Question

1. In order to activate the cellular-mediated branch of your adaptive immune system, T cells must be presented with a particular antigen via dendritic cells. Describe the process by which dendritic cells and T cells co-localize with each other to facilitate this interaction, making sure to note where, anatomically, this co-localization occurs?

2.  During the infection described in the previous question, a particular dendritic cell is able to phagocytize and subsequently “digest” an individual Streptococcus pyogenes cell. These antigens can then be presented to lymphocytes to activate an adaptive immune response. Answer both of the following questions based on this scenario.

A) Will this peptide be expressed on a Class I MHC molecule or a Class II MHC molecule on the surface of this APC?

B) Outline the specific biochemical pathway which will lead to the expression of this particular peptide on the plasma membrane of this APC.

Answer 1

1. CELL MEDIATED IMMUNE RESPONSE (CMI)

Immune response mediated by T cells is called cell mediated immunity

T_H cells - TH cells

T_C cells - TC cells

CD8⁺ - CD8+

CD4⁺ - CD4+

Pre- TCR : pre T cell receptor

Naive lymphocytes migrated to peripheral and mucosal lyphocytes.

ITAM -Immunoreceptor Tryosine Based Activation Motif.

ZAP 70 - Zeta chain associated protein kinase 70

There are two types of T_H response. T_{H 1} and T_H2 response.

T_{H 1} response: Cytokines produced by T_{H 1} activates cells involved in CMI. The main cells activated are CD8⁺, macrophages and NK cells.

T_H2 response : Cytokines produced by T_H2 activates B cells. B cells poliferate and produce plasma cells and memory cells. Plasma cells produce antibodies. Cytokines also activates B- cells to class switch to different immunoglobulins according to the type of antigens.

Activation of T_C cells & function

T_C cells recognise peptides presented along class I MHC molecule . Thye also synthesis cytokinase, IFN - gamma. and TNF - beta ( Tumor necrosis factor - beta). The T_C cells get activated to form cytotoxic T lymphocytes (CTLs).

Mechanism of Action

I mechanism

After attachment to the target cells the cytotoxic T lymphocytes releases its content from the granules by a process called exocytosis. The major constituents of the granules are perforins and granzymes. Perforin polymerizes to form a transmembrane channel / pore in the target cell membrane. The granzymes are a set of serine protease. They pass into the target cell through the pores and indicate the apptosis of the target cells.

II mechanism.

Here the activated CTLs has Fas ligand which can interact with the Far receptor on the target cell. This interaction result in sequential activation of preoteolytic enzymes called caspase inside the target cell. By this mechanism the CTLs can be kill all target cells expressing forgein antihen.