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Lymphoid 2

Lymphoid tissue 2

What does the thymus develop from? The third pharyngeal pouch
What antibody is secreted by mucosa plasma cells? IgA
How is IgA secreted? It is transcytosed, taken up by a receptor and secreted on the opposite side of the lamina propria
True or False: In elderly people there would be more islands of lymphocytes in the thymus False: There would be only a few small islands of lymphocytes in it. Mostly adipocytes
Does the thymus have a capsule? Yes
What is the process of hypoplasia called? Involution, age dependent involution (process of hypoplasia of lymphocyte and infiltration by adipocytes)
Is there a hylum in the thymus? No. Unlike the lymph node and spleen which have one
What are ERCs? Epithelial Reticular Cells which is sometimes referred to as the stroma
Where are ERC's present in the thymus? In both the cortex and medulla
Do ERCs produce reticular fibers? No, they have branched cytoplasm but no reticular fibers
Are ERCs connective tissue? No, fibroblast derived
What type of junctions do ERCs contain? Desmosomes and tight junctions
What is in the medulla that is specific to the thymus? Hassall's corpuscle
What intermediate filament is in ERCs? Keratin
What do ERCs produce? Hormones but function is not clear
How does blood vessels come in? Through trabeculae septa
What does the blood vessels do once they enter? They will rapidly divide into capillaries and small arterioles
Is there a blood thymus barrier in the medulla? No, only in the cortex
What does the blood thymus barrier consists of? Of ERCs with their tight junctions and basal lamina. ERCs have their own basement membrane and eosinophilic extension joined by desmosomes.
What is MHC 2 involved in? Antigen presenting cells by dendritic cells
What are the antigen loading docks? where the lysosomal protein pieces are picked up by MHC 2 and loaded onto the surface of the MHC 2 molecules
What will the display of antigen do? Will activate developing and mature T cells, so mature T cells will circulate in the blood and they will be able to detect any defective cell by the MHC I molecule
True or false: MHC I and MHC II are involved in the selection of T cells in the thymus True
Where do T cells settle? They migrate to the outer cortex and settle in the subcapsular region
What special cells are in the subcapsular region? Nurse cells. they induce proliferation of thymocytes
Describe positive selection they migrate towards the medulla and either get CD4+ or CD8+ but never both
describe negative selection Delete self reactive T cells
What MHC complex does CD4 recognize? CD8? CD4=MHC II and CD8=MHC I
What kind of loading docks do MHC I have? Loading docks for cytoplasmic peptides that are the one generated by virus proliferation in the cytoplasm
What do MHC I do to the virus? They will pick up the pieces of the virus and then actually the peptides become an integral part of the MHC molecule
Where are MHC I expressed? In the surface of all body nucleated cells (Not in Red blood cells: not nucleated)
When will CD8 be lower? In healthy conditions, but infection information will induce the MHC I and express more antigens on the surface of most body cells
What marker do all T cells contains? T-cell marker CD3. 755 of the lymphocytes in the blood is CD3+
Name a lymphocyte that is part of the non-specific immunity that does not contain CD3 nor immunoglobulin Natrual killer cells (null cells)
What are cytotoxic T cells involved in? The removal of tumor cells
Describe the location of MALTs They sit underneath the epithelium, either in the lamina propria or most of the time they will extend into the submucosa
Where are MALTs found? In the tonsils, larynx and pharynx
Describe the Peyer's patches in MALTs Important in the generation of plasma blasts that can protect the entire mucosal surfaces not just the plasma blasts themselves. The primary inductive site for IgM secretion
Describe follicle associated epithelium Right below the follicle associated epithelium is a dome. there are HEVs around where the T cells would be
Where are peyer's patches known to occur? In the appendix and even respiratory tract associated nodules
Name the special type of cell found in follicle associated epithelium M cells which refers to the fact that they are membranous
What is present in the pockets of the M cells? Lymphoid cells. There will be dendritic cells, macrophage type cells. The basement membrane has hole in which allow lymphoid cells to go back and forth between the follicle and the pocket within the membranous cell
Do M cells have microvilli? No but they have microfolds
What do helper T cells secrete that stimulates B cells? Cytokines that stimulate B cells and they proliferate and make IgA type antibody
Where do IgA type antibody cells settle? In the lamina propria. they will be picked up by the epithelial cells in the basement basal side and trancytosed to the luminal side
What is the IgA called after it is transcytosed? Secretory IgA and it contains some of the Fc receptor wrapped around it. The secretory component prevents the proteolysis of IgA
What helps the process of transcytosis? Fc receptor alpha
True or False: IgA is highly glycosylated True. The glycosylation helps make a kind of biofilm over the glycocalyx over the brush border
True or False: Peyer's patches generate the IgA plasmoblasts within their nodules True
Where are antimicrobial peptides present in the jejunum? Near the crypt, the epithelium and the basal region of the crypt will have these sides with very eosinophillic granules
What is eosinophillia due to? Highly enriched arginine
Do MALTs have a capsule? Cortex and Medulla? No they have epithelium around them. No cortex or medulla
Do MALTs contain germinal centers? Yes, proliferation occurs here
Are HEV present in the MALT? Yes where the naive lymphocytes exist



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