Week 2 (Part 2): Adaptive Immunity - Cell Mediated Immunity T-Cells Flashcards
What does cell mediated immunity deal with?
Deals with INTRAcellular bacteria, viruses, and any bacteria that are out of the reach of antibodies and have escaped phagocytosis
Where do T-cells arise?
T Cells arise in the bone marrow
Where do T-cells mature?
- Maturation process?
- What receptors bind to antigen MHC?
Migrate to the Thymus to undergo several steps of maturation
- Maturation process is the expression of surface receptors known at T cell receptors (TCR) and CD4 and CD8 co-receptors
- These are the receptors that bind to the antigen MHC complex at the same time as the TCR-Antigen binding
What can T-lymphocytes be divided into?
1) Helper T-cells (CD4+)
2) Cytotoxic T-Cells (CD8+)
What do MHC class I and class II do?
Major histocompatibility complex (MHC) class I and class II proteins play a pivotal role in the adaptive branch of the immune system. - Both classes of proteins share the task of presenting peptides on the cell surface for recognition by T cells
What can T-cell receptors bind to?
T Cell receptors only bind to protein antigens, specifically peptides: and fortunately all microbes present these protein antigens
How are T-cells activated?
In order for a T Cell Receptors to be activated it must be “presented” with a peptide by a Major Histocompatibility Complex (MHC) molecule
- Each T cell expresses a variable region specific for one unique peptide or antigen
- The variable region forms the antigen binding site
- This MHC-peptide-TCR binding is based on structural fit
What co-receptor does cytotoxic T-cells have vs. Helper T-Cells?
1) T Cytotoxic cells have CD8 co-receptors on their cell surface and interact with peptide MHC class I complex
2) T Helper cells have CD4 co-receptors on their cell surfaces that bind with the peptide MHC class II complex
Describe T-cell activation:
- Prior to activation
- Steps
- Results (2)
Prior to activation, mature T cells are know as Naive T cells (just as with the B cells)
1) Recognition and activation
- Activation of a naïve T cell starts by recognition and binding of TCell Receptor to the MHC – Antigen complex of antigen presenting cell
2) Proliferation and differentiation
- Interleukin -2 which is produced by a naïve T cell signals T cells to start to Proliferate
3) Effector Function
- The Next step is differentiation into effector cells, or memory cells
Results in apoptosis or memory T-cells
What are Helper T-cells?
- What happens when activated?
- What is stimulated (3)?
Helper T cell are the alarm bell of the immune system
- Once activated they start releasing cytokines (chemical alarm bells) whether it’s interferon, Interleukins etc
1) Stimulate NK cells and macrophages for phagocytosis
2) Activate cytotoxic T cells proliferate
3) B cells to keep proliferating
Describe the process of cytotoxic T-cells replication process:
- What binds, and is replicated?
- What is released? What does it do?
- What does this trigger?
Cytotoxic T cell whose variable portion that is specific to the MHC I complex will attach when presented, will bind, and begin to replicate into memory cells and effector cells
The cytotoxic T cells, release toxic enzymes that degrade nucleic acids they do this by Latching on to the abnormal cell and releasing molecules causing gaps or holes forcing the cell to kill itself (Which if you’ll remember is the same mechanism as NK cells!)
This triggers apoptosis of the infected cell and stops replication
How do viruses evade cytotoxic t-cells?
- Examples
Some viruses block peptide presentation by MHC class I molecules to evade the Cytotixic T cell response.
Examples
- herpes virus papillomavirus (HPV) cytomegalovirus adenovirus
Quickly summarize t-cell activation:
So again the cascade of t cell activation includes antigen recognition by the antigen presenting cell binding to the MHC complex
This stimulates clonal expansion and differentiation into effector cells and memory cells within both the T helper Cells and Cytotoxic t cells.
Effector cells deal with current invasion, whereas memory cells circulate for years to have an effect on any future infections of the same pathogen.
