Question

Study Guide: Topic 8 TCRs and Topic 9 Activation of Immunocompetent T Cells

1a) How do effector T cells leave the lymph nodes (role of molecules such as SIP and SIP

receptors)

1b) Having migrated out of the lymphoid tissues into the blood stream, how do effector T cells

leave the bloodstream and get into infected tissues where they can interact with and activatemacrophages?

2a) How are double-positive cells in the thymus converted to single-positive cells that express

either CD4 or CD8?

Answer 1

The T cell which normally present in thymus will mature and leave the thymus. Once the T cell activated it proliferate and differentiate in to an effector T cell. The activated T cell include cytotoxic T cells and activated T cell. The lymphnode structrure is one of the regulators of immune responses against the infection.

1a) Most of the effector T cell leave the lymph node for the detection of antigen at the surface of an Antigen presenting Cell and for the immune responses.T cell migrated from lymph node to the targeted organ.Lymph node obtain T cell scanning of potential Antigen Presenting Cell coming from the different tissues.All T cell doesnot provided the informtion to differentiate the specific from non specific.This  activated T cell regulate the mechanism and update the migration pattern and link them to other cells that have been triggered and that proper differentiation.Like S1PR1 shows that T cell from the low S1P to of the lymphoid organ to the high S1P of blood.

1b)When the T cell get activated some of the T cell get migrate to infected tissue and interact with it  because of the function of phagocytic cell such as macrophage and destroy the microbes.Some of the T cell still remain in lymphoid organ and microbial agents get responded with the help of B cells and the Bcell secrete antibodies which is secrete in the body and cover up the macrophages,targeting for efficient phagocytosis.

2a)Double-positive thymocytes are CD4+and CD8+. The T cell receptor contain CD4+ and CD8+ in which CD4 is helper T cell and CD8 is activated T cell.The CD8+ coreceptor bind to MHC class I and CD4+ bind to MHC class II.There results in  double positive cells change in to single positive cell by the upregulation of both CD4 and CD8+ and get the high affinity for survival signal.

Double positive cells are mainly found in cerebrospinal fluid.But in the case of thymocytes it contain Tcell receptor is not capable for binding with MHC classI or class II and that cause apoptosis.