A case for natural immunity.

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Web address:

http://www.sciencedaily.com/releases/2006/06/060630083627.htm [input]

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Source: American Thoracic Society

Posted: June 30, 2006

Developing Natural Immunity To Asthma Caused By Research Rats Laboratory

workers who frequently handle research rats that commonly cause asthma symptoms

have fewer allergic reactions to the rats than individuals with less exposure,

according to a study at six pharmaceutical sites in Great Britain.

The findings appear in the first issue for July 2006 of the American Journal

of Respiratory and Critical Care Medicine, published by the American Thoracic

Society.

Meinir , Ph.D., of the Department of Occupational and Environmental

Medicine at Imperial College in London, and five associates analyzed the

background information and blood tests of 689 pharmaceutical employees who had

been exposed to lab rats in varying degrees.

The investigators wanted to learn more about the complex relationship between

allergen exposure from the animals and the induction of human asthma. They noted

that occupational asthma caused by an allergy to a laboratory animal can provide

a useful model of allergic reaction from which exposure can be readily

characterized and measured.

" We recorded the dates of their first and most recent handling of rats and

estimated the duration of contact with rat proteins, " said Dr. . " Employees

were classified according to the job they had that incurred the highest exposure

to rats, with office and maintenance workers showing low exposure, scientists

medium exposure, and animal technicians or cage cleaners high exposure. "

There was close agreement between the exposure category associated with the

job title and the maximum number of rats handled in one day.

" Approximately 38 percent had handled more than 50 rats per day, whereas 17

percent had never handled any, " said Dr. . " There were equal proportions,

23 and 22 percent, who had handled either from 1 to 10 or 11 to 50 rats. For 464

employees or 68 percent, their highest exposure to rat proteins came during

their work as a scientist. "

For the first time, the authors found a two-fold reduction in the risk of

developing work-related chest symptoms in those who produced both rat-specific

IgG4 and IgE antibodies, as compared with those producing IgE alone.

Immunoglobulin G (IgG) is one of five classes of immunoglobulins, which

constitute the human body's main antibody defense against most bacterial

invasions. Immunoglobulins also trigger antibodies against other antigens.

IgG is present primarily in human skin and mucus membranes. It functions in

response to environmental challenges and plays a role in allergic reactions to

those challenges.

" Laboratory animal workers may, at very high exposure, be experiencing a

natural form of immunotherapy, " said Dr. . " Interestingly, this does not

seem to be the case for other groups at risk of occupational asthma such as

bakers and detergent manufacturers. We propose that the differences arise

because laboratory animal workers experience exposure not only through

inhalation but also through an intradermal route after bites and scratches. "

In an editorial on the research in the same issue of the journal, Karin A.

Pacheco, M.D., M.S.P.H., of the National Jewish Medical and Research Center in

Denver, wrote: the authors " speculate that the protective effect against

symptomatic disease offered by a high IgG4-IgE ratio reflects a form of natural

immunotherapy. "

" One of the strengths of the present manuscript is the categorization of

exposure by the highest level, ever, of work with rats. This approach suggests

that peak exposures are more important for the development of immune responses

to laboratory animals than average exposures and acknowledges that exposure

responsible for sensitization may have occurred in the past. "

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