1. Pathogens release chemicals that attract phagocytes
2. Phagocytes have receptors to bind and engulf pathogens
3. Lysosomes fuse with phagosomes to digest pathogens
4. Phagocytes present pathogen antigens on their surface
Animal secondary defences
Lymphocytes (B cells and T cells)
B cells and T cells respond to specific antigens
T cells mediate cell-mediated immune response
Second line of defense
1. Pathogen stopped from getting in or destroyed
2. Specific response to particular shaped antigens
3. Involves B lymphocytes and T lymphocytes
4. B cells mature in bone marrow
5. T cells mature in thymus
T cells
Responsible for cell-mediated response
Cell-mediated response
1. T cell receptors bind to antigen on antigen-presenting cells
2. Tcells divide rapidly by mitosis (clonal expansion)
3. T helper cells activate B cells and macrophages
4. T memory cells retain receptor for future infection
5. T killer cells destroy infected/abnormal cells
Antigen-presenting cells
Cells that present non-self antigen on their surface, e.g. infected body cells, phagocytes that have engulfed pathogens, transplanted organ cells, cancer cells
T killer cell action
1. Release perforin protein
2. Perforin embeds in cell membrane and creates pores
3. Causes cell contents to leak out or water to enter, leading to cell death
Humoral response
1. T helper cells stimulate B cells
2. B cells rapidly divide (clonal expansion)
3. B cells differentiate into plasma cells and memory B cells
4. Plasma cells produce antibodies
Antibodies
Globularquaternary structure protein with variable region that binds to antigen
Antibody functions
Agglutination (clumping pathogens)
Opsonisation (marking pathogens for phagocytosis)
Antitoxin (binding to toxins)
Primary immune response
1. First exposure to pathogen
2. Takes days to produce enough antibodies
3. Causes symptoms as pathogen causes damage
Secondary immune response
1. Re-exposure to same pathogen
2. Memory B cells rapidly produce antibodies
3. Pathogen destroyed before causing symptoms
Active immunity
Immunity gained from being exposed to pathogen or antigen, either naturally or through vaccination
Passive immunity
Temporary immunity gained from direct introduction of antibodies, e.g. from placenta or breastmilk
Cells are labeled with unique proteins to enable self/non-self recognition