T cell phenotypes

What is the role of MHC in T cell activation

MHC molecules bind peptide fragments from pathogens and present them to T cells.

• MHC Class I: Presents peptides to CD8+ cytotoxic T cells.

• MHC Class II: Presents peptides to CD4+ helper T cells.

What are the main subsets of CD4+ T cells, and what do they do?

• Th1: Help macrophages, produce IFN-γ, IL-2, and TNF-α.

• Th2: Help B cells, produce IL-4 and IL-5.

• Th17: Pro-inflammatory, induced by TGF-β and IL-6.

• Treg (Regulatory T cells): Suppress immune responses, induced by IL-10 and TGF-β.

What are the primary roles of CD4+ T cells? (T helper)

• Provide "help" by secreting cytokines.

• Regulate immune responses by activating B cells, macrophages, and CD8+ T cells.

How does IFN-γ enhance macrophage activity?

• Stimulates phagocytosis.

• Promotes production of reactive oxygen species (ROS) and nitric oxide for microbial killing.

What is the role of Th2 cells

• Stimulating B cell proliferation and class-switching via CD40 interaction.

• Promoting the production of different antibody isotypes

What are Tregs, and how do they regulate immune responses?

Maintain tolerance and prevent autoimmunity.

• Mechanisms:

  1. Secrete IL-10 and TGF-β to suppress effector T cells.

  2. Interact with APCs to reduce co-stimulatory signals.

What cytokine promotes the differentiation of naïve T cells into Tregs

TGF-β

How are CD8+ T cells activated?

CD8+ T cells are activated by recognizing antigen presented on MHC Class I

What is the role of CD8+ cytotoxic T cells?

• They kill cells infected with intracellular pathogens via:

  • Perforin/Granzyme pathway: Induces apoptosis in target cells.

  • Fas/FasL pathway: Triggers apoptosis via Fas-FasL interaction.

What cytokines determine T cell differentiation?

• IL-12: Promotes Th1 differentiation.

• IL-10: Promotes Treg differentiation.

• TGF-β: Promotes Treg and Th17 differentiation.

• IL-6: Promotes Th17 differentiation

Which T cell subset suppresses immune responses to prevent autoimmunity?

Tregs (Regulatory T cells), through secretion of IL-10 and TGF-β.

How does Fas-FasL interaction induce apoptosis in CD8+ T cell targets?

FasL on CD8+ T cells binds to Fas receptors on the target cell, activating the apoptotic pathway

How does the perforin/granzyme pathway work?

perforin creates pores in the target cell membrane.

Granzymes enter the target cell and induce apoptosis.