ROANOKE TIMES
Copyright (c) 1997, Roanoke Times
DATE: Friday, January 3, 1997 TAG: 9701030080
SECTION: NATIONAL/INTERNATIONAL PAGE: A-3 EDITION: METRO
DATELINE: THE WASHINGTON POST
THE HYPOTHESIS is that vaccinations have weakened the effect of one of the immune system's two mechanisms.
Asthma rates are skyrocketing in the United States and other Western nations not because of increased air pollution or other environmental toxins, as many scientists have theorized, but because people are getting fewer serious respiratory diseases in childhood, a provocative new study suggests.
The study, in today's issue of the journal Science, suggests that diseases such as tuberculosis and whooping cough may permanently alter a child's immune system in a way that confers lifetime protection against asthma. If true, then the public-health victories of the past few decades that have largely eliminated those diseases in developed nations may be making people more susceptible to asthma or other allergies.
On a positive note, researchers said, the findings suggest asthma might be prevented by giving children a vaccine that mimics a serious lung infection.
``Immunization with harmless bacteria, related to tuberculosis, might be helpful in preventing and treating allergy,'' said lead researcher Julian M. Hopkin of Churchill Hospital in Oxford, England.
Experts called the findings controversial, and even the study's authors conceded their conclusion is based both on science and speculation. But several experts said the hypothesis made sense and deserved serious attention, given the scope of the global asthma epidemic and the lack of understanding about its cause.
More than 14 million Americans have asthma - an allergic overreaction to airborne particulates such as pollen or dust in which a flood of antibodies causes lung inflammation, airway restriction and a life-threatening shortness of breath. That's about twice as many as had the disease in 1982.
Asthma incidence and death rates have increased similarly in Europe, Japan and other developed countries, leading some researchers to blame air pollution or other aspects of modern living. But recent findings of low asthma rates in several cities with extremely dirty air have partially exonerated environmental toxins.
The new research focused on 867 schoolchildren in Japan who, like most Japanese, received so-called BCG vaccines at birth and at age 6 and 12. That vaccine is made from a kind of bacteria closely related to the one that causes tuberculosis, and is popular in some countries to help prevent that disease. It is not commonly used in the United States, in part because it inexplicably fails to stimulate the immune system in many recipients.
Hopkin and his co-workers in Wakayama, Japan, tested fully vaccinated 12- and 13-year-olds to see whether they had developed the intended immune response against tuberculosis. They also checked for a history of asthma or related allergies, and performed immune-system tests.
Children who mounted the strongest immune responses against BCG had about one-third the incidence of asthma compared to children with weak or no immune response. The researchers conclude that exposure to tuberculosis or related microbes may help protect against asthma, and they offer an explanation of how.
The immune system uses two main arsenals to protect the body. One system centers on antibodies, which when over-produced in the lungs cause asthma. The other system, called cell-mediated immunity, centers on white blood cells called macrophages, and is the main response to respiratory infections and BCG vaccinations.
Generally speaking, when one arm of the system is operating, the other backs off. The researchers propose that in the absence of severe childhood lung infections, youngsters never develop the strong cell-mediated response that might permanently temper the antibody arm. (Unlike the BCG vaccine, vaccines against whooping cough and other childhood diseases in this country stimulate antibodies but not cell-mediated immunity.) Without that early cell-mediated response, they propose, the antibody-generating arm of the immune system is left unbridled and poised to overreact to particles such as dust or pollen.
LENGTH: Medium: 74 linesby CNB