When do the two types of specific immune response occur?
Humoral = bacterial infection
Cell-mediated = viral infection
How do cells become antigen-presenting cells?
Macrophages engulf pathogens, which are packaged into phagosome (phagocytic vacuole)
- Fuses with lyosyme containing digestive enzymes like lysozyme
- Lysozymes digest pathogen membrane, causing it to lyse (breakdown)
- Antigens bind to MHC complex, antigens projected onto cell surface
Describe process of humoral response
- Pathogens enter the body, engulfed by macrophage and becomes APC
- MHC complex binds to CD4 receptors on T-helper cells
- T-helpers release cytokines which activate B-cells
- B-cells undergoe clonal expansion —> into plasma and B-memory cells
What do plasma cells do?
~ produce many antibodies, specific to antigens, which bind to antigens and cause them to lyse
What do B-memory cells do?
Remain in blood to quickly produce antibodies if same pathogen arrives
What are antibodies?
Proteins made by B lymphocytes
Describe structure of antibodies
Made up of 4 polypeptides; two heavy chains and two light chains
- joined by disulphide bridges
- polypeptides have variable region and constant region
- hinge region in centre allows for flexibility
Describe three types of antibodies
- Opsonin = bind to antigens + act as markers for phagocytes, makes phagocytosis quicker
- Agglutinins = bind to antigens + cause clumping
- Anti-toxins = bind to toxins produced by bacteria; phagocytes then engulf these
