2 Lymphoid System Flashcards
What is an antigen?
It is a specific marker protein on a cell surface
- for recognition
What are the 3 main types of T cells?
- Cytotoxic (Killer) T cell
- Helper T cell
- Regulatory T cell
What is the Major Histocompatibility Complex (MHC)?
MHC is a collection of genes coding for MHC molecules
- on the surface of all nucleated cells of the body
Have a role in adaptive immunity. Two types:
- MHC1 - Found on all nucleated cells
> present normal self-antigens, abnormal/non-self pathogens to effector T cell - MHCII - Only found on macrophages, dendritic cells, and B cells
> they present abnormal/non-self pathogen antigens for initial activation of T cells
What is an Antigen Presenting Cell (APC)?
APC
- heterogeneous group of immune cells
- classical APCs: macrophages, dendritic cells, B cells
They have the ability to present antigens specifically for the purpose of activating T cells
- they process + present antigens for recognition by T cells
What is the immune system?
Defends the body against infectious organisms + pathogenic agents + non-infectious substances + transformed cells + products
What is the lymphatic system?
The morphological counterpart of the immune system
- group of cells, tissues, organs that monitor body surfaces + internal fluid compartments
What is lymphoid tissue?
It forms the basis of the immune system of the body
- it reflects the physiological role of the lymphatic system
What are the primary lymphatic organs?
Bone marrow
- T + B cell differentiation
- B cell maturation
Thymus gland
- T cell maturation
What are the secondary lymphatic organs?
+ what is its significance
Lymphocytes enter the blood or lymphatic vessels to colonise
- secondary lymphatic organs and tissues
- where they undergo final stages of antigen-dependent activation
Organs:
- Spleen
- Lymph nodes
- aggregation of lymphatic nodules
Describe the circulation of lymph throughout the body
- Blood capillaries (blood)
- Interstitial space (fluid)
- Lymph capillaries
- Lymph vessels
- Lymph nodes
- Lymph vessels
- Lymph ducts
- Subclavian vein
AND back into the blood capillaries (blood)
What is a lymph node?
It is a secondary lymphatic organ
- Lymph nodes filter lymph along the pathway of lymphatic vessels
- AND initiate an adaptive immune response to antigens
Describe the movement of lymph into the lymph node
Enters through AFFERENT (in) lymphatic vessel
Exits through EFFERENT (out) lymphatic vessel
Lymphocytes can + do travel in lymph vessels, but majority (90%) travel in blood stream
- They can enter the lymph nodes at the sires of HIGH ENDOTHELIAL VENULES (HEV) in the paracortex
- (they have cuboidal endothelia)
Describe the general architecture of the lymph node?
Outer layer - Cortex (2 parts)
- superficial (1st half)
- deep/paracortex
Inner layer - medulla
What cells are in the Cortical zone? (superficial cortex - outer)
B cells
What cells are in the Paracortical Zone (inner cortex?)
T cells
- this area contains the majority of APCs in the node
What cells are in the Medulla (most inner layer)?
- HIgh concentration of plasma cells
- also macrophages for cleanup or holding undigestable material
Describe the Connective tissue in the Lymph node?
- Capsule - outer layer - Dense CT
- Trabeculae - dense CT (invaginations)
- Reticular tissue - supportive mesh work:
> Reticular cells + fibres
> Dendritic cells
> macrophages
Where are the follicles located in the lymph node?
In the cortex
Describe the primary follicles found in the lymph cortex
In the absence of immune stimulation, the cortical lymphoid follicles exist as PRIMARY FOLLICLES
- which are made of small B cells (virgin B cells or recirculation memory B cells)
There is also fine meshwork or dendritic reticulin cell cytoplasm
Describe the formation of secondary follicles
structure, activation, function etc.
With antigenic stimulation
- antigen recognising B cells are stimulated to replicate and differentiate
- This converts the Primary Follicle to SECONDARY FOLLICLE or GERMINAL CENTRE (indicates B cell response)
The Inner layer is the germinal centre
The GC is surrounded by a mantle zone (MZ)
- of small lymphocytes
- and a control area with replicating follicular centre cells + differentiation progeny
Describe the significance of the Germinal Centre in the secondary follicle
The inner layer is Germinal Centre
- GC shows areas of B cell maturation, where some activated B cells die off
- others differentiate to majority plasma cells, some into memory cells
- once zoomed in, paler and larger nuclei show Follicular Dendritic Cells, where antigens are held and presented during maturation
Describe the events that occur in the lymph nodes’ follicles, once an antigen is being presented
Antigen presentation occurs in the paracortex (T cell area)
- leading to T cells activation and proliferation
Meanwhile, B cells have picked up the antigen in the follicle
- ingested it and move to the B/T cell zone interface (edge of 2 cortical layers)
The activated T and B cells meet at the B-T cell interface zone
- The T helper cell-specific for this antigen activates the B cell
- to proliferate and mature
The activated B cells move back into the cortex
- to proliferate and mature
- This results in the formation of the germinal centre
