Immune Response to Parasites Flashcards
Give examples of non-specific defences.
skin
chemical secretions, including mucus, tears and stomach acid
inflammatory response
phagocytes
natural killer cells responsible for destroying abnormal cells.
Explain the inflammatory response.
When the skin is damaged, the external barrier to parasites is broken. Parasites may enter, and this triggers a localised inflammatory response. The wounded region becomes warmer and redder as small blood vessels dilate. This increases blood flow to the injured area, thus increasing the number of white blood cells, such as phagocytes, allowing a suitable defence or attack so that healing can begin.
Explain phagocytosis.
Phagocytes arrive at the site of infection and engulf parasites by enfolding their plasma membrane around the parasite. The parasite is then brought into the phagocyte in a vacuole. Phagocytes contain special organelles called lysosomes. These are filled with digestive enzymes. The lysosomes fuse with the vacuole, releasing the digestive enzymes and allowing the enzymes to digest the parasite.
Explain the role phagocytes have in specific defence.
Phagocytes also have a role in specific defence. Foreign antigens, previously engulfed by phagocytes, are pushed back out onto the surface of the phagocyte. The phagocyte then presents these antigens to lymphocytes, another type of white blood cell.
Describe how B lymphocytes work.
In response to the foreign antigens presented by phagocytes, B cells produce proteins called antibodies that are specific in shape to the antigen.
Describe how T lymphocytes work.
T cells work by destroying specific infected or damaged cells by bringing about apoptosis.
Explain clonal selection.
Clonal selection is process by which lymphocytes become amplified undergoing the process of mitosis.
Each type of lymphocyte divides and differentiates into two clones.
One clone becomes a plasma cell, working to combat the antigen and is therefore only short lived.
In comparison, the other clone lives significantly longer assuming the role of a memory cell.
What 3 ways are endoparasites able to succeed?
Endoparasites mimic host antigens, therefore remaining undetected by the host’s immune system.
Endoparasites are also capable of modifying the host-immune response, preventing the host from mounting an attack so the parasite remains alive.
Some parasites show a huge antigenic variation. This promotes a rapid evolution rate, and the parasite remains a step ahead of host immune cell clonal selection.
What is epidemiology?
Epidemiology is the study of the outbreak and spread of infectious diseases.
What is the herd immunity threshold?
The herd immunity threshold is the density of resistant hosts in the population required to prevent an epidemic.
