7 May 2002 16:00 GMT

by Bill O'Neill, BioMedNet News

Lack of exposure to common infections during early childhood delays the maturing of a child's immune system and, in rare cases, may be responsible for increasing susceptibility to acute lymphoblastic leukemia (ALL), the most common form of childhood leukemia, today reveals a team of US researchers.

Children with underdeveloped immune systems respond abnormally when eventually exposed to infection by producing defective leukocytes, which fail to provide immunological protection but accumulate and lead to ALL, they suggest.

Attendance at nurseries, vaccinations, and exposure to siblings and friends are among the many ways of stimulating the development of the immune system, according to Patricia Buffler, professor of epidemiology at the University of California, Berkeley and principal investigator of the Northern California Childhood Leukemia Study, which produced the findings.

"Our study contributes to the idea that isolation from common infections can increase the risk of childhood leukemia," Buffler noted. "While our results strongly support the importance of the timing of infections in the development of childhood leukemia, we are not able to distinguish whether a particular infection or a number of common infections are involved."

The current results are only the first phase of an ongoing study, says Xiaomei Ma, assistant research assistant at Berkeley and the study's author. "We anticipate that later studies will confirm the association between delayed exposure to infection and childhood leukemia and eventually lead to effective prevention strategies."

The team used nursery attendance as an indicator of a child's exposure to common infections.

They analyzed 140 children, aged from 1 to 14, who were diagnosed with ALL between 1995 and 1999, and they compared this group with another group randomly selected from the California birth registry. The children's guardians provided detailed data on nursery attendance.

Statistical analyses showed that factors such as starting nursery at a younger age, attending for a longer duration, and having contact with a high number of children all contributed to a reduced risk of ALL.

The findings, published today in British Journal of Cancer, are welcomed by Paul Nurse, interim chief executive of Cancer Research UK. "This research adds to the increasing evidence that infections play a role in some cancers, the nature of which is still unknown," he noted.

Cancer Research UK is currently funding the UK National Childhood Cancer Study, which is looking at the link between infections and leukemia in more than 1,000 children. "Further investigation into exposure to infection with larger numbers of children should help us to identify the role of the immune system in childhood leukemia and may lead to new ways to prevent the disease," Nurse added.

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