IR Quiz

Which of the following is the primary ligand for PD-1?

• CD80

• PD-L1

• Galectin-9

• MHC Class II

Answer explanation

The primary ligand for PD-1 is PD-L1, which binds to PD-1 on T cells, inhibiting their activation and promoting immune tolerance. CD80, Galectin-9, and MHC Class II do not serve as the main ligands for PD-1.

What is the primary role of CTLA-4 in immune regulation?

• Suppressing T-cell activation during chronic infection.

• Enhancing early T-cell activation through co-stimulatory signals.

• Regulating early T-cell activation by competing with CD28 for binding to CD80/CD86.

• Promoting NK-cell cytotoxic activity.

Answer explanation

CTLA-4 primarily regulates early T-cell activation by competing with CD28 for binding to CD80/CD86, thus inhibiting T-cell responses and maintaining immune homeostasis.

Tim-3 interacts with which of the following ligands to induce T-cell exhaustion?

• PD-L1

• Galectin-9

• CD155

• MHC Class II

Answer explanation

Tim-3 primarily interacts with Galectin-9 to induce T-cell exhaustion. This interaction plays a crucial role in the regulation of immune responses, distinguishing it from other ligands like PD-L1, CD155, and MHC Class II.

Which receptor specifically binds to MHC Class II molecules and negatively regulates T-cell activity?

• TIGIT

• LAG-3

• PD-1

• Tim-3

Answer explanation

LAG-3 specifically binds to MHC Class II molecules and plays a crucial role in negatively regulating T-cell activity, making it the correct choice among the options provided.

What is the main effect of TIGIT signaling on immune cells?

• Promoting T-cell activation.

• Suppressing NK-cell and T-cell activation.

• Enhancing macrophage activity.

• Inducing immune checkpoint expression on tumors.

Answer explanation

TIGIT signaling primarily functions to suppress NK-cell and T-cell activation, leading to reduced immune responses. This is crucial for maintaining immune tolerance and preventing excessive inflammation.

Which receptor is primarily expressed on myeloid cells and contributes to immune suppression in the tumor microenvironment?

• CTLA-4

• PD-1

• LILRB4

• LAG-3

Answer explanation

LILRB4 is primarily expressed on myeloid cells and plays a significant role in immune suppression within the tumor microenvironment, making it the correct choice. Other options like CTLA-4, PD-1, and LAG-3 are not primarily myeloid.

What is the downstream signaling motif found in PD-1 that leads to T-cell inhibition?

• ITIM/ITSM

• SHP-1/SHP-2

• CD155/CD112

• CEACAM1

Answer explanation

The PD-1 receptor contains ITIM (Immunoreceptor Tyrosine-based Inhibition Motif) and ITSM (Immunoreceptor Tyrosine-based Switch Motif), which are crucial for recruiting phosphatases that inhibit T-cell activation.

CTLA-4 functions by:

• Binding Galectin-9 to induce apoptosis in effector T cells.

• Blocking CD28-mediated co-stimulatory signaling.

• Suppressing NK-cell activity via CD112.

• Inducing tumor necrosis factor secretion.

Answer explanation

CTLA-4 primarily functions by blocking CD28-mediated co-stimulatory signaling, which is crucial for T cell activation. This inhibition helps regulate immune responses and prevent overactivation of T cells.

Which of the following inhibitory receptors are often co-expressed with PD-1 on exhausted T cells?

• LILRB4

• LAG-3

• TIGIT

• LAG3 and TIGIT

Answer explanation

LAG-3 and TIGIT are commonly co-expressed with PD-1 on exhausted T cells, contributing to their inhibitory functions. This makes 'LAG3 and TIGIT' the correct choice, as they are key markers of T cell exhaustion.

What role does LILRB4 play in the tumor microenvironment?

• Promotes T-cell exhaustion.

• Suppresses myeloid cell activity and inhibits pro-inflammatory signaling.

• Enhances NK-cell cytotoxicity.

• Directly lyses tumor cells.

Answer explanation

LILRB4 suppresses myeloid cell activity and inhibits pro-inflammatory signaling, which helps create an immunosuppressive tumor microenvironment, allowing tumors to evade immune detection.