A beneficial suicide

A group of scientists lead by Arturo Zychlinsky at the Max-Planck-Institute for Infectious Biology in Berlin, Germany discovered, how the neutrophils form this snaring network (Journal of Cell Biology, online, January 8, 2007).

Once triggered, the cells undergo a novel program leading to their death. While they perish, the cells release the content of their nuclei. The nucleic acid, mingled with bactericidal enzymes, forms a lethal network outside the cell. Invading bacteria and pathogenic fungi get caught and killed in the NETs.

Every minute, several million neutrophils leave the bone marrow and are ready to defend the body of invading germs. They are the immune systemâ€TMs first line of defence against harmful bacteria and migrate into the tissue at the site of infection to combat pathogens. For more than hundred years it was known that neutrophil granulocytes kill bacteria very efficiently by devouring them. After eating the germs neutrophils kill tehm with antimicrobial proteins.

The group of scientists lead by Arturo Zychlinsky at the Max-Planck-Institute for Infectious Biology discovered a second killing mechanism: neutrophil granulocytes can form web-like structures outside the cells composed of nucleic acid and enzymes which catch bacteria and kill them. The scientists were able to generate impressive micrographs of these nets. But it remained a mystery how the granulocytes could mobilise the contents of their nuclei and catapult it out of the cells.

Only after lengthy live cell imaging and biochemical studies it became clear how neutrophils make NETs. The cells get activated by bacteria and modify the structure of their nuclei and granules, small enzyme deposits in the cytoplasm. "The nuclear membrane disintegrates, the granules dissolve, and thus the NET components can mingle inside the cells", explains Volker Brinkmann, head of the microscopy group. At the end of this process, the cell contracts until the cell membrane bursts open and quickly releases the highly active melange. Once outside the cell, it unfolds and forms the NETs which then can trap bacteria.

Surprisingly, this process is as effective as devouring bacteria: "NETs formed by dying granulocytes kill as many bacteria as are eaten up by living blood cells", says Arturo Zychlinsky. Thus, neutrophils fulfil their role in the defence battle even after their deaths.

Citation: Tobias A. Fuchs, Ulrike Abed, Christian Goosmann, Robert Hurwitz, Ilka Schulze, Volker Wahn, Yvette Weinrauch, Volker Brinkmann and Arturo Zychlinsky, Novel Cell Death Program Leads to Neutrophil Extracellular Traps, Journal of Cell Biology, online published, January 8, 2007

Source: Max-Planck-Gesellschaft

Arteries from distinct regions of the body have unique immune functions
Human arteries play distinct roles in the immune system depending on their anatomical location, researchers at Emory University School of Medicine have discovered.
Innate immune system targets asthma-linked fungus for destruction
A new study shows that the innate immune system of humans is capable of killing a fungus linked to airway inflammation, chronic rhinosinusitis and bronchial asthma. Researchers at Mayo Clinic and the Virginia Bioinformatics Institute (VBI) have revealed that eosinophils, a particular type of white blood cell, exert a strong immune response against the environmental fungus Alternaria alternata. The groundbreaking findings, which shed light on some of the early events involved in the recognition of A. alternata by the human immune system, were published recently in the Journal of Immunology.
Going from ulcers to cancer
Researchers have uncovered a big clue as to why some of the bacteria that cause stomach ulcers pose a greater risk for serious problems like stomach cancer than others; it turns out these bacteria can exploit the surrounding stomach cells to protect them from the immune system.
Accumulated bits of a cell's own DNA can trigger autoimmune disease
A security system wired within every cell to detect the presence of rogue viral DNA can sometimes go awry, triggering an autoimmune response to single-stranded bits of the cell's own DNA, according to a report in the August 22nd issue of the journal Cell, a Cell Press publication. The source of that single-stranded DNA is so-called endogenous retroelements—genetic elements accounting for a substantial portion of the genome that can move to new locations using a "copy and paste" mechanism, according to the researchers.
Study on salmonella self-destruction
ETH Zurich biologists, led by Professors Martin Ackermann and Wolf-Dietrich Hardt, in collaboration with Michael Doebeli of the University of British Colombia in Vancouver (CN), have been able to describe how random molecular processes during cell division allow some cells to engage in a self-destructive act to generate a greater common good, thereby improving the situation of the surviving siblings.
Exploding chromosomes fuel research about evolution of genetic storage
Human cells somehow squeeze two meters of double-stranded DNA into the space of a typical chromosome, a package 10,000 times smaller than the volume of genetic material it contains.
Researchers discover how rheumatoid arthritis causes bone loss
Researchers have discovered key details of how rheumatoid arthritis (RA) destroys bone, according to a study published in the Aug. 22 edition of the Journal of Biological Chemistry. The findings are already guiding attempts to design new drugs to reverse RA-related bone loss and may also address more common forms of osteoporosis with a few adjustments.
Chemical liberated by leaky gut may allow HIV to infect the brain
In up to 20 percent of people infected with HIV, the virus manages to escape from the bloodstream and cross into the brain, resulting in HIV-associated dementia and other cognitive disorders. Now, scientists at the Albert Einstein College of Medicine of Yeshiva University have found strong evidence that a component of the cell walls of intestinal bacteria—a chemical present in high levels in the blood of HIV-infected people—helps HIV to penetrate the usually-impregnable blood brain barrier (BBB). The findings, published in the August issue of the Journal of Virology, could lead to strategies for preventing HIV from entering the brain and causing serious complications.

A beneficial suicide

Related stories:

News discussion: