Biological complexity: immune cells reach infections (Introduction)

by David Turell , Wednesday, January 18, 2017, 17:46 (2866 days ago) @ David Turell

They travel in the blood stream, are attracted by inflammatory molecules and must leave the vessels to reach the tissue that is inflamed to be effective in the battle. How does the cell leave the vessel without making a leak of blood? It squeezes out:

https://cosmosmagazine.com/biology/watch-immune-cells-squeeze-through-blood-vessel-wall...

"A team from Israel and the UK watched different types of immune cell shimmy through a blood vessel wall. And instead of the blood vessel cells contracting to let them through, it appears immune cells squeeze their way through, breaking a few cell structures which are rapidly replaced.

"Thousands of immune cells, such as white blood cells (also called leukocytes), are nudging their way through your blood vessels each second. When a part of your body becomes inflamed, for instance, molecules signal for help to leukocytes passing by in the bloodstream.

"When they come across such a signal, leukocytes stop and slip between cells that line your capillaries called epithelial cells. Epithelial cells are tightly wedged together to form a physical line of defence. But the damage leukocytes leave behind is insignificant. How?

"Sagi Barzilai and Sandeep Kumar Yadav, both from the Weizmann Institute of Science in Israel, and colleagues decided to see what was going on.

" They stopped the contracting machinery of the epithelial cells but found leukocytes were still able to penetrate. "That was our big surprise," says Ronen Alon, also from the Weizmann Institute.

"So using other cellular tweaks and microscopy, they eventually saw the leukocytes used their nucleus (which harbours important genetic information and, in leukocytes, is particularly pliable) prodded by their own cell machinery to squeeze between cells.
The leukocyte extended a thin protrusion between endothelial cells – think of it as the salesperson's foot. As more of the cell squeezed through, eventually a lobe of the nucleus was squashed through too (our salesperson's leg).

"As the nucleus lobe deformed the surrounding cells, endothelial cell scaffolding called actin snapped and stress fibres stretched, signalling the cells to open the gap. The leukocyte's own internal machinery pushed the nucleus forwards until it – and the rest of the cell – popped through.

"The gaps were only four or five microns wide – the width of the nucleus – and any bits of broken actin was quickly and easily replaced.:

Comment: Responses to infectious attack must be immediate. The blood white cells act intelligently. But they are acting under intelligent instructions, not that they are innately intelligent on their own. I view bacteria the same way, because they are the progenitors in evolution of these cells in our bodies.