Cells And Tissues Of Immune System

Question 1

What is primary and secondary lymphoid tissue?

Answer 1

Primary=
Thymus and bone marrow, where lymphocytes develop

Secondary= all other
Lymph node:
- ~300 in body
- more in gut (Peyer’s patches

spleen:
- coordinated responses to cells circulating in blood

Question 2

Outline granulocytes

Answer 2

• neutrophils (70-80% WBCs), eosinophils, basophils
• phagocytosis and killing
• short lived, recruited to tissue during inflammation
• polymorphonuclear- several lobe nucleus and cytoplasm with granules
• phagocytotic- granules produce hypochlorous acid
• follow chemokine gradients (from macrophages), change adhesion properties of neutrophils so they stick to vessel walls and burrow through

Question 3

Outline macrophages

Answer 3

• Called monocytes in blood(~10% WBCs)
• phagocytic but only in tissue (when fully developed)
• clear dead cells, drain blood- Kupfer cells (liver), spleen macrophages
• deal with bacteria that withstand neutrophil killing (eg TB)
• clear up cellular debris from blood vessels, every tissue has them
• failure of macrophages is likely cause of degenerative diseases (neurodegenerative)
• long lifespan- can live years

Question 4

Outline lymphocytes

Answer 4

• Leukocytes in blood (~25% WBCs) (2% of total)
• very long lived
• T and B subpopulations indistinguishable until stimulated
• T cells develop in thymus, B in bone marrow
• constantly recirculate between tissue and blood

Question 5

Describe a lymph node

Answer 5

• ~1cm, connected by lymphatics
• Afferent lymphatics have valves
• collagen fibre mesh work sieves fluid- slows fluid, gives time for cells to respond

Question 6

Outline lymph node function

Answer 6

Structured tissue for efficient drainage and cellular communication
• local microenviroments- T and B cell areas for differentiation
• reticular meshwork- reticular cells (fibroblasts) synthesise collagen and use it to make reticular fibre framework
• dendritic cell network (antigen presenting/accessory cells)- present antigens to T cells
• allows communication- cells can’t be attached in blood as it would clot

Question 7

Outline dendritic cells

Answer 7

• Sample antigen from environment and carry to lymph nodes
• interface between innate and adaptive- present antigens to T cells
• eg, Langerhan’s cell- present in all layers of epidermis and contain Birbeck granules (formation induced by langerin)
• long process to capture and display antigens