Defences Against Infection Flashcards
How do viruses enter the body?
Mucosa of Respiratory tract
GI tract
Wound
Insect bite
What is the definition of infection
Invasion and multiplication of organisms in body tissues causing local/systemic injury
How do viruses enter a cell?
Bind to specific cell surface receptors
How do viruses replicate?
Using cells organelles
Leads to multiple mutations
What methods do viruses use to survive?
Long latency periods before illness and death
Transfer during short acute illness
Infect several species
What are immune responses to a virus the first time it is encounter?
Infected non immune cells
Infected dendritic cells
Antigen presenting cells
How do non immune cells respond to viral infections?
Shows increased expression of class I IFN and IL-12 molecules caused by increased expression, degradation of viral DNA and inhibition of protein synthesis. This stimulates NK cells
What are the immune responses of infected dendritic cells?
Activation of CD8 cells via MHC I molecules
What is the response of APCs to viral infections?
Phagocytosis of infected cells, presents MHC II on surface, activates T helper cells which activates B cells, CD8 and phagocytes
What is the humoral (antibody) response to viral infections?
Prevent binding to cell receptors
Induce ADCC
Inhibit release of progeny virus
Neutralise post binding inside endosome
What are the early non specific responses to viral infection (5)
Fever Phagocytosis Inflammation NK cell activity Interferons
What are the cell mediated immune responses? (4)
Cytotoxic T lymphocytes
Activated macrophages
Lymphokines
ADCC
What is the immune response to extracellular bacterial infections?
Efficient at low bacterial numbers Predominantly neutrophils and macrophages Phagocytosis enhanced by opsonisers Toxin cleanup by Abs Lysis by compliment
What are the two types of intracellular bacteria?
Intravesicular: block merging of endosomes
Cytosolic: break out of endosomes
What are the main defence mechanisms against intracellular bacteria.
Cell mediated response
NK cell activation
Delayed type hypersensitivity
CD8 activation
What is the mechanism of cytotoxic T cell activation to intracellular?
Intracellular bacteria cause macrophages to apoptosis
Dendritic cells (DC) phagocytose apoptotic cells
Fragments are displayed
Activates T helper cells
What are the main immune defences against fungi?
Commensal microorganisms Anti fungal peptides pH NETs (neutrophil extracellular traps) by eosinophils and mast cells Direct lysis
What are the 3 fungal PAMPs?
Beta glucans (glucose polymers)
Mannans (mannose polymers)
Chitin (N-acetyl glucosamine)
How does the humoral immune response work against mycoses?
Toxin neutralisation
Prevention of adherence
Opsonisation
ADCC
What is the cell mediated response to mycoses?
Helper T cells release IFN gamma
Causes macrophage activation which increases phagocytosis
What are the problems with host defences against Protozoa?
The life cycle of Protozoa causes different responses
Has intracellular and extracellular forms
What are immune systems advantages over worms?
Worms are predominantly extracellular
What are the worms advantages over the immune system?
Has both intra and extracellular phases
How can a pathogen be identified by its structure?
Innate immune system interacting with PAMPs using PRR
