Tissues and Organs of Immune System Flashcards
1
Q
What is the lymphoid system and lymphocytes
A
- System consisting of lymphatic vessels, lymph nodes, and lymph
- Drains excess tissue fluid from extracellular space, nodes provide sites for immune surveillance
- Arranged in either discrete encapsulated organs or diffuse lymphoid tissue
- Lymphocytes: Major effector arm of adaptive immune system and rely on specific niches during their lifetime
2
Q
What are the primary lymphoid organs
A
- Site of lymphocyte development and differentiation
- Site for negative selection of self-reactive cells (BM / thymus)
- B lymphocytes develop in niche of bone marrow
- T cell precursors (CLP) develop initially in bone marrow, but then migrate to the thymus to achieve full maturity
3
Q
What are secondary lymphoid organs
A
- Site of induction of Ag- specific immune responses
- Encapsulated organs (spleen, lymph nodes, MALT)
- Immune response is initiated
- Areas where mature lymphocytes encounter antigen, become activated, undergo clonal expansion and differentiate into effector cells
- T-cell and B-cell activity are separated into distinct micro-environments
- Cells actively migrate toward each other during activation events for their required interactions
- Lymphocytes migrate to and function in the secondary lymphoid organs
4
Q
Describe structure of the spleen
A
- Red Pulp: Venous sinuses and cellular cords containing resident macrophages, erythrocytes, platelets, granulocytes, lymphocytes and plasma cells
- White Pulp: WBC reside
- Marginal Zone: APCs (metallophilic MØs, MZ MØs, DCs), MZ B cells (distinctive phenotype IgMhi IgDlo) and B1 cells (produce low affinity / natural Abs)
- Vascularisation: Central arteries / venous sinuses
5
Q
What are germinal centres of the spleen
A
- Contain activated B cells, follicular DCs (FDCs), T follicular helper (Tfh) cells and phagocytic macrophages
- FDCs present Ag to B cells in the spleen
- Site of B cell differentiation
- Produce short lived antibody producing plasma-blasts and long lived plasma cells
- Site of somatic mutation and isotype switching for B cells.
6
Q
What is the function of the spleen
A
- Clearance of microorganisms and particulate antigens from blood stream
- B and T cells migrate through via periarteriolar lymphocyte sheath (PALS) and enter BV in MZ and red pulp
- Synthesis of IgG
- Removal of abnormal red blood cells (RBCs)
7
Q
Describe the structure of lymph nodes
A
- Occur at lymphatic branches
- Surrounded by collagenous capsule
- Trabeculae and radial fibres provide support
- Cortex: B cells in primary and secondary follicles
- Para-Cortex: T cells, interdigitating cells, high endothelial venules, migrate to GC in response to chemokines and become Tfh
- Central Medulla: Organised into cords, separated by sinuses, origin of efferent lymphatic vessel, T and B cells, plasma cells and macrophages
- Subscapular Marginal Sinus: B cells, similar to MZ B cells in spleen, intercept incoming pathogens mounting a rapid IgM T-independent response
8
Q
What is the function of the lymph nodes
A
- Protect the body from Ags that come from the skin or internal surfaces and are transported by lymphatic vessels
- Responses to Ags encountered leads to Ab production andcell mediated immune responses
- Both B and T cells develop into long-lived memory cells in secondary lymphoid tissues
9
Q
What are the types of mature lymphocytes
A
- T Lymphocytes: CD4+ T cells differentiate into Th (assist B-cell response) and CD8+ T cells differentiate into Tc (attack and destroy virally infected cells
- B Lymphocytes: Mature in GC, antigen affinity increased via somatic hypermutation, class (isotype) switching
10
Q
What are the germinal centres of the lymph nodes
A
- Form in secondary follicles following Ag challenge with a T-dependent Ag
- Surrounded by a mantle zone of lymphocytes
- Mantle Zone B cells co-express surface IgM, IgD & CD44 (naïve cells)
11
Q
What is the location and function of MALT
A
- Mucosa associated lymphoid tissue
- Lamina propria and submucosal areas of GI tract, lungs and genitourinary
- Protects mucosal surfaces
- Specific homing (lymphocytes express homing molecules, attach to adhesion molecules)
- ## Organises responses to antigens that enter mucosal tissues
12
Q
Describe the structure of MALT
A
- Network of follicles and lymphoid micro-environments associated with intestines (GALT)
- Contain DCs for uptake, processing and transport of Ags to draining LNs
- Capsulated and non-capsulated tissue
13
Q
What are peyers patches in MALT
A
- Found in lower ileum of GI tract
- Overlying epithelial layer (follicle associated epithelium - FAE)
- FAE facilitate transport of Ags to lymphoid tissue below, contain M cells
14
Q
What are M cells in MALT
A
- Specialised cells
- Deep invaginations on surface
- Basolateral membrane pockets contain T / B cells, DCs and macrophages)
- Ags and microbes are transcytosed into pocket and picked up by DCs
- Deliver antigen from intestinal spaces to lymphoid cells in gut wall
15
Q
What is the role of cell adhesion molecules (CAMs)
A
- Expressed on cell surface
- Involved in binding with other cells or with the extracellular matrix
- Aid leukocytes in adhering to the vascular endothelium prior to extravasation
- Increase the strength of the functional interactions between cells of the immune system and their targets
