Dynamics of neutrophil migration in lymph nodes during infection

29 Sep 2008

Maristela Martins de Camargo and Marcia Triunfol

Source: Immunity (see original article or PDF)

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Citation: Chtanova T, Schaeffer M, Han SJ, van Dooren GG, Nollmann M, Herzmark P, Chan SW, Satija H, Camfield K, Aaron H, Striepen B, Robey EA (2008). Dynamics of neutrophil migration in lymph nodes during infection. Immunity (3): 487-496.

Many living things in Nature swarm. Birds flock, insects and bacteria swarm and fish form schools. The reasons why some species organize themselves in swarms are still debatable. Are they on a specific mission under a higher-level command centre? Is there one single leader that organizes the flocking or do they transfer the leadership among themselves? What is the advantage of swarming?

Now, one important component of the innate immune system has been added to the growing list of living creatures that organize themselves into flocks and swarms. It is the neutrophil.

Neutrophils represent a crucial component of the innate immune system, as they form the first line of defence in vertebrates. They are among the first cells that migrate to the infectious/inflamed tissue where they start defending the threatened tissue against the invaders by using their main weapon: phagocytosis. Neutrophils are essential to life and their lack is incompatible with vertebrate survival, as clearly demonstrated by immunodeficiencies in which patients devoid of functional neutrophils succumb to common bacterial infections within days of birth.

But how do neutrophils arrive at the infection site? How do they organize themselves? The work by Chtanova and collaborators found that, as in many other living things, neutrophils too form swarms. The authors also investigated the swarm formation by following their race to lymph nodes, where they seem to remove macrophages. To do so, the authors used a two-photon scanning-laser microscopy to track neutrophils movements within both intact and mice lymph node infected by Toxoplasma gondii.

The authors showed that neutrophils migrate in a coordinated fashion that resembles what they called a paparazzi-like behaviour. As such, a few pioneer neutrophils are triggered by the presence of an infectious agent. These pioneer neutrophils then form an initial cluster that attracts a wave of neutrophil migration. When this initial cluster is joined by a significant number of neutrophils, they all initiate a series of fast but organized movements that resemble those of swarms. Interestingly, neutrophils present a streaming behaviour that resembles that seen in the slime mould Dictyostelium, in which individual cells leave traces of chemoattractants that are sensed by surrounding cells. These cells form a head-to-tail migration pattern that moves back towards the swarm.

The authors suggested that what attracts additional neutrophils to the swarm is the neutrophil production of these chemoattractants, which work as a feedback mechanism that enhances swarm formation by attracting transient swarms formed by approximately 150 cells that join the main swarm forming a larger and central swarm.

Once in the infection site, neutrophils can phagocytise foreign organisms or they can release traps that contain microbicide products. The authors speculate that having swarms of neutrophils that reach the infection site might constitute a very effective system against infection by different types of pathogens.

Chtanova and collaborators discussed additional roles for swarm formation that would be worth testing experimentally to provide insights about the biology of this important cell defence mechanism of the innate immune system.

A series of moving images showing how neutrophils form swarms can be seen in the supplemental data available at http://www.immunity.com/cgi/content/full/29/3/487/DC1/.

Note: This article is published in a journal which is not open access. To see the full article a subscription to Immunity is therefore required. In some developing countries, readers who are based in institutions may be able to access it through the HINARI programme.