Mechanisms of Host Defense (Buxton) Flashcards
What type of cells make up innate defenses against extracellular microbes? What do they do?
Phagocyte - a cell (e.g. WBC) that engulfs and consumes foreign material (e.g. microorganisms) and debris
Complement - group of proteins in normal blood serum and plasma that in combination with antibodies causes the destruction especially of particulate antigens (as bacteria and foreign blood corpuscles)
What are the host defenses against extracellular microbes?
Innate defenses, antibody, CD4 cells
What cytokines do CD4 cells secrete against extracellular microbes? What do they do?
Th17 - helps induce neutrophil response (IL-17 causes more neutrophils to be produced in the bone marrow
Th2 - helps produce IgE (if dealing with parasite), also some other Ig
What are the host defenses against intracellular microbes?
Innate defenses, CD4 cells, CD8 cells
What types of cells make up innate defenses against intracellular microbes? What do they do?
NK cells - large granular lymphocyte capable especially of destroying tumor cells or virally infected cells without prior exposure to the target cell and without having it presented with or marked by a histocompatibility antigen
Macrophages - phagocytic tissue cell of the immune system that may be fixed or freely motile, is derived from a monocyte, functions in the destruction of foreign antigens (as bacteria and viruses), and serves as an antigen-presenting cell
What cytokines do CD4 cells secrete against intracellular microbes? What do they do?
Th1 - secretes IFN-γ and TNF-α, activates macrophages to kill microbes located within the macrophages’ phagosomes. Also activate cytotoxic T cells to kill infected cells.
How does the body rid itself of viruses via the immune system?
Innate - IFN-alpha (protects cells in immediate environment that haven’t been infected yet), NK cells
Adaptive - CTLs
What is the most important cell in recovery from viral infections?
CTLs (CD8 cells)
What type of cell provides protection from re-infection or infection following vaccination?
Neutralizing antibody
What does type I IFN do to Class I MHC molecules?
Upregulates expression of them so that CD8 cells recognize antigens from them
Describe the cytotoxicity of CD8 T cells.
Antigen recognition and conjugate formation - CTL activation - granule exocytosis (granules contain perforin that acts like MAC and allows for granzymes to enter cell) - detachment of CTL - target cell death
What does it mean to neutralize the virus?
Blocking virus-receptor reaction
What do vaccines do?
Stimulate production of memory B cells and plasma cells that will secrete appropriate IgG if exposed to that virus
A 5 y/o child develops bacterial otitis media due to Streptococcus pneumonia. If opsonins and neutrophils are mounted in defense by the child’s immune system, what are the opsonins?
IgG & C3b
A 57 y/o man develops bacterial pneumonia due to Legionella pneumophila. What is the most important defense mounted by the man’s immune system?
Th1 cells and gamma interferon
What determines the most important defense mechanism for an infection?
The type of infection - extracellular, toxigenic, intracelluar
What do you need to activate the complement system?
Presence of bacteria in the body
What are the basic steps of defense against extracellular bacteria?
Presence of bacteria - complement & IgG - opsonization & acute inflammation - neutrophils - phagocytosis
What should you be worried about with a patient who presents with neutropenia?
Extracellular bacteria or fungi because patient has little to no neutrophil production
What are the basic steps of defense against toxigenic bacteria?
Presence of bacteria - release of toxin - anti-toxin antibody prevents toxin binding to receptors of susceptible cell
What are the basic steps of defense against intracellular bacteria?
Presence of bacteria - infected macrophage - anti-bacterial Th1 cell releases gamma IFN to activate infected macrophage (enhances its killing ability) & cc-chemokines to activate mononuclear cells (granuloma formation)
What do mononuclear cells do to an infected macrophage that is unable to kill intracellular organisms?
Surrounds it, forming a granuloma
What are the immune responses to extracellular fungi?
Opsonins - complement, antibody
Phagocytes - neutrophils, activated macrophages (requires Th1 cells)
What are the immune responses to intracellular fungi?
Activated macrophages (requires Th1 cells to supply gamma-IFN)
What is the general host defense against parasites? What does it not work against?
IgE antibodies - not good for protozoans
What are the basic steps of defense against extracellular protozoa?
Presence of protozoa - complement & anti-parasite antibody - opsonization & blocking antibody - phagocytosis
What are the basic steps of defense against intracellular protozoa?
Presence of protozoa - infected macrophage - anti-protozoal Th1 cell secretes gamma-IFN to activate infected macrophage (enhances killing ability) & cc-chemokines to activate mononuclear cells
What are the basic steps of defense against helminths?
Presence of helminths - anti-parasite IgE - mast cell sensitization & degranulation - IL-5 secretion - production of eosinophils in bone marrow; chemotactic for eosinophils
Streptococcus pneumoniae, Staph aureus, GAS, and Haemophilus all evade phagocytosis in what way?
Anti-phagocytic capsule
How does Mycobacterium tuberculosis evade phagocytosis?
Prevention of formation of phagolysosome, escape from phagolysosome, resistance to lysosomal enzymes
How does Neisseria evade immune responses?
Lysis of secretory IgA
How do HIV, influenza, Trypanosoma brucei, and Neisseria gonorrhea evade immune responses?
Antigenic variation
How do HIV and dengue virus evade immune responses?
By enhancing antibody (opsonizes organism which is then phagocytosed by macrophages, within which the virus replicates
How do schistosomes evade immune responses?
Masking of pathogen antigens by host serum proteins
How does HIV evade immune responses?
Induction of immune suppresion
How do HSV, VZV, and Staph aureus evade immune responses?
By expression of surface molecules that bind the Fc region of IgG
How do HSV & VZV evade immune responses?
Interference with antigen presentation by preventing peptide loading into MHC-I
