What is the difference between a phagosome and a lysosome?
When phagocytosis fails
Although phagocytosis successfully destroys many pathogens, some are able to survive and even exploit this defense mechanism to multiply in the body and cause widespread infection. Protozoans of the genus
Leishmania are one example. These obligate intracellular parasites are flagellates transmitted to humans by the bite of a sand fly. Infections cause serious and sometimes disfiguring sores and ulcers in the skin and other tissues (
[link] ). Worldwide, an estimated 1.3 million people are newly infected with
leishmaniasis annually.
World Health Organization. “Leishmaniasis.” 2016. http://www.who.int/mediacentre/factsheets/fs375/en/.
Salivary peptides from the sand fly activate host macrophages at the site of their bite. The classic or alternate pathway for complement activation ensues with C3b opsonization of the parasite.
Leishmania cells are phagocytosed, lose their flagella, and multiply in a form known as an amastigote (Leishman-Donovan body) within the phagolysosome. Although many other pathogens are destroyed in the phagolysosome, survival of the
Leishmania amastigotes is maintained by the presence of surface lipophosphoglycan and acid phosphatase. These substances inhibit the macrophage respiratory burst and lysosomal enzymes. The parasite then multiplies inside the cell and lyses the infected macrophage, releasing the amastigotes to infect other macrophages within the same host. Should another sand fly bite an infected person, it might ingest amastigotes and then transmit them to another individual through another bite.
There are several different forms of leishmaniasis. The most common is a localized cutaneous form of the illness caused by
L. tropica , which typically resolves spontaneously over time but with some significant lymphocyte infiltration and permanent scarring. A mucocutaneous form of the disease, caused by
L. viannia brasilienfsis , produces lesions in the tissue of the nose and mouth and can be life threatening. A visceral form of the illness can be caused by several of the different
Leishmania species. It affects various organ systems and causes abnormal enlargement of the liver and spleen. Irregular fevers, anemia, liver dysfunction, and weight loss are all signs and symptoms of visceral leishmaniasis. If left untreated, it is typically fatal.
(a) Cutaneous leishmaniasis is a disfiguring disease caused by the intracellular flagellate
Leishmania tropica , transmitted by the bite of a sand fly. (b) This light micrograph of a sample taken from a skin lesion shows a large cell, which is a macrophage infected with
L. tropica amastigotes (arrows). The amastigotes have lost their flagella but their nuclei are visible. Soon the amastigotes will lyse the macrophage and be engulfed by other phagocytes, spreading the infection. (credit a: modification of work by Otis Historical Archives of “National Museum of Health&Medicine”; credit b: modification of work by Centers for Disease Control and Prevention)
Key concepts and summary
Phagocytes are cells that recognize pathogens and destroy them through phagocytosis.
Recognition often takes place by the use of phagocyte receptors that bind molecules commonly found on pathogens, known as
pathogen-associated molecular patterns (PAMPs) .
The receptors that bind PAMPs are called
pattern recognition receptors , or
PRRs .
Toll-like receptors (
TLRs ) are one type of PRR found on phagocytes.
Extravasation of white blood cells from the bloodstream into infected tissue occurs through the process of
transendothelial migration .
Phagocytes degrade pathogens through
phagocytosis , which involves engulfing the pathogen, killing and digesting it within a
phagolysosome , and then excreting undigested matter.
Fill in the blank
________, also known as diapedesis, refers to the exit from the bloodstream of neutrophils and other circulating leukocytes.
the study of living organisms and their interactions with one another and their environment.
Wine
discuss the biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles in an essay form
advantage of electronic microscope is easily and clearly while disadvantage is dangerous because its electronic. advantage of light microscope is savely and naturally by sun while disadvantage is not easily,means its not sharp and not clear
Abdullahi
cell theory state that every organisms composed of one or more cell,cell is the basic unit of life
Abdullahi
is like gone fail us
DENG
cells is the basic structure and functions of all living things
A scanning electron microscope (SEM) is ideal for situations requiring high-resolution imaging of surfaces. It is commonly used in materials science, biology, and geology to examine the topography and composition of samples at a nanoscale level. SEM is particularly useful for studying fine details,
