Organs of the Immune System Flashcards
Where are lymphoid cells first produced?
in fetal omentum, liver and yolk sac
Where are lymphoid cells produced in adults and older fetuses?
bone marrow
What is bone marrow?
a hematopoietic organs that gives rise to all blood cells
Whata re the primary lymphoid organs?
bone marrow, thymus, Bursa of Fabricius in birds
What are the secondary lymphoid organs?
spleen, lymph nodes, unencapsulated lymphoid tissue, Peyer’s patches
Where do T lymphocytes mature?
thymus
Where do B lymphocytes develop and mature?
- Bursa of Fabricius (birds only)
- Bone marrow (primates and rodents)
- Intestinal lymphoid tissue (rabbits, ruminents, pigs)
True or false? primary lymphoid organs are usually sites of lymphocyte interaction with microbial antigens.
False - not unless there is an infection in the organs
What is meant when the thymus is said to undergo involution?
thymus is large in newborns but small to invisible in adults. Thymus has shrunken
What are the functions of the thymus?
- maturation of lymphocytes
- lymphocytes learn to differentiate foreign antigen from self antigen here
What happens to thymocytes with receptors that bind strongly to self-antigens?
destroyed through process calle apoptosis - negative selection
What happens if a thymocyte cannot bind any MHC II molecules?
they are also removed
What thymocytes are allowed to live?
the ones that recognize MHC II/Ag complexes with moderate affinity
- positive selection
What do the positively selected thymocytes do when they mature and leave to thymus as mature lymphocytes?
populate the secondary lymphoid organs
What regulates the maturation process of thymocytes?
a mixture of cytokines and thymic hormones such as thymosins, thymopoietins, thymulin, and thymostimulins
What is the Bursa of Fabricius similar to?
the thymus
What is the function of the Bursa of Fabricius?
antibody-forming cells mature and differentiate - negative and positive selection of B lymphocytes
What are secondary lymphoid organs divided into?
- encapsulated organs (lymph nodes, spleen)
- Non-encapsulated tissues (mucosal lymphoid aggregates)
When do secondary lymphoid organs develop?
develop in late fetal life and persist in adults
True or Fasle? Secondary lymphoid organs enlarge in response to antigenic stimulation.
True
What do secondary lymphoid organs contain? What do they do?
contain dendritic cells which trap and process antigens and later present these antigens to lymphocytes to initiate an immune response
What are lymph nodes?
- round/bean-shaped encapsulated organs that act as filters of lymph to trap antigens
What are the regions of the lymph nodes?
cortex (outer), medulla (inner) and paracortex (between the two)
Where are B lymphocytes found in lymph nodes?
in the cortex in what are called germinal centers surrounded by capsules
Where are T cells and Dendritic cells found in lymph nodes?
paracortex
What is the principle function of a lymph node?
to facilitate the interaction between antigen presenting cells (APCs) and antigen sensitive T and B lymphocytes
What is the spleen?
a large encapsulated organ found in almost all vertebrates
- structured by a network of connective tissue trabeculae
What two forms of tissue does the spleen consist of?
red pulp - blood filtering and RBC storage
white pulp - Where immune response occurs - rich in lymphocytes
What does the spleen do?
- filters blood for blood-borne antigens, cellular debris, and aged blood cells
- stores RBCs, platelets, recycles iron
What are peyer’s patches?
non-encapsulated lymphoid tissue located in the wall of the small intestines
(in ruminents, pigs, horses, dogs, and humans they are found in the ileum)
What do peyer’s patches contain?
densly packed lymphoid follicles containing only B lymphocytes
What are Mucosal-Associated Lymphoid Tissue (MALT)?
non-encapsulated lymphoid aggregates scattered throughout the surfaces of the body and make up a large portion of the total lymphoid tissue
What are some Mucosal-Associated Lymphoid Tissues (MALT)?
- Gastrointestinal-associated lymphoid tissue (GALT)
- Bronchial-associated lymphoid tissue (BALT)
- Nasal-associated lymphoid tissue (NALT)
- Conjunctiva-associated lymphoid tissue (CALT)
What are Innate lymphoid cells (ILCs)?
immune cells that belong to the lymphoid lineage but do not express antigen-specific receptors
- secrete high concentrations of cytokines that are implicated in innate immunity, inflammation, lymphoid tissue formation, and tissue remodeling
What are the groups of Innate lymphoid cells?
- Group-1 ILCs
- Group-2 ILCs
- Group-3 ILCs
What transcription factors do Group-1 ILCs depend on? What do they produce?
are under the control of the T-bet transcription factor and include NK cells and ILC1 cells. Secrete sytokines such as IFN-gamma, and TNF-alpha in response to intracellular pathogens
What transcription factors do Group-2 ILCs depend on? What do they produce?
rely on GATA-3 nd ROR-alpha transcription factors. Produce IL-5, IL-9 and IL-13 in response to extracellular parasite infections
What transcription factors do Group-3 ILCs depend on? What do they produce?
include lymphoid tissue inducer cells (LTi) and ILC3 cells, are under the control of the ROR-gammat transcription factor. produce IL-17 and IL-22. required for the development of lymphoid tissues
