Llama Blood Against Biological Terrorist Attacks

Llama antibodies have special properties

By on December 6th, 2006 12:08 GMT
Scientists have found that llama blood could quickly detect biological terrorist attacks and all sorts of maladies in the surrounding environment due to an unusual molecular structure of their antibodies. Llama blood could be made an inexpensive and diverse biosensor.

Immune cells in the blood and lymph use antibodies to identify attacks or to directly bind to and neutralize germs. Currently, antibodies are used in medicines against cancers and other diseases or in sensors to warn of dangerous microbes and chemicals. Common mammalian antibodies are Y-shaped, made up of two different protein chains: one heavy and one light. The heavy chain is about two and a half times larger than the light one.

Each short-end of the antibody bears the complementarity determining regions (or CDRs), where they bind antigens, or foreign substances. The use of antibodies in the emerging field of biosensors has stumbled with their instability at temperatures of about 60-70 degrees Celsius. "That's the Achilles' heel of these antibodies--when you start heating them up, those domains come apart and they catastrophically aggregate and they refold and they can't reassemble," says Andrew Hayhurst, a virologist and immunologist at the Southwest Foundation for Biomedical Research.

But CDRs in camels (llamas are related to the camels) and sharks are unusually small, just 10 % the size of common human antibodies. Llama, camel and shark antibodies miss the lighter protein chain found on the antibodies of other species. This relative simplicity makes them more durable, capable of withstanding temperatures of almost 90 degrees C. "If they do unfold, they can actually completely refold on cooling and they can cycle over and over again," Hayhurst explains. "For field use, where you don't have very much refrigeration--in the developing world, for example--you could have an infinitely stable diagnostic assay for infectious disease."

"We're interested in the development of biosensors for biothreats in the field, and hopefully these antibodies will help lead to more rugged antibodies that have longer shelf lives and not require refrigeration," Goldman said.

This technology could employ antibodies against emerging threats within hours. The research team wants to improve the binding ability of the antibodies. When the team tried to clone antibodies from three llamas, the resulting antibodies did not bind well to several biothreats they desired to test, like ricin, cholera toxin and vaccinia (a surrogate of smallpox virus).

Within the llama, these antibodies would adapt to a new antigen through hypermutation, but the antibodies must be created "in vitro". The team manipulated the CDRs genes, randomly mutating them to generate a varied library of binding sites for their biosensor. These semisynthetic antibodies have "far more diversity, so there's far more chance of actually pulling out a binder to any target you want." said Hayhurst.

Once they had their better-binding antibodies, the group tested their thermal stability by exposing them to a temperature of 95 degrees C. The semisynthetic variety kept at least some of their functionality for as long as 80 minutes, at 95 degrees C, while the natural ones typically broke down completely within five minutes. The genetically manipulated antibodies could withstand field use in hot, dry areas. "We're looking at diagnostic assays for Ebola and Marburg viruses that we can actually take out into the field in Africa--dreadfully resource-poor environments, incredibly hot and where we need diagnostic assays," Hayhurst says.

Clement Furlong, a researcher in medical and genomic sciences at the University of Washington observed that the "huge advantage" of these antibodies "is that you can make them by fermentation in microbial systems and make a lot of antibodies inexpensively."