L-H

.FA

GE

W W W. S C I E N C E N E W S. O R G S E P T E M B E R 6 , 2 0 0 3 V O L . 1 6 4 1 4 7

Double ShotAnthrax vaccine gets makeover

Anthrax, a scourge once confined to farm-ers and wool handlers, has become a mem-ber of the rogues’ gallery of biologicalweapons. Although there’s a vaccine againstanthrax, it’s been the target of such strongcriticism that a government-funded panellast year recommended that researchersfind an alternative.

Scientists now report that in mice, a dual-purpose experimental vaccine appears tospur the immune system to disableanthrax’s lethal toxin at the same time itkills the bacterium. The current vaccine tar-gets only the toxin.

Meanwhile, another group presents newfindings about how anthrax toxin kills.

Researchers at Harvard Medical Schoolin Boston gave mice three injections ofeither the vaccine or an inert substance over4 weeks. Two weeks after the last shot, theanimals received an injection of anthraxtoxin. All vaccinated mice survived, havingformed antibodies that recognized and dis-abled the toxin. The other mice all diedwithin a day of receiving the toxin.

In another part of the experiment, theresearchers drew blood from vaccinatedmice and exposed it to the bacteriumBacillus licheniformis as a stand-in for themore dangerous Bacillus anthracis, whichcauses anthrax. The vaccinated mice madeantibodies that surrounded and killed B.licheniformis, suggesting that the new vac-cine would do the same to B. anthracis,says study coauthor Julia Y. Wang. Thefindings will appear in an upcoming issueof the Proceedings of the National Acad-emy of Sciences.

“It’s a double whammy,” says Vincent A.Fischetti of Rockefeller University in NewYork. The new vaccine will include mate-rial from the capsule that normally shieldsB. anthracis from the immune system. Tomake the two-part experimental vaccine,Wang and her colleagues chemicallyattached B. licheniformis capsule materialto a portion of the B. anthracis toxin. The

combination made the bacterium “visible”to the mouse immune system, Wang says.

This same strategy works in a pneumo-nia vaccine already in use, Fischetti says.

The current anthrax vaccine requiressix shots over 18 months. The panel ofthe Institute of Medicine (IOM) in Wash-ington, D.C., last year cited this regimenas a major drawback. The new dual-action vaccine could require half as manyshots, Wang says.

However, the new vaccine would containthe same antitoxin ingredient that consti-tutes the existing vaccine. So it’s unclearwhether it would avoid the fatigue, mem-ory loss, malaise, and other symptomsreported by some of the roughly 2 millionmilitary and other personnel who havereceived the current anthrax inoculations.

The IOM panel found no more adverseeffects with the existing vaccine than withseveral of those for other diseases.

Even as Wang and her colleagues striveto develop a better anthrax vaccine, otherscientists are still trying to decipher thedetails of how the microbe’s toxin kills.New findings indicate that the toxin causesharm distinctive from that of other bac-teria. It triggers “a unique kind of shock,”says Stephen H. Leppla of the NationalInstitute of Allergy and Infectious Dis-eases in Bethesda, Md.

Researchers have known that anthraxtoxin damages blood vessels, resulting ininternal bleeding and a buildup of fluid

around the lungs that impedes breathing.One school of thought holds that the toxinattacks immune cells called macrophagesand that this assault unleashes inflamma-tory proteins that damage the blood ves-sels. Leppla and his colleagues observedhundreds of mice reacting to anthrax toxin.In the September Journal of ClinicalInvestigation, the researchers report thattwo primary suspects among the inflam-matory proteins don’t seem to play a largerole in the disease.

However, the team found that the animals’tissues become starved of oxygen. Damagewas greatest to the liver, spleen, and bonemarrow, says Leppla. Liver damage canrelease chemicals that do wide-rangingharm. “I’d like to know the molecular eventscausing liver cells to die,” Leppla says. Thenew findings might spur research into thetoxin’s effect on liver cells, he adds. —N. SEPPA

Art on theRocksDating ancient paintingsin the caves of Borneo

The matchstick figures and images of handslining the Gua Saleh Cave in southeast Bor-neo were made at least 9,900 years ago, ateam of French archaeologists has deter-

SCIENCENEWSThis Week

HANDIWORK These two hand shapes are joined by a symbol-adorned path. The artist appliedpigment around a hand, then painted the lines.

FOBs 9-6 9/3/03 15:02 Page 147

NA

SA,J

.BEL

L,M

.WO

LFF

S C I E N C E N E W S

mined. That date suggests that peopleinhabited the Asian island, the third largestin the world, some 4,000 to 5,000 years ear-lier than scientists had previously believed.

“It’s difficult to know exactly how old thepaintings are,” says Jean-Michel Chazine ofthe National Center for Scientific Researchin Marseille, France. He and his team estab-lished the artworks’ minimum age by esti-mating when a mineral coating on thepaintings had begun to form.

Paul Tacon of the Australian Museum inSydney comments that the study is“extremely important, [providing] the firstsignificantly old and reliable date for rockart of the region.” He’s not surprised by theearly date for the artwork, however. It’s

“consistent with recent research by a rangeof scholars in nearby Timor and other partsof southeast Asia,” he says.

Usually, archaeologists date rock art byevaluating the carbon content of organicpigments. However, the Gua Saleh Caveartists used pigments containing no car-bon; they’re made of pure hematite, aniron-ore mineral. So, Chazine and his col-leagues used carbon dating on the calcitecoating the paintings. Calcite, or calciumcarbonate, is the main constituent of lime-stone and of cave formations such as sta-lagmites and stalactites.

Chazine and his team dated the calcitethat had deposited over two hand shapesapplied to the cave walls by the ancientartists. The researchers used a methodknown as uranium-thorium dating tocross-check the carbon-dating estimateof the calcite layer’s age. Both methodsrely on measuring the extent of radioac-tive decay of elements normally inter-spersed within the calcite.

In their study, published in the SeptemberQuaternary Research, the researchers usedates from both methods to estimate thatthe calcite veil is about 9,900 years old.Therefore, the paintings must be at least thatold. Still unknown is how much time passedbetween the creation of the paintings andthe formation of the calcite covering.

Because the Gua Saleh Cave and otherslike it are in limestone outcrops—some ashigh as 1,000 meters above Borneo’sforests—the island’s prehistoric inhabitantsprobably didn’t live in the caves, but onlyvisited them for important rites, Chazinesays. Making images of hands was proba-bly part of rituals such as healing cere-monies, he says. —S. MCDONAGH

Hubble Highlights a RiddleWhat’s the source of quick-return comets?

New observations from the Hubble SpaceTelescope are demonstrating that scientistsdon’t know where a major class of cometscomes from.

Until recently, most planetary scientistshad assumed that comets that take less than20 years to orbit the sun originally residedin the Kuiper belt, a doughnut of icy mate-rial left over from the formation of the plan-ets 4.5 billion years ago. The belt lies justbeyond the orbits of Neptune and Pluto.But new observations suggest that to serveas a storehouse for comets, the Kuiper beltis too thinly populated with suitable objects.

Last winter, Hubble’s Advanced Camera

for Surveys stared for 200 hours at a tinyregion of sky, just 10 percent the size of thefull moon as seen from Earth. Gary M. Bern-stein of the University of Pennsylvania inPhiladelphia used a bank of 10 computersfor 6 months to search the resulting imagesfor faint objects moving in the Kuiper belt.

The study revealed three such objects,the brightest of which was subsequentlyrecorded by the Keck 1 Telescope atopMauna Kea in Hawaii. Ranging in diame-ter from 25 to 45 kilometers, the bodies arethe smallest objects ever detected at thefringes of the solar system and are one-bil-lionth as bright as the dimmest celestialobjects visible to the naked eye. Theoreti-cal predictions about the origin of short-period comets, which traverse the innersolar system, had led Bernstein and his col-leagues to expect to find about 85 of thesebodies in the Hubble images. At press time,Bernstein was scheduled to report the find-ings Sept. 6 at a meeting of the AmericanAstronomical Society in Monterey, Calif.

For the Kuiper belt to be the supplier of theshort-period comets, it ought to contain hun-dreds to thousands of times as many bodiesas the images suggest, Bernstein’s team cal-culates. A few years ago, Hal F. Levison of theSouthwest Research Institute in Boulder,Colo., and a colleague suggested an alterna-tive source for short-period comets. Theyproposed the group of objects known as thescattered disk, which extends from the outeredge of the classical Kuiper belt.

The new observations suggest that eventhis population of fringe objects might notbe sufficiently massive to spawn the short-period comets, says Bernstein.

His team has proposed an explanationfor the dearth of appropriate-size Kuiperbelt objects: Many of the larger bodies theremay have been shattered into bits by colli-sions. In fact, other researchers have sug-gested that the outward migration of Nep-tune or some other planet early in thehistory of the solar system triggered colli-sions within the Kuiper belt.

The new work is “spectacular,” says Lev-ison, because it provides the first data onthe size of objects in the Kuiper belt. Thestudy not only highlights the uncertaintyabout the origin of comets but also pro-vides important clues about the formationand evolution of the outer solar system,he says. —R. COWEN

Skin ChemistryPoison frogs upgradetoxins from prey

For the first time, scientists have founda poisonous frog that takes up a toxin fromits prey and then tweaks the chemical tomake it a more deadly weapon.

1 4 8 S E P T E M B E R 6 , 2 0 0 3 V O L . 1 6 4

SCIENCENEWSThis Week

Cozying up to MarsThe Hubble Space Telescope took thiscolor-composite portrait of Mars onAug. 26, just 11 hours before the RedPlanet passed within 56 million kilo-meters of Earth, its closest approachin 59,619 years. The image, whichshows Mars’ south polar ice cap(bottom) and the huge Hellas basinimpact crater (circular feature belowand right of center), is the sharpestglobal picture of the Red Planet evertaken from Earth‘s vicinity. Mars andEarth approach each other unusuallyclosely about every 17 years, but thetwo orbs won‘t reach last week’sproximity again until 2287. ThroughSeptember, Mars will rise in thesoutheast at sunset and set in thesouthwest at dawn. Luminous in the night sky, the planet resembles a butterscotch-colored star thatdoesn’t twinkle. —R. COWEN

FOBs 9-6 9/3/03 15:02 Page 148