Cellular Pneumatic Tube
Nothing works without communication: the body cells constantly exchange all kinds of information and use different communication systems. The adjacent neighboring cell is contacted via gap junctions, nerve cells transmit electrical signals via synapses, and immune cells send chemical signals to their own kind. Apparently there is another way of communication: a pneumatic tube.
Immune cells are gossips. While still warm, they tell their colleagues about every contact they have with foreign bodies and ask for help in combating it. To do this, they use the chemical mail route: they release chemical substances, the cytokines, which travel with the bloodstream to the addressee. If the letter lands in the mailbox there - the corresponding surface receptor - the recipient unpacks her mail immediately, reads the message and takes the necessary measures to rush to the sender's aid.
However, immune cells are obviously not satisfied with chemical mail alone, they also communicate with each other via a pneumatic tube system. Simon Watkins and Russel S alter from the University of Pittsburgh discovered this hitherto unknown way of communication – as is so often the case in science – by accident.
The scientists overheard dendritic cells having a neighborly chat. This tree-like, branched cell type influences the cellular immune response via cytokines and destroys bacteria that have invaded the body. To do this, they stretch out small protuberances, so-called lamellipods, with which they grab their victims and transport them to the cell body. There they are then absorbed and then digested. The amazing thing is that the dendritic cells stretch their arms out to the invaders long before they have had direct contact with them - they must have received the information from somewhere that work is waiting for them.
Now Watkins and S alter wanted to find out how the phagocytes notice that food is ready for them. To do this, they cultured dendritic cells and fed them products from the bacterium Escherichia coli and observed whether the scavenger cells reacted. As an activation marker, they determined the calcium concentration, which rises very quickly as soon as a cell is activated.
The screen looked like flashing lights in a dark concert hall
(Russel S alter) What the scientists saw surprised them: a minute or two before the dendritic cells stretched out their arms to catch prey, they took up plenty of calcium – albeit not uniformly: some of them were particularly active, others again did not respond at all. The working cells were spread all over the place. Some were far (up to 100 microns) from where the stimulation solution was injected, but nearby cells showed no response.
Interestingly, when a cell was accidentally nudged with the pipette tip but no stimulant was released, calcium levels also rose - and again a cell here, a cell there went to work. Clearly, the curious distribution pattern of the active cells could not be attributed to the stimulating solution slowly diffusing and reaching the cells sequentially.
Watkins and S alter therefore assumed that the cells were connected to one another and exchanged information via some extensions. Gap junctions, which transmit calcium flux in many cell types, were out of the question. Because a substance that blocks these cell connections does not impair the information transmission of the dendritic cells.
These nanotubules allow cells that are far apart to communicate. If the cell culture dish were a city, the distance would be about four to five blocks
(Russel S alter) The immunobiologists then placed the cells under a high-resolution microscope and discovered fine tubes that connected the cells with one another – up to 75 of these nanotubules reached from one cell to another. When the researchers nudged a cell under the microscope with a micro-injection needle, it immediately produced calcium, and after a few seconds the scientists were able to observe how calcium flowed from the activated cell through one of the fine tubes to a cell connected to it above. One to two minutes later, the cell stimulated via the nanotubule developed its tentacles.
Accordingly, dendritic cells are connected to one another via fine tube-like structures, via which they can transmit information over longer distances to cells attached to them, like a pneumatic tube system. The cellular coffee gossip is therefore more complex than previously assumed.
