Host Defenses Flashcards
Cells of the immune system
- Monocytes
- Granulocytes
- Lymphocytes
Monocytes
- Circulate In blood stream
- Attracted to inflamed tissues
- Phagocytic
- Differentiate into macrophages & dendritic cells
Granulocytes
- Cytoplams contains granules
Includes:
* eosinophils
* basophils
* neutrophils (phagocytic)
* mast cells (induce inflammation)
Lmphocytes
- T cells: helper, cytotoxic
- B cells: antibodies
Innate defenses
- Properties of the normal host
- Non specific
Innate defenses of skin and mucous membrane
Skin:
* Thick layer of dead cells
Normal microbiome
* competes for attachment sites and nutrients
* secretes bacteriocin
Antimicrobial substances
* fatty acids
* Lysosymes
* antimicrobial peptides (AMPs)
* Antibodies
Mucous membrane
* Secretes mucous that traps bacteria
Innate defenses of the airways
- Mucous membrane that traps bacteria
- Ciliated cells remove mucus and trapped bacteria
Innate defenses of tissues and internal fluids
- Complement system
- Phagocytosis
- Inflammation
Complement system
- Set of blood proteins
- Activation results in the formation membrane attach complex (MAC)
- Causes cell lysis of some Gram-negatives
- No effect on Gram positives
Complement system activation pathways
- Classical: Antibodies
- Alternative: Microbial cell wall components
Serum sensitivity
Test sensitivity to complement by exposing pathogens to serum
Phagocytosis: Steps
- Attachement of organism to the membrane of the phagocyte
- Ingestion (organism becomes enclosed in a phagosome
- Granules containing hydrolytic enwymes fuse zith the phagosome forming the phagolysosome
- Oxidative burst (production of ROS)
- Killing and digestion of the microorganism
Phagocytes
- Neutrophils
- Macrophages
Inflammation: Signs
- Redness
- Heat
- Swelling
- Pain
- Recruitment of immune cells to thje site of infection
- Increased concentration of molecules
Interleukin-1: Functions
- Increases movement of liquid from blood to tisses and causes inflammation
- Increases the concentration of immune cells at infection sites
- Increases the spacing between tissue cells to allow immune cells to enter tissues
- Activates phagocytes
- Acts on the thermoregulatory center of the brain and causes fever to limit the growth of pathogens
Fever
- macrophages sense the presence of endotoxins
- Production of Il-1
- Il-1 acts causes body temp to increas
- High T reduces growth of some pathogens
- Il-1 activates phagocytes and other cells of the immune system
- Causes inflammation
Adaptive defenses
- Induced by the infection
- Rely on the detection and response to foreing antigens
- Specific to pathogens
Cells of the adaptive immune system
- T cells
- B cells
- Antigen-presenting cells (APCs)
Antigen-presenting cells
Macrophages and dendritic cells
Major histocompatibility complex (MHC)
- Antigen present molecular complex
MHC I:
* Antigens from inside the cell
* Present on all cells
* Recognised by cytotoxic T cells
MHC II:
* Antigens processed in phagolysosomes
* Present on APCs and B cells
* Recognised by T helper cells
T helper cells:
* Activate B cells and macrophages carrying the specific foreing antigens
* Useful against bacterial pathogens
Cytotoxic T cells:
* Rekease perforins/granzymes that kill host cells carrying the foreign antigen
* useful against infection by viruses/intracellular pathogens
Interleukin-2
Produced by activated T cells
* Induces multiplication & differentiation into effector T cells and memory T cells
Activated macrophages
- increased phagocytic activity
- produce much higher levels of
hydrolytic enzymes
B cells
Produce antibodies
Activation of B cells
- The B cell displays its antibody on its surface
- Pick up the foreign antigen it recognizes
- Antigen is processed and displayed on its surface by MHC II.
- A T cell specific for the antigen recognizes this complex and produces Il-4
- IL-4 activates the B cells which multiplies and differentiates into plasma cells and B memory
cells
Plasma cell
- Activated B cell
- Produces antibodies
Interleukin-4
- Produced by helper T cells
- Activates B cells
Antibodies
- Group of related proteins - immunoglobulins
- Highly variable antigen binding site (Fab)
- Constant region (FC) binds to receptor on macrophages
Function of antibodies
- Activates complement
- function as opsonins which increase phagocytosis efficiency
- Bind to toxins which prevents binding of toxin to host cells
- Bind to adhesins which prevents adhesion of microorganism to host cells
Memory cells
Ensure that the immune response, following a second exposure to the same antigen, is faster and stronger
Aquired active immunity
Involves the production of memory cells in response to antigenic stimulus
* Natural: following infection
* Artificial: vaccination
Aquired passive immunity
Involves the acquisition of preformed antibodies
* Natural: placental transfer or colostrum
* Artificial: serum from an immune animal
Natural immunity
Explained in part by the incompatibility of the virulence factor with the genetics of a species
