“This study is the first to show a possible immunologic
basis for chronic sinusitis, an important starting point to better
understand the etiology of the illness,” says Marshall Plaut,
M.D., chief of NIAID’s allergic mechanisms section. Despite
the enormous health impact of chronic sinusitis — nearly
30 million people were diagnosed with sinusitis in 2002, according
to U.S. Centers for Disease Control and Prevention, and direct
costs of the illness exceed $5.6 billion per year — the condition
is very poorly understood, he says.
The researchers, led by Hirohito Kita, M.D., of the Mayo Clinic
in Rochester, MN, compared blood samples taken from 18 people diagnosed
with chronic sinusitis with blood samples from 15 healthy volunteers.
Nasal secretions from the two groups were also examined for the
presence of fungal proteins and inflammation-causing immune system
Airborne microscopic fungi spores abound indoors and out. People
may inhale a million or more fungal spores each day, notes Dr.
Kita. The mere presence of such fungi in the airways, however,
is not enough to cause sinusitis because these spores can be found
in the upper respiratory tracts of both sinusitis sufferers and
non-sufferers. Indeed, in this study, levels of fungal proteins
in nasal secretions were similar in both groups.
The Mayo Clinic scientists looked for evidence that people with
sinusitis respond abnormally to these harmless fungi. The investigators
exposed immune cells derived from the blood samples to extracts
of four common airborne fungi: Alternaria, Aspergillus, Penicillium
and Cladosporium. The cells of chronic sinusitis sufferers released
significant amounts of three immune-modulating chemicals, called
cytokines, specifically interferon-gamma, interleukin-5 (IL-5)
and IL-13. In contrast, cells from healthy volunteers released
very little interferon-gamma and no IL-5 or IL-13. The most dramatic
responses occurred after exposure to Alternaria.
Importantly, says Dr. Kita, the released cytokines
represent both major classes of cytokines — interferon-gamma
is in the Th1 group and IL-5 and IL-13 are in the Th2 class.
because scientists have thought that allergic reactions involve
only Th2 cytokines, Dr. Kita explains. (While chronic sinusitis
is not considered to be an allergic disease, people with the
condition also often have asthma and allergic rhinitis, giving
reason to suspect a link.) The current findings add to an evolving
understanding of allergic diseases that suggests symptoms may
stem from a combination of Th1 and Th2 cytokines.