cats good for allergy -followup references

[David Honig]

In a thread "Re: When the FBI Guys Come Knocking..." I claimed
(from memory) that cats can decrease allergies.  I was unable
to find the _Science_ ref but I
found a few refs to the original research reported in 
The Lancet 357:752-56 (2001).   Reproduced below.  I don't
make this stuff up.


http://www.niaid.nih.gov/newsroom/focuson/asthma01/research.htm#cats

Contrary to popular belief, high levels of cat allergen in the home can 
sometimes decrease the risk of a child developing
asthma, says grantee Thomas A. 
Platts-Mills, M.D., Ph.D., of the University of
Virginia. Apparently, the presence of a cat can 
alter the immune system in a manner similar to
allergy shots, he reports.

For other allergens that trigger asthma, such as the
dust mite and cockroach, the higher the 
exposure level, the more likely it is that a child
will produce "allergic" antibodies, called 
immunoglobulin-E or Ig-E antibodies, against them.
This high exposure increases the child's risk 
of becoming allergic and developing asthma.

But with cats, high exposure actually can confer
protection -- at least in some children, Dr. 
Platts-Mills says. He and colleagues measured the
levels of allergic antibodies to cat allergen in 
226 children, aged 12 to 14 years, and tested the
children for asthma. They also measured the 
amount of cat allergen in the children's homes and
discovered that low-to-moderate amounts of 
cat allergen seemed to trigger allergy, but high
amounts -- greater than 20 micrograms per gram 
of house dust -- reduced both IgE antibodies and the
likelihood of asthma.

                      "This result alters the advice we give patients,"
says Dr. Platts-Mills. "I would not recommend 
                      that all parents get rid of their cat because they
are concerned their child might develop asthma. 
                      High exposure to cat allergen appears to be
protective for some children and a risk factor for 
                      others. If the child is wheezing and has a positive
skin test to cat allergen, then you should get rid 
                      of your cat."

                      The high levels of cat allergen prompted the
children's immune systems to make mostly a 
                      particular subtype of immunoglobulin G (IgG), called
IgG4 antibody, rather than IgE, Dr. 
                      Platts-Mills explains. Allergy shots are believed to
produce a similar effect. "This research sheds 
                      more light on the relationship between allergen
exposure and asthma," he says. "When we 
                      further understand this process, it might lead to new
treatments for asthma." 

                      Reference: T Platts-Mills et al. Sensitisation,
asthma, and a modified Th2 response in children 
                      exposed to cat allergen: a populations-based
cross-sectional study. The Lancet 357:752-56 
                      (2001). 



Sensitisation, asthma, and a modified Th2 response in children exposed to cat
                       allergen: a population-based cross-sectional study.

                       Platts-Mills T, Vaughan J, Squillace S, Woodfolk J,
Sporik R.

                       University of Virginia Asthma and Allergic Diseases
Center, University of Virginia Department
                       of Medicine, Charlottesville, USA. tap2z at virginia.edu

                       BACKGROUND: Although asthma is strongly associated
with immediate hypersensitivity to
                       indoor allergens, several studies have suggested
that a cat in the house can decrease the risk of
                       asthma. We investigated the immune response to cat
and mite allergens, and asthma among
                       children with a wide range of allergen exposure.
METHODS: We did a population-based
                       cross-sectional study of children (aged 12-14
years), some of whom had symptoms of asthma
                       and bronchial hyper-reactivity. Antibodies to mite
(Der f 1) and cat (Fel d 1) allergens
                       measured by isotype (IgG and IgG4) specific
radioimmunoprecipitation assays were compared
                       with sensitisation and allergen concentrations in
house dust. FINDINGS: 226 children were
                       recruited, 47 of whom had symptoms of asthma and
bronchial hyper-reactivity. Increasing
                       exposure to mite was associated with increased
prevalence of sensitisation and IgG antibody to
                       Der f 1. By contrast, the highest exposure to cat
was associated with decreased sensitisation,
                       but a higher prevalence of IgG antibody to Fel d 1.
Thus, among children with high exposure,
                       the odds of sensitisation to mite rather than cat
was 4.0 (99% CI 1.49-10.00). Furthermore, 31
                       of 76 children with 23 microg Fel d 1 at home, who
were not sensitised to cat allergen had
                       >125 units of IgG antibody to Fel d 1. Antibodies to
Fel d 1 of the IgG4 isotype were strongly
                       correlated with IgG antibody in both allergic and
non-allergic children (r=0.84 and r=0.66,
                       respectively). Sensitisation to mite or cat
allergens was the strongest independent risk factor for
                       asthma (p<0.001). INTERPRETATION: Exposure to cat
allergen can produce an IgG and
                       IgG4 antibody response without sensitisation or risk
of asthma. This modified T-helper-2 cell
                       response should be regarded as a form of tolerance
and may be the correct objective of
                       immunotherapy. The results may also explain the
observation that animals in the house can
                       decrease the risk of asthma.

                       PMID: 11253969 [PubMed - indexed for MEDLINE]