Immunology T Cell Activation Quiz

Dendritic Cells and T Cell Activation

• Dendritic cells are essential for presenting antigens to T cells. They capture antigens from the environment and migrate to lymph nodes where they interact with T cells.

• Signal 1 - Antigen recognition by the T cell receptor (TCR) is essential for T cell activation. This involves the T cell recognizing a specific antigen presented by the dendritic cell.

• Signal 2 - CD40L:CD40 interactions provide the second signal for T cell activation. CD40L on the T cell binds to CD40 on the dendritic cell, leading to the activation and maturation of the dendritic cell. This results in the increased expression of co-stimulatory molecules like B7.

• CTLA-4:B7 interactions suppress T cell activation. CTLA-4, expressed on activated T cells, competes with CD28 for binding to B7. This interaction delivers an inhibitory signal, dampening T cell activation.

• PD-1 plays a regulatory role by inhibiting T cell activation. It binds to its ligands, PD-L1 and PD-L2, which are expressed on various cells, including tumor cells. This interaction leads to the inhibition of T cell signaling and a reduction in T cell function.

T Cell Co-Stimulatory Pathways and Therapies

• CD40L:CD40 pathway is targeted in clinical trials for its potential in cancer immunotherapy. Therapies blocking the CD40 pathway are being investigated for their ability to enhance antitumor immunity.

• Therapeutic costimulatory blockade, such as CTLA-4 or PD-1 blockade, achieves therapeutic effects by regulating T cell activity. This approach involves blocking inhibitory pathways, allowing T cells to mount a robust response against tumors or pathogens.

IL2: Key Cytokine in T Cell Responses

• IL-2, a key cytokine in T cell responses, is primarily produced by activated T cells. It promotes the growth and differentiation of T cells, enhancing their immune functions.

• CD69 is predominantly expressed on activated T cells. It acts as a marker of activation and its expression is upregulated after T cell stimulation.

T Cell Clonal Expansion and Differentiation

• Clonal expansion refers to the rapid proliferation of activated T cells, creating a large number of identical cells specific for the recognized antigen.

• Foxp3 is crucial for the differentiation and function of regulatory T cells (Tregs). Tregs play a critical role in suppressing immune responses, maintaining tolerance, and preventing autoimmune reactions.

• IL-2 influences the activity of other T cells by promoting the differentiation of effector T cells and supporting the survival and function of Tregs.

Changes in Surface Molecule Expression following T Cell Activation

• Downregulation of CCR7 expression is a key change in surface molecule expression following T cell activation which aids in T cell migration to inflammatory sites.

• CD28 is a surface molecule typically associated with the costimulatory signal necessary for T cell activation. It binds to B7 on antigen-presenting cells, providing the required second signal for T cell activation.

IL-2 Secretion and Adhesion Molecules in T Cell Activation

• Activated T cells are the primary source of IL-2 secretion in the early phase of T cell activation. This IL-2 is crucial for their own proliferation and differentiation into effector cells.

• Adhesion molecules, like LFA-1, facilitate the tight interaction between T cells and antigen-presenting cells. These interactions are essential for the delivery of activation signals and effective immune responses.

Memory T Cells: Properties and Differentiation

• Memory T cells exhibit increased expression of anti-apoptotic proteins, which contributes to their prolonged survival and allows them to respond rapidly upon encountering the same antigen.

• Memory T cells display more rapid and robust responses to antigen stimulation compared to naive T cells, enabling a quicker and more effective immune response upon re-exposure to the same pathogen.

• Cytokines like IL-7 are crucial for the maintenance of memory T cells in the absence of antigen. They provide survival signals and maintain the pool of memory T cells, ensuring a rapid response upon subsequent encounters with the pathogen.

Contraction of T Cell Responses and Memory T Cell Generation

• Elimination of the antigen triggers the contraction of the T cell response. This involves the removal of effector T cells, reducing the immune response to manageable levels.

• A key mechanism behind the decline of T cell responses is the death of activated T cells due to the lack of antigenic stimulation and the withdrawal of survival signals. This ensures that immune responses are controlled and do not persist indefinitely.

• Memory T cells are long-lived and exhibit enhanced survival, allowing them to persist even after the antigen is cleared. This provides rapid and effective immune responses upon re-exposure to the same pathogen.

• Effector cells contribute to the generation of memory T cells. This is achieved through various mechanisms, including the expression of specific transcription factors and the retention of survival signals.

• A greater number of memory T cells compared to naive T cells signifies a more robust and efficient immune response upon reencountering the same antigen. This enables a quicker and more effective defense against previously encountered pathogens, contributing to a more resilient immune system.