathway, showing the flow of the signal. - Color-code different pathways (e.g., calcium mobilization, Ras/MAPK, and NF-κB) to help differentiate them. - Label each step clearly with numbers and short descriptions. - **QUESTIONS:**