Session 4 Flashcards
(28 cards)
What is a healthcare infection?
An infection arising as a consequence of providing healthcare
What are some implications of healthcare infections?
Longer LOS for patients, damage to healthcare providers reputation, costly to treat.
How can healthcare infections be treated?
Eradicate the pathogen, prevent clinical manifestation of the infection, prevent transmission of the infection, screen for infection on admission, ensure proper cleaning and hygiene procedures.
What are the 4 Ps of infection prevention and control?
Place, practice, patient and pathogen.
What are the key features of antigen presenting cells?
Strategically located to allow a good response, act to capture the pathogen, illicit an immune response against the pathogen, several types of APC to allow best response to be elicited.
Where are class I MHC molecules found?
In all nucleated cells.
What do class I MHC molecules present?
Peptides from intracellular molecules.
Where are class II MHC molecules found?
On dendritic cells, macrophages and B cells.
What do class II MHC molecules present?
Peptides from extracellular molecules.
What features of MHC molecules make them effective?
MHC genes have co-dominant expression so diverse genetic makeup from both parents; genes are polymorphic so several different MHC molecules are created from the MHC genes.
Briefly describe the structure of MHC molecules.
Attached to the cell membrane; peptide binding cleft present with highly polymorphic residues for peptide to present to; class I peptide binding cleft is between alpha1 and alpha2 domains, class II peptide binding cleft is between alpha1 and beta1 domains.
What cells do class I MHCs present peptides to?
CD8+ T lymphocytes.
What cells do class II MHC molecules present peptides to?
CD4+ T lymphocytes.
Describe the endogenous antigen processing pathway.
Virus enters the cell and is exposed to degradation by proteasomes; antigenic peptide is produced by degradation which enters the ER of the cell; in the ER it forms an MHC which migrates to the cell surface; presents to CD8+ T cells at the cell surface.
Where does the endogenous antigen presenting pathway occur?
In all cells.
Briefly describe the exogenous antigen presenting pathway.
Microbes enter the cell and are digested; endosomes containing the digested bacteria fuse with larger vesicles containing partially formed MHC molecules; bacterial proteins fuse with the MHC molecules and migrate to the cell surface; present to CD4+ cells at the cell surface.
In which cells does the exogenous antigen recognition pathway occur?
Antigen presenting cells.
How is the chance of a T cell recognising a microbe increased?
All peptides from one microbe are presented by different MHC molecules.
How are T cells activated?
Via costimulation: must bind to two separate receptors to cause activation.
What occurs in intracellular adaptive responses?
- TH1 CD4+ cells are activated which causes CD8+ cell activation to kill virally infected cells
- B cells are activated to produce antibodies
- Macrophages are activated to kill opsonised microbes
What occurs in extracellular adaptive immune responses?
TH2 CD4+ cells are activated to recruit several other cells:
- Eosinophils to kill parasites
- B cells to phagocytose pathogens
- Mast cells to cause local inflammation
- Neutrophils to phagocytose pathogens
What is the antibody response at first encounter with a pathogen?
Main antibody response is from IgM with little IgG present. Over time this is replaced with IgG.
What is the antibody response at second exposure to a pathogen?
IgG is much more abundant than IgM due to the isotope switch mediated by TH2 CD4+ cells.
What features of IgG make it more effective in a secondary response than IgM?
Faster, stronger, longer acting, higher affinity response.
