Immune Response To Parasites Flashcards
(28 cards)
How do hosts detect parasites?
Detection of non-self antigens by receptors on the surface of the host white blood cells.
What is the innate immune response?
It occurs in response to a broad range of parasites (non-specific). There is no memory involved, meaning that prior exposure to parasites doesn’t improve subsequent defence.
What is the adaptive immune response?
Highly specific host response to parasite antigens. It is the ability from the host immune system to maintain a small population of cells specific to a given parasite antigen, even when the infection is cleared. This allows for rapid and specific response to subsequent infections.
What do mononuclear phagocytes (white blood cells) do?
Recognise foreign antigens, and attack the structure bearing them. They can phagocytose the cell, or secrete toxic compounds in the attack.
What do neutrophil cells do?
They are attracted to and enter the infected tissue, engulfing and destroying the microbes found there. They die after ingesting the target material
What do eosinophils do?
Thy position themselves against the parasites body and discharge destructive enzymes to destroy the.
Recognise and damage large extracellular parasites (cytotoxic)
What are b-cells and t-cells?
Lymphocytes that have specific recognition of parasite antigens.
What are Tc (cytotoxic) cells?
Recognise antigens from intracellular parasites and kill infected cells.
What are Th cells?
Can divide and produce clonal populations of antigen specific cells, which release cytokines to activate other cells in the immune system
What are b-cells?
Antigen-recognising and release large quantities of antibody
What is the immunoglobulin antibody igM?
First immunoglobulin secreted in response to infection — stimulates phagocytosis and binds cells bearing the correct antigen together — secreted across the wall of the intestine, and thus active against gut parasites
What is the igG immunoglobulin antibody?
IgM is replaced by IgG after 4-5 days, activates cytotoxicity by macrophages, neutrophils, and eosinophils
What is IgA immunoglobulin antibody?
Secreted in bod fluids
What is IgE immunoglobulin antibody?
Bound to cells called mast cells - release histamines into surrounding tissues and stimulates cytotoxicity by macrophages and eosinophils.
What impact do histamines have?
They directly damage parasites or disrupt their environment by tissue inflammation, which is important in the defence against helminths, particularly worms that live in contact with the gut lining.
How do anti bodies affect parasites?
Can reach parasites in a range of locations in or on the host.
How do fish antibodies affect ectoparasites?
They can produce antibodies either via the blood the parasites feed on or the mucous in the fish
What physical protection do parasites have to escape host defences?
Cysts - sealed off from the host and the immune system.
Hosts form a fibrous capsule around the cyst.
What are examples of parasites living in immunologically privileged sites to escape host defences?
Eye lens, or parts of the central nervous system.
Migration through the host is risky, many parasites as adult phase settle in the gut where there are fewer immune defences.
How do parasites escape host defences by hiding and molecular mimicry?
Intracellular parasites can hide inside the host cells, so antigens aren’t exposed to host immune systems. Mainly protozoans - metazoans are too large.
- Many coat their with host tissues or disguise them with host antigens.
What is an example of a parasite that can escape host defences by hiding and molecular mimicry?
Schistosom mansoni:
- Absorbs hosts antigens soon after invading the human, and thus becomes invisible to the host immune system
- An immune reaction is often to late for detection, but will protect against subsequent infection
How do shistosoma mansoni produce host antigens?
Absorption of host antigens likely occurs via host low-density lipoprotein (LDL).
Parasites show rapid uptake of LDL - may gain host antigens this way.
What happens if parasites can change their antigens presented to the host?
It can stay one step ahead of the hosts immune system.
By moulting: Nematodes in rates
Rapid turnover of antigens within a single life stage - Trypanosoma
How does malaria escape hosts defences?
Antibodies bind to free sporozoites or merozoites, but they can no longer access them once the parasites enter the host cells.
Red blood cells do not expresses MHC molecules on their surface, so they can escape recognition by CD8+ T cells.
