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Our "Great White Shark" is the Ultimate Filter

05 Feb 2010

"White Blood Cell Chases Bacteria... It is a neutrophil chasing Staphylococcus aureus". For more details see "how neutrophils work"* at the end of the post.

It's good practice to make clear any assumptions or definitions so here's a brief introduction to how white blood cells function:

The immune system, which responds to an invading pathogen, is an intricate system of defense mechanisms designed to block and destroy any foreign substance entering the body. It is made up of many cells, which help it to perform its function... White blood cells fight infections, and protect our body from foreign particles, which includes harmful germs, and bacteria.

The immune system is an example of a complex information filtering and processing system. It's intricate design, superb pattern matching, and cheap disposable resilience has evolved to enable our survival. The features I'm most interested in are the advanced filtering technique and dispersed nature of our white blood cells.

Filtering and Motive Abilities Combined

Work done by Ronen Alon and Ziv Shulman has shown tiny leg like structures that sprout from the white blood cell as it moves through tissue.

Rather than sticking front and back, folding and extending to push itself forward, the cell creates numerous tiny 'legs' no more than a micron in length - adhesion points, rich in adhesion molecules (named LFA-1) that bind to partner adhesion molecules present on the surface of the blood vessels. Tens of these legs attach and detach in sequence within seconds - allowing them to move rapidly while keeping a good grip on the vessels' sides.
Next, the scientists turned to the Institute's Electron Microscopy Unit. Images produced by scanning and transmission electron microscopes, taken by Drs. Eugenia Klein and Vera Shinder, showed that upon attaching to the blood vessel wall, the white blood cell legs 'dig' themselves into the endothelium, pressing down on its surface. The fact that these legs - which had been thought to appear only when the cells leave the blood vessels - are used in crawling the vessel lining suggests that they may serve as probes to sense exit signals.
The researchers found that the shear force created by the blood flow was necessary for the legs to embed themselves. Without the thrust of the rushing blood, the white blood cells couldn't sense the exit signals or get to the site of the injury. These results explain Alon's previous findings that the blood's shear force is essential for the white blood cells to exit the blood vessel wall. The present study suggests that shear forces cause their adhesion molecules to enter highly active states. The scientists believe that the tiny legs are trifunctional: Used for gripping, moving and sensing distress signals from the damaged tissue.

The closest macro analogy I can compare to white blood cell sensing is smell. Sharks have long used their fantastic smell to track miniscule concentrations of blood in water to find their prey. In a similar way, chemotaxins meet the surface of the white blood cells for coarse direction, and pseudopod extensions for zeroing in, guiding the white blood cell towards invaders (bacteria, etc). White blood cells are own little army of sharks.

Why should a dataminer/founder like myself care? The following question gets to the heart of my interest:
How can modern information tools better mimick our master filters?
Surface matching requires "information structures" as well as an internal database of patterns. A flow of information is also needed to cause the surface filters to interact with the information. Both coarse (hashing) and high fidelity solutions can work in tandem to help filter out noise.

Perhaps an even closer analogy, is security software. The same immune system principles can be leveraged to identify and eradicate invaders. There we seek intruder patterns which are being actively designed.

Notes*:
how neutrophils work:

Neutrophils are the most common granulocyte. They have segmented nuclei, typically with 2 to 5 lobes connected together by thin strands of chromatin which can be difficult to see; the cell may thus appear to have multiple nuclei. The nuclear chromatin is condensed into coarse clumps. Small numbers of immature neutrophils or band form neutrophils may be seen in a blood smear. These are incompletely segmented and often have a 'C-shaped' nucleus.

The cytoplasm of neutrophils contains three types of granule.

Primary granules are non-specific and contain lysosomal enzymes, defensins, and some lysozyme. The granules are similar to lysosomes. They stain aviolet colour when prepared with Wright's stain which is commonly used in studying the blood. The enzymes produce hydrogen peroxide which is a powerful anti-bacterial agent.

Secondary granules are specific to neutrophils and stain light pink ('neutral stain'). They contain collagenase, to help the cell move through connective tissue, and lactoferrin, which is toxic to bacteria and fungi.

Tertiary granules have only recently been recognised. It is thought that they produce proteins which help the neutrophils to stick to other cells and hence aid the process of phagocytosis.

Once in the area of infection neutrophils respond to chemicals (called chemotaxins which are released by bacteria and dead tissue cells) and move towards the area of highest concentration. Here they begin the process of phagocytosis in which they engulf the offending cells and destroy them with their powerful enzymes. Because this process consumes so much energy the neutrophils glycogen reserves are soon depleted and they die soon after phagocytosis. When the cells die their contents are released and the remnants of their enzymes cause liquefaction of closely adjacent tissue. This results in an accumulation of dead neutrophils, tissue fluid and abnormal materials known as pus.

References:
White blood cells
Wikipedia on White Blood Cells