Describe the specific molecules required to stimulate the naïve T cell.

Which proteins on the T cell bind to which proteins on the APC?

Which proteins play a role in antigen recognition, in which protein plays a role in cell signaling?

Initial Tcell response occurs within a secondary lymphoid tissue

Molecules the stimulate the naïve T cell:

• Requires MHC/peptide recognition and signaling events by cell surface receptors.
• CD28 found on the T-cell

Proteins that bind on APC:

• B7 (CD80 and CD86)

Antigen Recognition:

Cell Signaling:

• Signal #1 is delivered through the TCR after binding to MHC/peptide
  Signal #2 is delivered through CD28 after binding to the co-stimulators molecule called B7. Two forms of B7 (CD80 and CD86)

To get naïave T cell really stimulated CD3 and CD28 are required for normal T cell activation.

Explain the general rule of IL-2 in T cell activation in clonal expansion.

IL-2: interleukin 2(a cytokine)

General Rule:

• Important for resting T & B cells into the cell cycle
• IL-2 is a central player in T cell activation and clonal expansion, regulating various aspects of T cell function including proliferation, differentiation, survival, and memory formation, thereby contributing to the generation of effective immune responses against pathogens and abnormal cells.

Explain why the B7 protein is not expressed (or is expressed only at low levels) on non-activated APCs, and why the expression levels of B7 increase when the APC is stimulated by a microbial encounter.

B7 not expressed:

• T cells are not being stimulated
• In the skin in scavenging mode

B7 Increase:

• Dendritic cell binds and stimulated by antigen and travels into the vessels and now the lymphnods have lots of B7

Describe the types of cell:cell interactions that take place between an APC and a naïve T cell.

Describe the general process of T cell stimulation following TCR binding to MHC/peptide.

How does this interaction ultimately lead to entry of the cell into the cell cycle and expression of new genes?

Types of cell:cell interactions:

• Initial events of signal transduction
• mostly on CD4 but also happens on CD8

General Process:

• Surface events lead to signal transduction

Entry of cell to cell cycle and new gene expression:

• Ends at genes that were necessary to be on before they were a T cell

Name the different types of effector Th cells.

How do these different types of T helper cells perform their unique functions? (expression of different cytokine profiles).

Effector T-helper cells:

• A cell that's activated becomes somewhat specialized and now is a participant in immune response.

Unique Functions:

• 5 different types of T cells
• T_h1: activate macrophage
• T_h17: enhances neutrophil response
• T_H2:activate cellular and antibody response parasites
• T_FH:activate B cells maturation of antibody response
• T_reg: Suppress other effector T cells

Understand the importance of the interaction that takes place between CD40-L (a protein expressed on surface of and effector Th1 cell, and CD40 (a protein expressed on the surface of a macrophage).

Interaction between CD40-L & CD40:

• Effector T_h1 cells influence the activity of many other cells at the site of infection throug secretion of specific cytokines
• Effector Th1 cells Activate macrophages through secretion of IFN-gamma and through direct cell:cell contact (CD40/CD40L)

Explain the different ways that a Tc is activated to become a CTL. Describe all the critical steps in this process.

Tc is activated to become a CTL:

• CTL= effector cell
• For the most part Cytotoxic T cells require the same activation stimulates as the naïve T cells

Explain how a CTL differentiates between a healthy cell (which it does not kill) and a virus-infected cell (which it will kill).

CTL differentiates between healthy and virus-infected cells:

• Healthy cells cannot produce do not produce MAC combination
• CTL receives only killing signals.

Name the critical components of the CTL granules (perforin and granzyme B).

Explain how they function to kill the target cell. Together these two proteins induce the target cell to die by apoptosis.

Critical Components:

• perforin
• granzyme B

Function to kill the target:

• Together these two proteins induce the target cell to die by apoptosis.