10/27 Immunology Intro Flashcards
what is the central lymphoid organ located in the superior mediastinum?
the Thymus
what happens to insure that our T cells work properly? that the TCR of T cells does see MHC
development in the thymus that includes two selective steps
what is MHC?
major histo-compatability complex
what type of organ is the thymus?
it is a lympho-epithelial organ
what is a lympho-epithelial organ?
epithelial reticular cells make a cellular reticulum that induces lymphocyte progenitor cells to beome pre-T cells and supports the development of T cells. (no extracellular fibers!)
what is in the thymic cortex?
no extracellular fibers but macrophages and related bone marrow cells are present.
why would it be difficult to find the thymus in an elderly patient?
The thymus is well developed at birth but then involutes and shrinks after the first year of life.
what if you remove the thymus of an adult?
there is no serious consequences.
Outer skin of the thymus
the thymus is covered with a thin capsule which runs into organ forming septae (not trabeculae) and divides the organ into lobes and lobules.
how is the organization of the kidney and the adrenal similar to the thymus?
It is organized into a cortex and a medulla.
How can a microscope section of the thymus be divided into the cortex and medulla?
the cortex is just under the capsule and is darker staining cells that are closer together than in the medulla. The dense is the cortex and the not so dense is the medulla
describe the cells of the thymic cortex!
small little lymphocytes (T cell lineage); spidery epithelial reticular cells; large vaculoe filled macrophages.
the prominate corpuscle in the thymic medulla
small hassall’s corpuscle
the invaginations of the capsule in the thymus
septum!
specialized endothelial cells..that are vessels that are easy for lymphocytes to get in and out of from the blood.
High endothelial venule (HEV)
how can we identify the thymus based on the contents of the medulla (esp. old thymus)?
they have very large hassels corpuscles!
how do we have a blood-thymus barrier
epithelial reticular cell that is wrapped around the capillary. This is found in the Cortex!!!
why do we have a blood-thymus barrier
keep antigens out of the cortex
describe the T cell development
the progenitor stem cells come from the bone marrow and circulate and come in by the HEV and into the medulla and move to the cortex, encounter epithelia cells and become thymocytes, or Pre-T cells. the TCR gene rearrangements occur and TCR is selected and expressed as well as both CD4 and CD8 - move towards medulla and contact with reticular cells, dendritic cells, and macrophages, antigen presenting cells that only present self and if they interact not so strong and not too weak with either a CD4 or CD8 they become that CD4 or CD8. (positive selection) Then into the medulla, it will interact with self antigen presenting cells and if they interact strong they are destroyed (negative selection) then they are successful naive cells and they leave again via the HEVs in the medulla
Does the pre-T cells’ TCR bind properly (moderate afffinity) to host MHC expressed on epithelial reticular cells.?
if no: the cell apoptosis and die; If yes: cell recieves supportive cytokine signals, and becomes a single positive cell (CD4 or CD*) and lives
what is a double positive T cells?
they hvae both CD8 and CD4