Lymphoid organs & cellular traffic Flashcards
What are the 2 types of lymphoid tissue.
Primary (central) and secondary (peripheral)
What is primary lymphoid tissue?
Tissue where lymphocytes develop (produced, mature, secreted) e.g. bone marrow and thymus
What is secondary lymphoid tissue?
Tissue where lymphocytes are maintained and adaptive immune responses are initiated e.g. lymph nodes, spleen and MALT (mucosa-associated lymphoid tissue)
What are some examples of MALT
Tonsils, BALT, appendix, Peyer’s patches
Where are B and T cells produced and where do they mature?
Produced in bone marrow but T cells mature in thymus.
What are immune cell precursors
Haematopoietic SCs
What is a lymph node?
Bi-lobed organ lying over the heart and major blood vessels
What are the lobules separate by and what do they consist of?
Connective tissue trabeculae and contain cortex and medulla
What is a thymocyte?
Immature T cell which migrates from bone marrow to thymus
What is the site of positive selection
The cortex - tightly packed with cells containing immature, proliferating thymocytes
What is the site of negative selection
The medulla - loosely packed with cells containing more mature thymocytes
What are the 3 thymic epithelial cells involved in T cell development?
Epithelial nurse, cortical, medulllary
What is the site of lymphocyte activation by antigen?
Peripheral lymph organs
How do lymphocytes and lymph reutrn to the blood
Thoracic duct
How do antigens from sites of infection reach lymph nodes
Lymphatics
What does CD stand for?
Cluster of differentiation
What do T cells express?
Th - CD4 (class II) and Tc- CD8 (classI)
When do T cells lose expression of CD4 or CD8?
When they differentiate
What defines B cells?
CD19+
What do lymph nodes do?
Filter and trap antigen from lymph
What do the nodes consist of?
Cortex (B cell area), paracortex (T cell area) and medulla
How do T cells enter a lymph node?
Across high endothelial venules in cortex
What do T cells do?
Monitor antigen presented by macrophages and dendritic cells
What do T cells do if they don’t encounter an antigen?
Leave node in efferent lymph
What do T cells do if they encounter an antigen?
Proliferate and differentiate into effector cells
What do T cells have on their surface?
L-selectin, LFA-1 and chemokine recepotor
What binds to L-selectin
GlyCAM-1 and CD34 - causes rolling interaction
What is LFA-1 activated by?
Chemokines bound to ECM.
What does LFA-1 bind to?
ICAM-1
What is diapedesis?
When the lymphocyte leaves the blood and enter the lymph node
Where do antigens enter the lymph node from?
The afferent lymphatic
What is the germinal centre?
Transient structure of intense proliferation (B cells start proliferating when antigen enters)
What are lymphoid follices?
Initially loose network of follicular dendritic cells (FDCs) in region rich in B cells
How are FDCs different from conventional DCs?
Display antigen to B cells (cross link Ag with B cell receptors and form Germinal Centres)
What do lymphocytes recirculate between?
Bloodstream, lymph nodes and lymphatics
What is the largest secondary lymphoid organ
The spleen
BALT
Bronchus-associated lymphoid tissue
GALT
Gut-associated lymphoid tissue
Where are Peyer’s patches found?
In the intestinal lining
What is an M cell?
Specialised epithelial microfold cells that transport antigens into the lymphoid tissue
Where are intestinal lymphocytes found?
In organised tissues (peyer’s patches) where immune responses are induced OR scattered throughout intestine (epithelium and lamina)
HEV
High endothelial venule
