Lecture 18 - Infection and immunity Flashcards
(32 cards)
what are the three factors that influence the immune response?
Microbial factors
Host factors
specific immune factors
what are some microbial factors that influence the immune response?
dose, virulence, type of organism, route of entry
what are some host factors that influnce the immune response
integrity of innate barriers
competence of adaptive immune system
genetic capacity to respond to a particular organism
what are the levels of barriers that micro-organisms must proceed through during infection?
- anatomic/physical barriers (epithelia)
- complement/antimicrobial proteins
- innate immune cells
- adaptive immunity
what kind of molecules do innate immune cells recognise?
common molecules on bacterial or viral surfaces such as lipopolysaccharide
what is an example of an innate immune receptor and its mechanism of action?
macrophages express toll-like receptors.
- TLR4 binds LPS from gram -ve bacteria and lipoteichoic acids from gram +ve bacteria
- then they secrete cytokines that signal to other immune cells, phagocytose or present antigens to T cells via MHC II
which cell type does humoral immmunity and which cell types does cell-mediated immunity?
B cell does humoral
T cell does cell-mediated
what is the main function of helper t cells
they help other cells respond, such as telling a macrophage to kill phagocytosed microbes
what gives the CD8+ cell to kill with absolute precision?
highly variable antigen binding region of the T cell receptor
what are the two types of CD4+ T helper cells?
TH1
TH2
Treg
what does a TH1 response do?
- promotes cytotoxic responses and inflammation
- immunity against viral and intracellular/ingested bacterial infection
what does a TH2 response do?
- promote some antibody classes such as IgE and allergic responses
- immunity against extracellular organisms, in particular helmiths
what does a Treg response do?
controls TH1 and TH2 levels
- dampens the response and prevents autoimmunity
what activates the classical complement pathway?
antibodies
what is the alternative complement pathway
as a back up plan just in case a response is needed
- C3 hydrolyses and binds to pathogen surface
what are the three main outcomes of complement activation?
- opsonisation
- chemotaxis
- cytolysis
how does the lectin pathway work?
Mannose-binding lectin and ficolins recognise and bind carbohydrates on the pathogen surface
- similar to TLR - recognises general features
where do the three complement pathways converge?
all pathways generate C3 convertase, which cleaves C3 into C3b (deposited on microbial surface) and C3a (released)
what molecule is the central component of the complement pathways?
C3
what does C3a do?
along with C5a, chemotaxis
what are the two major bacteria that resist opsonisation and phagocytosis through a negatively charged polysaccharide capsule?
streptococcus pneumoniae
haemophilus influenzae
what are the main mechanisms of bacteria resistance to immune mechanisms?
- capsule resists opsonisation and phagocytosis
- intracellular growth in immune cells
what is the main pathogen which avoids the immune cells by growing within them?
mycobacterium tuberculosis -> prevents fusion of the phagosome into the lysosome
what are the main innate mechanisms for antiviral responses?
Must have to recognise infected host cells (viruses require host cell to replicate and grow)
- interferons
- natural killer cells
