Lecture Four; Components of the immune system 2 Flashcards
List the primary and secondary lymphoid organs;
1) Bone marrow and Thymus
2) NALT SALT (Skin) BALT (bronchus) GALT (payers patches, appendix) Lymph nodes
Describe drainage of lymph into the blood
Rest of body -> Thoracic duct -> Left subclavian vein
Top right quadrant -> Right subclavian vein
Describe DC function in lymphoid organs;
DC take up antigens from the blood and present them to naive T and B cells.
During central tolerance what can happen if a B cell is self reactive?
Immunoglobulin/receptor gene can be rearranged and the receptor can be tested again. If it continues to self react then it is destroyed.
What is a lymphoid tissue?
A tissue in which lymphocytes are found
What are lymphoid tissues usually?
Lymphoid tissues are usually groups of follicles that are surrounded or encapsulated by specialised supporting tissues or membranes.
Describe B cell arrangement in lymph nodes;
B lymphocytes are localized in the follicles
Describe t cell organization in lymph noes;
T lymphocytes are more diffusely distributed in the surrounding paracortical areas
What is also found in B cell follicles?
Follicular DC that distribute antigens between neighbouring follicles
What happens if a B cell in a follicle becomes activated?
The rest of the B cells move to the edge of the follicle
What occurs at the center of some B cell follicles?
B cell follicles contain germinal centres where B cells undergo intense proliferation after encountering their specific antigen and their co-operating T cell.
Describe Th and B cell interplay.
B cell with antigen receives signals from Th (reassurance) which allows it to undergo proliferation
Describe B cell and its changing follicular structure in lymph nodes;
Primary follicle (naive B cells) - Activation of some B cells in presence of Th cells. Secondary follicle (has Mantle of naive B cells)
This forms a germinal centre
What happens in a germinal center?
Essentially describes the proliferation of activated B cells
- Can be divided into light and dark regions.
Starting in the dark region;
- activated B cell forms proliferating centeroblasts
- These undergo somatic hypermutation (receptors gain high affinity)
- These centerocytes migrate to the light center where they undergo negative selection, those that self react are phagocytosed my macrophages.
- Those that dont self react, differentiate into memory cells and plasma B cells.
What are some extra features of lymph nodes that were not mentioned previously;
- Medullary sinus
- Medullary cords (macrophages and plasma cells)
- Marginal sinus (surrounds lymph node)
Describe the spleen;
- Fist sized organ
- Collects antigen from blood
- Disposes of senescent RBC
Describe the spleens colouring
Mostly Red pulp
Lymphocytes surround the arterioles entering the spleen and form white pulp
White pulp inner region is the peri-arteriolar lymphoid sheath (PALs)
Whats in PALs?
Containing mainly T cells and the flanking region termed the B cell corona
What is GALT?
Git associated lymphoid tissue
Inc; Tonsils, appendix, adenoids, peyers patches in SI
What is the function of GALT?
To collect antigen from epithelial surfaces of the GI tract
Whats important about payers patches?
Most highly organised of these tissues
Antigen is collected by special cells called multifenestrated or M cells (uses trancytosis to collect antigens)
Gives some notes about the thymus and T cell development;
CLPs enter the thymus and undergoes thymic selection (+ive and -ive)
Describe thymic selection;
Two parts +ive and -ive selection ( you should know this by now)
1% thymocytes survive selection
Therefore thymus is significant for T cell proliferation and apoptosis.
Thymic epithelium plays a role in selection mediated by various cytokines
Describe the anatomy of the thymus
Capsule
Cortical epithelium
Hassals corpuscle
Medullary epithelium
Cells; Thymocyte precursors Dividing thymocytes Maturing thymocyte DC macrophage
