Immunity to Microrganisms Flashcards
What is innate immunity?
numerous non-specific barriers to infection that limit entry of or aid in rapid clearance of microorganisms
What are some of the major types of innate immunity?
skin, pH barriers (stomach, vagina), flushing, lysozymes, phagocytes, complement
Describe skin as a barrier
barrier to infection and produces fatty acids toxic to some bacteria
Describe pH barriers
organs such as the stomach or the vagina are acidic leading to the destruction of bacteria
Describe flushing
Many epithelial surfaces are cleaned by ciliary action or flushing such as the urinary tract
What is lysozyme?
present in tears, nasal secretions, and saliva; destroys cell walls
What are phagocytes?
macrophages and neutrophils that act to phagocytize invading pathogens without specific immune recognition.
What is complement?
can be fixed on the surface of many bacteria and yeast due to alternative pathway activation; leading to opsination or direct lysis
Where are most bacteria killed?
inside phagocyte
How do neutrophils and phagosomes know what to engulf?
they have receptors for many bacterial constituents
What is the fate of most bacteria that enter the body?
Most are killed and cannot cause disease
For the bacteria that do cause disease, how dos this occur?
Bacteria have evolved to defeat innate host defenses
What enables bacteria to evade hosts?
Virulence factors
Give examples of some virulence factors
Surviving acidic environment of the stomach (salmonella typhosa), spreading factors, toxins that inhibit or kill immune cells, antiphagocytic capsules, proteins that block opsination, antiphagocytic factors, attachment to epithelium
What is protein A
Protein produced by staph aureus that binds to and blocks opsinizing activity of IgG
What is S. pneumonia’s prime virulence factor?
antiphagocytic capsule
What bacteria can survive the acid environment of the stomach?
Salmonella typhosa
How can bacteria survive the phagosome?
Survive the digestive enzymes of the phagolysosome or prevent the fusion of the lysosomes with the phagosomes
What is the primary adaptive immune response to bacteria?
antibody
How does antibody fight bacteria?
prevent attachement to epithelium (IgA)
trigger complement leading to increased opsinization or lysis
binding to antiphagocytic M proteins or capsules, preventing the antiphagocytic activity and acting as an opsonin
kill bacteria faster thru opsinization
neutralize toxins
neutralize spreading factors like tissue damaging enzymes
What happens to bacteria that survive in normal macrophages in the presence of activated macrophages?
killed by activated macrophages
What type of bacteria can survive in the phagosome?
facultative intracellular parasites
Can antibody help clear facultative intracellular organisms that live in the phagosome?
No, they can only help them enter the phagosome.
How are macrophages activated to kill microorganisms?
T-helper 1 response
When activating a macrophage doesn’t work what happens?
Cytotoxic T cell CD8 needed to kill the infected macrophage, releasing the bacteria to be eaten by immunocompetent macrophage
Which infections are most likely cleared by cell mediated immunity?
Listeria monocytogenes, mycobacterium tuberculosis, M. leprae
What is cell mediated immunity?
immunity transferred between cells, not serum
What cytokines are secreted by TH1 cells? What do TH1 cells do?
IL-2 and IFN-gamma; activate macrophages and B cells, opsonize antibodies such as IgG1
What do TH2 cells secrete? What do they do?
IL-4 and IL-5; general activation of B cells to make antibody
IFN-gamma and CD40 ligand
TH1; activates macrophages to destroy engulfed bacteria
Fas ligand/ LT
TH1; kills chronically infected macrophages and releases bacteria to be destroyed by healthy macrophages
IL-2
TH1; induces T cell proliferation to increase the number of effector T cells
IL-3 and GMF-CSF
TH1;induces macrophage differentiation in the bone marrow
TNF-alpha and LT
TH1; activates endothelium to induce macrophage adhesion and exit from blood vessel at site of infection
CXCL2
TH1; causes macrophages to accumulate at site of infection
Specific immunity is a function of
T cells
Non-specific killing is a function of
activated macrophages
What response is most important for clearing parasites?
T cell response
What is the role of cytotoxic T cells in parasitic infections?
rarely kill the parasite, but kill parasite infected cells
What is the most important mechanism of parasite clearance? Why?
Macrophage activation; parasites can survive in macrophages that aren’t activated, but are quickly killed upon their activation
What role does T cell dependent granulomata formation play?
Interaction with activated macrophages that accumulate and release fibroblast growth factors; walls off the pathogen from the host
How are eosinophils activated? what is their role?
T cells produce cytokines that cause infiltration and increased produciton of them; kill parasitic worms
what do eosinophils secrete to kill parasitic worms?
major basic protein
What type of reaction does IgM and IgG use to kill blood borne parasites?
complement mediated reaction
How can antibody neutralize some parasites?
block uptake in receptor
How can antibody act as an opsonin
enhances Fc and C3b mediated phagocytosis
What is the role of IgE
Very important to immune response to helminths; mast cells can kill them; may be opsonin for macrophages and eosinophils
What is antibody dependent cellular cytotoxicity? What cells are invovled?
Potent mechanism for destruction of some organisms; macrophages, neutrophils, eosinophils, and mast cells
What are the 4 ways parasites escape the immune response?
Inaccessibility, Avoidance of recognition, immunosuppression, surviving in macrophages
How do parasites become inaccessible?
Hide in host cells, exist in gut, form cysts
How can parasites avoid recognition
vary antigen express or pick up host antigen to appear like self
