Reptilian cells at low temperatures: 
A key to extended human space travel?

That's where reptiles have the advantage over mammals. The phagocytic cells of the immune systems of reptiles can function at near freezing temperatures. A team of researchers from Drake University, Iowa State University and Des Moines University--Osteopathic Medical Center, with the assistance of a $30,000 Phase 2 grant from the Iowa Space Grant Consortium, has been trying to identify a mechanism to enable the immune systems of mammals to do the same thing.

Initiated by Dr. James L. Christiansen of the Department of Biology at Drake, the team has focused its efforts on a reptilian cell called the melanomacrophage (MM). "We haven't solved the whole mystery, but we're on the trail of a solution," Christiansen says. "We've discovered major differences between how reptilian and mammalian immune systems handle low temperatures," he explains. "The next question is why."

Christiansen and Dr. James Johnson at Des Moines University--Osteopathic Medical Center are continuing to collaborate on this research, while beginning a related project (also funded by the ISGC) on immortality in reptiles. Both projects are aimed at extending human life to make long-distance space travel possible.

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How it works:

In very simple terms, bacteria in reptilian MMs are taken into the cell and processed at low temperatures (as cold as 20 C), but at similar temperatures, mammalian macrophages seem unable to move bacteria beyond the cell membrane.

A compound called clathrin may hold the bacteria inside the cell membrane in mammals. "The clathrin pit is almost like a hold box," says Christiansen. By contrast, in reptilian cells, bacteria appear to pass through the clathrin pits. The most likely explanation, according to the research team, is that certain cold shock proteins or cold-induced heat shock proteins operate on the clathrin pit in reptilian cells so that the latter are effective at low temperatures. The researchers have found that some of the cold shock proteins produced by reptilian cells are different from those produced by mammalian cells. They were also the first to find clathrin and cold shock proteins in reptiles.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Research Team:

James Johnson
Department of Microbiology
Des Moines University--Osteopathic Medical Center
james.johnson@dsmu.edu

Mark Ackermann
Department of Veterinary Pathology
Iowa State University
mackerma@iastate.edu
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Results:

1. At low temperatures, mammalian cells can carry bacteria just inside the cell membrane, but,
unlike reptilian cells, they cannot completely internalize and process the bacteria.

2. No physical actin barrier was found in either mammalian or reptilian cells that would interfere
with the process of internalization after the bacteria are consumed.

3. Reptilian cells and mammalian cells have negligible ability to synthesize protein at low
temperatures.

4. Different groups of cold-induced proteins were identified for reptilian cells than for mammalian
cells.

5. At all temperatures with MMs, clathrin was present on the membrane with bacteria, and
bacteria were present in the cytoplasm, free of clathrin. This suggests that in reptilian cells as in
mammalian cells, the bacteria may pass through clathrin pits in the membranes and be released
into the cytoplasm.

6. The heat shock protein 70 group was present in the cells at all temperatures tested, and this is
the first report of this protein in a reptile in response to cold.