Immune Response to Fungus, Protozoa and Metazoa Flashcards
What are fungal parasites? Include example
They are organisms that are saprophytic (they secrete enzymes that digest their food extracellularly before they absorb the nutrients)
Candida albicans
What are metazoans? Include an example
They are monophyletic parasites that are generally in the form of worms
Round worm (Wucgereria bancrofti)
What are protozoans? Include an example
Protists are anything that are eukaryotes but not an animal, plant, or fungus. They are not monophyletic, they are polyphyelic. Non-photosynthetic protists are called protozoa.
Amoeba
How do parasites enter the cell?
Parasites enter the host cell through ingestion or penetration through epithelial barriers
What does the parasite do once it has entered the host?
Sneak a mate in in order to produce eggs
Why does the immune system not rely on phagocytosis?
Parasites are typically too large to be enveloped
How does the immune system deal with parasites initially?
It relies on excretory/secretory antigens to become activated
Where are excretory/secretory antigens from?
They are typically intestinal content from parasites or uterine content from female eggs
What detects these antigens?
Mast cells
What happens after antigens are detected
Mast cell degranulation occurs, releasing histamine which increases blood flow and vascular permeability at the site of infection
What do dendritic cells do with antigens?
Internalise and process them and present them on their MHC II receptors
Where do dendritic cells migrate to?
Lymph nodes
What happens at the lymph nodes?
Dendritic cells present antigens to naive T cells which activates them and drives them to differentiate into Th2 cells
What is the role of Th2?
Cause B cells to become plasma cells which produce antibodies such as IgE and IgG
What cytokines do Th2 cells release and what do they do?
IL-5 which drives eosinophil proliferation
What do eosinophils release?
IL-4 which can generate more Th2 cells in a positive feedback loop
What do IgE antibodies do?
Bind to the parasite surface and then eosinophils bind to IgE using their FCR1 receptors, which signals the eosinophil to kill the organism bound to the antibody
How do eosinophils kill the parasite?
Degranulation, includes potent anti-parasitic proteins that damage the parasite and ultimately kill it
What is the first line of immune response against fungi?
Epithelial barrier that provides protection by excluding microbes and removing them physically
How do we recognise fungal danger signals?
PAMP-pathogen associates molecular pattern on fungi
PRR-pattern recognition receptor on cells
What is the epithelial response to fungal danger signals?
Produce antimicrobial peptides like protease inhibitors, enzymes, binding and neutralising proteins, and cytokines and inflammatory mediators which recruit macrophages and dendritic cells to the site
What are 3 pattern recognition receptors expressed by dendritic cells?
Toll like, C-Type lectin and NOD-like receptors
How do dendritic cells respond to spore antigens as opposed to hyphal antigens?
Spore-induce IL12 resulting in a Th1-type immune response
Hyphal-IL4 and IL10 which leads to a Th2-type immune response and induce IL1 beta production
What happens when IL1 beta is produced?
IL17 is produced which recruits neutrophils to the site of infection which phagocytose fungi and stimulate the production of peptides called defensins that target fungal hyphae
What happens when IL1 beta is produced?
IL17 is produced which recruits neutrophils to the site of infection which phagocytose fungi and stimulate the production of peptides called defensins that target fungal hyphae
What is a Th1 type adaptive immune response?
Enhances the functions of phagocytic cells via the production of INF-gamma
