Biology 446 Unsolved Problems in Cell Biology Sept 9, 2015

Macrophages: Are much smaller than most differentiated cell types, despite their name. They are a kind of white blood cell, but different from lymphocytes and granulocytes. They (And produce much of the damage to oligodendrocytes in multiple sclerosis)

They are also called "Monocytes" (when circulating in the blood), "Kupfer cells" (when in the liver), "Dust cells" (when in the lungs), "Osteoclasts" (when dissolving bone), and "Microglia" when embedded in brain tissue. It is not known for sure whether these are different cell types, or the same. "Foam cells" in atherosclerotic plaque are believed to be macrophages, with vacuoles full of cholesterol.

Osteoclasts have hundreds of nuclei per cell, form by fusion of macrophages, and are very large.
(Their large size is necessary for them to cover broad areas of bone surfaces, and keep the enclosed space acidic.)

Macrophage behavioral responses are the opposite of all other cell types in the following six ways.

Galvanotaxis : Osteoclasts and Macrophages crawl directionally toward the positive electrode.
Epithelia crawl toward the negative electrode; mesenchyme cells line up perpendicular.

Haptotaxis: Macrophages accumulate on hydrophobic substrata; all other cells "prefer" hydrophilic materials. (This may be why macrophages accumulate among the cells of artery walls.)

Rugophilia: Macrophages crawl preferentially onto roughened plastic surfaces.
All other cell types are strongly inhibited by fine-order roughness of solid surfaces.

Contact Inhibition: Cell-cell contact inhibits locomotion by most differentiated cell types.
Macrophages preferentially accumulate underneath fibroblasts.

Response to proteolytic enzymes: Every other cell type detaches & rounds up when exposed to trypsin. Macrophages flatten more in response to trypsin.

Response to poking with a micro-needle: Other differentiated cell types retract; Macrophages extend toward objects.

Please discuss possible causes of each of these behaviors.

Also try to invent medical implications (like how to reduce osteoporosis, atherosclerosis, & damage to myelin).

What additional behavioral responses should be tested, to find out if macrophages respond in an opposite direction? (For example, chemotaxis, movement toward wounds, alignment parallel to thin fibers, strength of traction exerted)


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