Immunology 2 Flashcards
Where do B and T Cells mature?
B cells mature in Bone marrow
T cells mature in Thymus
Where is the Thymus located?
In front of the heart
What is the Thymus?
A bi-loobed organ, that is the site of T cell maturation.
What two sections comprise the thymus ?
The Cortex (outer) The medulla (inner)
What separates the two lobes of the Thymus? (TradeCalais 🇫🇷)
The trabecalae
Detail the cortex of the Thymus
Tightly packed, high cell density
Consist of proliferating immature Thymocytes (from bone marrow)
It is the site of positive selection
What is positive selection?
Thymocytes are exposed to self-MHC (expressed on epithelial cells of thymus). If non-reactive then they are eliminated. If they are reactive they diffuse closer to the medulla.
Note: it is a good thing they react with MHC as this is needed in future
Detail the medulla (remember Hasan’s spot 👺)
Loosely packed with cells, fewer lymphocytes present
But higher population of mature Thymocytes
Hassalls corpuscles can be observed here
Site of negative (medusa) selection
What role do Hassalls corpuscles serve supposedly?
Might function as sites of clearance for dead/un selected Thymocytes
What is involved in negative selection of the medulla?
Dendritic and macrophages display self-antigens/peptides
If Thymocyte has too high an affinity with them then eliminated to prevent autoimmune effects
Those with intermediate affinity are selected
What is occurs when the gene (Jayne/ gene) AIRE is expressed in the medulla of the Thymus?
Thymocytes are presented with more complicated self antigens
What two MAIN classes of cells are found in the thymus?
- Stromal cells
2. Cells of hemopoetic origin
What two types of stromal cells exist in thymus
Epithelial thematic cells (nurse cells etc)
Dendrites and macrophages
When is the thymus most active?
During early stages of life, neonatal, adolescence. Not so much in adulthood
Where are double negative immature Thymocytes found in thymus?
Where are double positive immature Thymocytes found in thymus?
Where are single positive mature Thymocytes found in thymus?
Double ++ = cortex
Double – = lower cortex
Single += medulla
How do T cells acquire their unique TCRs?
Through genetic rearrangement in the thymus
Name the two primary organs of the lymphatic system
Bone Marrow and the Thymus
Name 7 secondary lymph organs
Lymph nodes, Spleen, Tonsils, Peyers Patches, Mucosal-associated Lymphoid tissue (MALT), Appendix, and Bronchus-associated lymphoid Tissue (BALT- in rats/rabbits) and INDUCIBLE BALT (iBALT- humans and mice)
Where are most lymphocytes activated?
In the lymph nodes. Where antigens are trapped and encounter lymphocytes.
How do antigens arrive in nymph nodes?
Via lymphatic vessels, where they arrive in the into the lymph node at the AFFERENT vessel
Where clusters are Lymph nodes found ?
At clusters of junctions of lymphatic vessels
In lymph nodes, where are B cells found and where are at cells found ?
B cells- Cortex
T cells - para cortex
What cells in the Lymph nodes display antigen/foreign peptides?
Dendritic cells and macrophages