Lymphoid Tissues (11) Flashcards
What are the primary lymphoid tissues?
- thymus
- bone marrow
- foetal liver
What happens in primary lymphoid organs?
Lymphopoiesis- producing lymphocytes: T, B and NK cells
Where is the B cell “repertoire” generated?
Bone marrow
Where is final maturation of B cells?
in peripheral tissues e.g. spleen
Where do immature T cells migrate to from the bone marrow (in order to develop)?
Thymus
What are the hallmarks of the adaptive immune response?
- specificity: provided by a vast range of unique T and B cell receptors
- memory: rapid expansion in response to secondary encounter
What is a T/B cell ‘repertoire’?
the range of genetically distinct BCRs or TCRs present in a host–> larger repertoire means more threats can be recognised
What is positive selection of T cells?
deleting cells whose TCR cannot recognise and receive signals
What are double negative T cells?
do not express CD4, CD8, or natural killer (NK) cell markers
What are double positive T cells?
express both CD4 and CD8
What is negative selection of T cells?
deleting cells that recognise self-antigens/ react against our own body by apoptosis
What is thymic involution?
shrinking of thymus with age–> change in structure and reduced mass, more fatty
What are the secondary lymphoid tissues?
- where lymphocytes interact w/ antigens and other lymphocytes
- interconnected via lymphatic system and blood
- spleen
- lymph nodes
- appendix
- mucosal associated lymphoid tissue
What are fibroreticular cells?
- type of fibroblast
- recruit and retain T cells
- produce chemokines e.g. CCL19, CCL21–> cause naive T cells to migrate
- produce IL-7 cytokine to promote T-cell survival
What are follicular dendritic cells?
- stromal cells in B cell zone of lymph nodes
- produce chemokine CXCL13, which cause B cells to migrate
- BAFF cytokine= B cell survival factor
What are the epithelial barriers?
- first line of defence against infection
- physical barrier
- connected to extensive lymphatic network e.g. Peyer’s patches
What are Peyer’s patches?
- gut associated lymphoid tissue (specialised 2y lymphoid tissue)
- found below epithelium of ileum
- receive antigen either directly from lymphatic drainage from lumen or from M cells
- follicles highly enriched w/ B cells and germinal centres
What is a germinal centre?
anatomically restricted site where B cells undergo affinity maturation and class switch recombination to generate v high affinity antibodies
What migrates in the lymph to and from secondary lymphoid organs?
antigens and lymphocytes
How do naive T cells undergo extravasation from the high endothelial venule into lymph node?
- L- selectin on naive lymphocyte engages CD34 on HEV–> selectin binding and rolling along
- LFA-1 integrin binds ICAM, allowing cell to migrate across endothelium into lymph nodes
Which cells migrate out of site of inflammation in the lymph?
dendritic cells, so they can present antigens
–> head to T cell zone of 2y lymphoid tissue to interact w/ T cells–> screen for complementary receptor
