Cells and tissues of the immune system

Question 1

Tissues and organs of the immune system (Primary)

Answer 1

• Development and maturation of adaptive immune cells(lymphocytes)
• Bone marrow (B cells)
• Thymus gland (T cells)

Question 2

Tissues and organs of the immune system (Secondary)

Answer 2

• Mature lympocytes meet pathogens

- Spleen, adenoids, tonsils, appendix, lymph nodes, Peyer’s patches, mucosa-associated lymphoud tissue (MALT)

Question 3

Lymph nodes

Answer 3

• Strategically located around the body
• ‘Meeting place’ for immune cells
• Pathogensb from infected tissue sites are picked up by the dendritic cells and arrive at the closest lymph node.
• Circulating T and B lymphocytes enter the node and congregate at specific regions (cortex/paracortex)
• If they meet a matching dendritic cell, they are activated and proliferate
• Architecture and size of node changes in response to activation of lymphocytes.

Question 4

Cells of the innate immune response(Monocytes and macrophages)

Answer 4

• Monocytes circulating in the blood migrate to tissues where they differentiate into macrophages
• Alveolar macrophages: lung
• Histiocytes: connective tissue
• Mesangial cells: kidney
• Microglial cells: Brain
• Kupffer cells: Liver
• Osteoclast: Bone

Question 5

Cells of the innate immune response(Macrophages - Phagocytosis)

Answer 5

Ingestion and destruction of particles/microbes

• 1.Bacterium becomes attached to membrane evaginations called pseudopodia
• 2.Bacterium is ingested, forming phagosome
• 3.Phagosome fuses with lysosome
• 4.Lysosomal enzymes digest captured material
• 5.Digestion products are released from cell

Question 6

Cells of the innate immune response(Macrophages - antigen presentation)

Answer 6

• Activation of adaptive immune response
• MHC = major histocompatibility complex
• 1.Antigen presentation to cytotoxic T cells via MHC class I
• 2.Antigen presentation to helper T cells via MHC class II

Question 7

Cells of the innate immune response(Dendritic cells)

Answer 7

-Better APCs than macrophages because of lower degradation potential:
=Antigen preservation
-Antigen uptake in peripheral tissues(immature)
-Migration to lymph nodes and antigen presentation (mature)
-Activation of adaptive immune response, T cells

Question 8

Cells of the innate immune response(Neutrophils)

Answer 8

• Polymorphonuclear neutrophils (PMN)
• 95% of circulating granulocytes
• Short-lived
• Major component of pus
• First line of defence against invading pathogens
• Recruitment to site of infection by interleukin-8 (chemotaxis)
• Phagocytosis and release of antimicrobial factors

Question 9

Cells of the innate immune response(Eosinophils, basophils and mast cells)

Answer 9

1. Killing of parasites:
   - Target recognition via IgE
   - Degranulation and release of toxic contents (histamine, proteases)
2. Association with allergies (IgE):
   - Cytokine release –> inflammation

Question 10

Cells of the innate immune response(Natural killer cells)

Answer 10

• 5-10% of blood lymphocytes
• Cytotoxic granules
• Recognise and destroy ‘abnormal’ cells (virus-infected, cancers)
• Detection via lack of MHC class I molecules

Question 11

Cells of the adaptive immune response(B lymphocytes)

Answer 11

• Express surface-bound B cell receptor specific for particular antigen
• Following binding to antigen, B cells proliferate and differentiate into antibody-secreting plasma cells

Question 12

Cells of the adaptive immune response(T lymphocytes)

Answer 12

• Express T cell receptor specific for particular antigen:
  1. T helper 1 (Th1) cells help macrophages and digest pathogens
  2. T helper 2 (Th2) cells help B cells to produce antibodies
  3. Cytotoxic T cells kill virus-infected cells