ENGLAND JOURNAL OF MEDICINE VUM). Blood tests showed that immunoglobu-

lin E, an antibody abundant in people with asthma, was plentiful in 35 percent of the less exposed children but in only 27 per- cent of the other group. The researchers also did skin tests to gauge sensitivity to alternaria, an allergy-causing mold in the Tucson area. They found that 25 percent of the children who had been less ex- posed to other kids reacted to it, com- pared with 17 percent of the children who had been in early day care or had multiple older siblings.

By age 2, the children with greater ex- posure to kids as infants had experienced more wheezing episodes than the others. By age 8, however, this group reported less wheezing than the other children. In the preschool years, wheezing is typical- ly caused by infections, but in school-age children, it more often results from aller- gies or asthma, Wright notes.

Several previous studies showed that babies in day care contract more infec- tions on average than stay-at-home chil- dren do. Another study found that in- fants placed in day care had fewer

allergies later than did children who en- tered day care at an older age. Scientists consider asthma a subset of allergy.

The hygiene hypothesis holds that ex- posure to microbes provides an infant’s immune system with clear signals for proper development, Wright says. Several recent studies have bolstered that con- tention, suggesting that parents in indus- trialized societies, where asthma rates have soared, permit children too little contact with germs.

“We didn’t evolve in some sort of ster- ile capsule. We evolved in a hostile envi- ronment,” says Julian M. Hopkin of the University of Wales in Swansea. “This [study] strengthens the idea that . . . mi- crobial exposure may limit asthma.”

“For those of us who share the furtive guilt of having left marginally ill toddlers at day care, these findings also offer a sense of relief,” says Sandra C. Christiansen of the Scripps Research Institute in La Jolla, Calif., in the same NEJM issue. “We were perhaps only doing our part to re- store the [immune-system] balance and to stem the rising tide of asthma and al- lergic disease.” -N. Seppa

Apollo attire needs care

Tales from the crypts: Cells battle germs Consider them the guardian angels of

your small intestine. Long known as Paneth cells, these sen-

tries inhabit tiny pits in the intestine called crypts. Scientists now offer the best evidence yet that these cells defend other cells in the crypts by discharging bacteria-killing bursts of enzymes and other molecules.

Protecting the crypt’s so-called stem cells, which replenish the lining of the small intestine, is vital. With a surface area about the size of a football field, the lining is continually damaged by diges- tive enzymes and bile. It must therefore turn over rapidly, every few days in a person. It’s up to the stem cells, which dwell just above the Paneth cells, to spawn progeny that migrate onto the tips of fingerlike villi that line the intes- tine and absorb nutrients.

For years, scientists have amassed a case that Paneth cells safeguard stem cells. They initially found that Paneth cells contain stores of lysozyme, an en- zyme that breaks down bacterial cell walls. More recently, they documented similar accumulations of defensins, small proteins with antimicrobial powers. Still, it remained unclear whether Paneth cells use these as weapons to destroy germs.

Andre J. Ouellette of the University of California, Irvine and his colleagues had hoped to study Paneth cells by growing them in petri dishes, but the cells failed to thrive. The investigators instead used intestinal tissue from mice and exposed the tissue’s intact crypts to various mi- crobes and microbial molecules. Bacte- ria, including the food-poisoning culprits

AUGUST 26,2000

Escherichia coli and Salmonella typhimuri- um, trigger the Paneth cells to secrete large amounts of defensins and other molecules, the researchers report in the August NATURE IMMUNOLOGY.

The work of Ouellette and his col- leagues “is a successful culmination of ef- forts to understand Paneth cell function,” comments Tomas Ganz of the University of California, Los Angeles in the same journal. “They determine that Paneth cells are the sentinels of crypts: they re- act to bacteria by releasing defensins in more than sufficient quantity to kill.”

While Paneth cells appear to protect crypts from bacteria, biologists still must investigate whether the cells’ sterilizing power extends into the general cavity of the small intestine. Full of nutrients that an animal is trying to absorb, the small intes- tine would seem to offer a pleasant home to bacteria and other microorganisms. Yet compared with the colon, the small intes- tine harbors significantly fewer microbes.

Paneth cells may be the reason, sug- gests Charles Bevins of the Cleveland Clinic Foundation. He notes that biolo- gists are also investigating whether prob- lems with Paneth cells lead to inflamma- tory diseases within the small intestine.

Ouellette’s team is now trying to identi- fy the bacteriadetecting surface mole- cules on Paneth cells. The researchers will also examine why their initial experi- ments found that Paneth cells don’t react to fungi or other nonbacterial microbes.

“We’ve just started to look at the re- sponses of these cells,” notes Donald P. Satchell, one of the study’s authors.

-1 Travis

SCIENCE NEWS, VOL. 158

Wearing out already? The pressure suit worn by David R. Scott in 1971.

Spacesuits were built to withstand the harsh enyironment of space. Sur- prisingly, their materials aren’t hold- ing up all that well here on Earth. Re- . searchers from the National Air and Space Museum’s Space History Divi- sion have started an 18-month proj- ect to analyze Apollo-era spacesuits, including the pressure suit worn by Apollo 15 mission commander David R Scott in 1971.

To assess the sometimes hidden degradation in each suit, scientists are performing CAT scans, which let them see inside the more than 20 lay- ers of synthetic polymers and natural rubber. They’re also inspecting the suits visually, testing their materials’ acidity, measuring fading and stain- ing, and interviewing the original spacesuit designers. By August 2001, the team will have new guidelines for storing and handling the suits, which represent some of the museum’s most frequently loaned artifacts.

Lisa Young of the National Air and Space Museum notes that museums contain objects that are 3,000 years old and seem to be holding up. “Peo- ple didn’t really consider that the spacesuits would be deteriorating so quickly,” she says. 4 Corman

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