2. Immune cells and organs Flashcards
Primary lymphoid organs
Where lymphocytes are produced and mature
Bone marrow
Thymus
Secondary lymphoid organs
Where lymphocytes can interact with antigen and with other lymphocytes
• Spleen
• Lymph nodes
• Mucosal associated lymphoid tissues (MALT)
What does Thymic output decline with?
Age
Total number doesn’t decrease
Production of new specificities decreases with age
What does the bone marrow do during infection?
Increases WBC production
What are swollen lymph nodes a sign of?
Infection
Why do all lymphoid tissues (except spleen) have HEVs?
For cells to leave circulation and enter lymphoid tissue
What is the Spleen composed of?
Red pulp-RBCs
White pulp- WBCs
What can the Spleen act as?
a filter for antigens in the blood
1st line of defence
Epithelium Mucosae and skin form a physical barrier Very large surface area HEAVILY DEFENDED BY THE IMMUNE SYSTEM MALT cutaneous immune system
Gut Associated Lymphoid Tissue
Villi with draining lymphatic vessels
Intraepithelial lymphocytes
Peyer’s patches- large aggregates of lymphocytes and follicles
Peyer’s patches
only found in gut
predominantly B lymphocytes
contain germinal centres during immune responses
Cutaneous Immune system
Dense network of immune system cells in skin
Many draining lymphatic vessels from skin
Lymphocytes in layers of skin itself
Langerhan cells- type of dendritic cell able to present antigens
How does the body ensure that the antigen meets lymphocyte with specific receptor?
Anatomical structure of immune system: lymphatic structure drains whole body and filters fluid through lymph nodes
Lymphocyte recirculation- lymphocytes recirculate to find their antigens
Recirculation
Naïve lymphocytes produced in 1° lymphoid organs.
Enter blood and peripheral 2° lymphoid tissues.
If encounter their antigen they become activated
If they don’t, they keep recirculating till they die.
Dendritic cell action
- Pathogen enters through mucosal surface
- Dendritic cell circulating captures pathogen
- Migrates in lymphatics to draining lymph node and tries to present antigen
- Appropriate cells need to get into lymph node to respond to it
Extravasation of naïve T cells into lymph nodes
- Naïve T cells roll along surface of endothelium with low affinity binding. Mainly Selectin binding to carbohydrates on proteins.
- When they reach HEV, receive chemical signals from chemokines. T cell changes conformation of integrin molecules on its surface -> high affinity binding form.
- Stop rolling, become ‘arrested’
- Can migrate through endothelium
Lymphocytes
Small cells with agranular cytoplasm and a large nucleus
Cluster of Differentiation (CD) markers
nomenclature for cell surface molecules
used to discriminate between cells of the haematopoietic system (and other cells)
All T cells express
CD3
60% T cells express
CD4
30% T cells express
CD8
CD4 T cells
T helper cells, regulatory T cells
Secrete cytokines
CD8 T cells
cytotoxic T cells
Lyse infected cells, secrete cytokines
T cells only recognise processed antigen presented at surface of another cell using TCR
Antigen is presented by an MHC molecule
Where are B Lymphocytes produced and developed?
Bone marrow
B cell receptor
Surface antigen receptor: immunoglobulin like molecule
B cell CD markers
CD19 and CD20
B cells express MHC Class II
Can present antigen to helper T cells
B cell effector function
Produce antibodies
B Cell antigen recognition
B cells recognise intact antigen free in body fluids (not presented by another molecule) or on cell surfaces
Use B cell receptor, a membrane anchored form of antibody linked to signalling subunits
Antigen Presenting Cells (APCs) function
present processed antigen (peptides) to T lymphocytes to initiate an adaptive immune response
APC examples
Dendritic cells (DC)
B lymphocytes
Macrophages (activated)
