Lymphoid tissues Flashcards
Where do T cells undergo final development ?
Thymus
Where do B cells undergo maturation?
Bone marrow
What are the two types of immunity?
Specific and memory
What are the specialised receptors for T cells?
TCRs (T-cell receptor)
What are the specialised receptors for B cells?
BCRs (B-Cell receptors)
Where does the B-cell progenitor stage occur?
Bone marrow
How are B cell receptor variable regions form?
Multiple copies of V,D and J genes can be rearranged in different combinations, contributing to diversity
Distinct V and J genes
What genes are responsible for the heavy chains?
D genes
What happens to the BCR upon antigen recognition?
Somatic hypermutation occurs; resulting in antibody with greater affinity to the target, B cells will subsequently differentiation into plasma cells (antibody-producing).
Which enzyme is used to promote mutations in antibody variable region gene?
Activation induced cytidine deaminase (AID)
What does CD mean?
Cluster of differentiation, CD proteins specific to particular lymphocyte
What are primary lymphoid tissues?
sites where lymphocytes are produced, supporting lymphoid-progenitor cute, cells that mature into B and T cells (helper and NK)
THYMUS, Bone marrow and foetal liver
What is the primary site of haemopoesis?
Bone marrow
Which cells do HSC differentiate into?
Lymphoid and myeloid progenitor cells
Where does further maturation proceed?
In the periphery
Where is the B cell repertoire generated?
Bone marrow
Which factor stimulates increased white cell production during infection?
Granulocute-colony stimulating factor
What is the definition of a repertoire?
Range of genetically distinct BCRs, or TCRs, present in a given host (larger the repertoire, the greater the number of recognisable threats)
Where do the lymphoid progenitors migrate to for antigen-independent maturation?
Thymus gland
Which specific T cell marks develop within the thymus?
TCR, CD3, CD4/8 and CD2
What is positive selection ?
Identifies whether T cells have successfully rearranged their TCR⍺ locus, and are capable of recognising peptide-MHC complexes with appropriate affinity. Positive T bind to cortical epithelial cells expressing Class I, or Class II MHC (+ self peptides) with high affinity to provide a survival signal.
Which complexes are recognised by TCRs during maturation the Thymus gland?
Peptide-MHC complexes (Class I and II MHC + self peptides)
Which cells do positive T cells bind to?
Cortical epithelial cells
Which signal is produced upon high affinity binding during positive selection?
Survival signal
Where does negative selection occur?
Medulla thymus
What is negative selection?
Destroys T cells that bind too strongly to self-antigens expressed on MHC. Cells undergo apoptosis.
What is thymus involution?
Shrinkage of the thymus with age. This is associated with a change in structure and a reduced mass
What is linked with thymic involution?
T cell regression
What effect does T cell regression have?
Thymus declined output
What are secondary lymphoid tissues?
Where lymphocytes interact with antigens. Encounter of dendritic cells bearing antigens from peripheral tissues, differentiating into effector and memory cells that eliminate the antigen
What are the secondary lymphoid organs?
Spleen, lymph nodes, appendix, mucosal associated lymphoid tissue.
How are lymphoid tissues connected?
Interconnected by the lymphatic and circulatory system, exists as discrete organs (lymph nodes adenoids) or distinct regions within a tissue (spleen)
How do the secondary lymphoid organs in regards to encountering the antigen?
Enables cells to become in close proximity to antigen.
Which cells sample the lymph?
Macrophages
What is the purpose of macrophages in secondary lymphoid tissues?
Presents the antigens to T and B cells during T cell activation (Humoral response)
Which cells in the lymph nodes produce chemokines?
Fibroreticular cells (fibroblasts)
Which chemokines are produced produced by fibroreticular cells?
CCL19, CCL21
What effect does CCL19 and ccl2 have on TCRs?
TCRs with integrated CCL7 encouraged to T cell zones of secondary lymphoid tissue- stimulates T cell migration
What do lymph nodes do?
Antigen presenting pathogens to be entrapped for T cells to activate and develop immune response against the specific antigens (Lymph nodes filters blood)
What zones include in the spleen?
Distinct T and B cells
What is the function of the spleen?
Screens the blood for antigens
Which ring is formed that encircles the lingual tonsils, oral and nasal cavity?
Waldeyer ring
What are specialised lymphoid tissues in the gut?
Peyer’s patchers
Where are Peyer’s patches?
Attached to efferent and afferent limbs
Below the epithelium of the ileum of the small intestine
What happens at the general b centre?
Undergoes affinity maturation (antibodies have high affinity for antigens).
Patches exhibit germinal activity, generation of B cells and plasma cells producing somatically mutated gut anti-specific IgA antibodies
What antibodies are produced by plasma cells derived from gut associated b centres?
Anti-specific IgA
What purpose is performed by the anti-specific IgA?
Secreted into the lumen to organise and regulate the intestinal microbiota
Which cells are enriched within the follicle?
B cells, high frequency of germinal centres
What are germinal centres?
Anatomically restricted, where B cells undergo mutation and selection to generate high affinity antibodies
What function does activation -induced cytidine deaminase occur?
Promotes class switch recombination (CSR) and affinity maturation through somatic hypermutation Alters variable region to produce high affinity antibodies.
What type of barrier is the first line of defence in the gut?
Epithelial barriers
What is the recirculating time for Naiive T cells?
24 hours
How do Naive T cells migrate across?
High endothelial venues (HEV)
What cells activate Naive T cells?
Antigen-presenting dendritic cells
Which receptors do Naive T cells express?
CCR7 receptors, and adhesion molecules L-selectin & LFA-1
Which endothelial protein do L-selectins interact with?
Glycam-1 and CD34
What effects does CCL21 binding to CCR7 have?
Conformational change in LFA-1, thus tightly binds to ICAM-1, move through hEV by extravasation, trans-endothelial migration
Which complexes do antigen-persenting cells associated antigen peptides with?
MHCI/2
