The work of Peter Armstrong

This section describes the current work of Dr. Peter Armstrong of MBL and the University of California-Davis who is continuing to reveal interesting properties in the blood of horseshoe crabs, this time in the blood serum itself. See also "Standing the Test of Time" from LabNotes 4:3
Limulus continues to reveal new secrets. MBL summer researcher Peter B. Armstrong of the University of California-Davis has been investigating a recent discovery. When endotoxin is introduced to the blood of Limulus, it secretes a proteinous substance over it's outer shell, or carapace which was discovered to cause lysis (disruption) of blood cells and a general antibiological activity. Antibiotic agents in general are of interest to science and the isolation and understanding of these are still underway. It is theorized that Limulus secretes these proteins to inhibit colonization of it's carapace by the myriad of settling plankton looking for a empty place to set up home. In fact, most healthy Limulus from clean waters are surprisingly free of the barnacles, algae and other organisms usually found on rocks and pilings in the shallows.*

Armstrong's research is focusing now on the hemolymph itself, the part left over after the cells are remove and the cytolytic properties this blood plasma possesses. The protein limulin for example, has been identified as having potent cell-killing abilities. These properties have been exhibited in nanomolar (billionths of a mole) solutions of physiological salines.

Many of these proteins identified in Limulus blood are also found in many other taxa including humans. As in many cases, humans possess more complicated systems of overlapping biochemical processes and sorting out the roles of individual proteins is hampered by the numbers of "players." Limulus is viewed a simpler model systemm where biochemical mechanisms can be more easily isolated and observed.

Limulus CRP molecule
A group of proteins known as petraxins are believed to have a relationship with bacterial infections in humans. It has been observed that in healthy people, the level of one of them, CRP, is relatively low whereas in the presence of infection this protein increases in concentration. So correlated is the concentration of this protein with infection that physicians uses it's relative concentration and the rate of increase or decrease as a marker to monitor the course of the infection. Functionally it is believed that this protein is used to inhibit the spread of bacteria by removing the protolytic proteases that pathogens exude. It is these proteases that allow them to take grow and divide, hence spreading infection.

This same protein is also found in the blood serum of Limulus and studying it there may also shed light on how the immune system of a simpler animal functions as well. It also may provide the burgeoning industries of crustacean aquaculture (shrimp, crab and lobster) with knowledge and even tools in the battle with infections in their stocks.

It is this sort of basic research, exploring and following ideas, making mistakes, stumbling upon surprises, that sometimes leads to novel discoveries. Science isn't a perfect process and serendipity, being the right person in the right place at the right time asking the right questions, plays a significant role in discovery. In the case of Limulus, it has made a case for preservation. This ancient animal is having a hard time on our coasts. Where there once was a bounty and now there are fishing pressures, there is also a voice for preservation. Science has added new reasons for maintaining and preserving not just Limulus but healthy and diverse environments for there is still much to learn and discover.

References used in this section

1. -Segukuchi, Koichi, 1988, "Hemocytes and Coagulogen, A coagulation factor," Biology of Horseshoe Crabs, p.334

2. -Segukuchi, Koichi, 1988, "Hemocytes and Coagulogen, A coagulation factor," Biology of Horseshoe Crabs , p.334

3. -Segukuchi, Koichi, 1988, "Hemocytes and Coagulogen, A coagulation factor," Biology of Horseshoe Crabs , p.338

4. Mürer, E.H., Levin. J. and Holm, R., 1975. Isolation and studies of the granules of the ameobocytes of Limulus polyphemus, the horseshoe crab. J. Cell Physiol., 86: 533-542

5. Armstrong, P.B. 1979, Motility of the Limulus Amebocyte, Biomedical Applications of the Horseshoe Cran (Limulidae), 73-92.

Quigley, J.P., Corcoran, G., Armstrong, P.B., A Hemolytic Activity Secreted by the Endotoxin-Challenged Horseshoe Crab: A Novel Immune System Operating at the Surface of the Carapace. , Biological Bulletin, 193: 273 (October 1997)

6. Milne, Edwards, H., Historie naturelle des Crustacea., Paris, 1834-40

7. Milne, Edwards, H., L'Anatomie des Limules, 1873

8. Sargent, William., The Year of the Crab., W.W. Norton & Company 1987