Immune system targets asthma-linked fungus for destruction

Washington, Sep 3 : Our immune system is capable of killing a fungus linked to airway inflammation, chronic rhinosinusitis and bronchial asthma, according to a new study.

Researchers at Mayo Clinic and the Virginia Bioinformatics Institute (VBI) have revealed that eosinophils, a particular type of white blood cell (WBC), exert a strong immune response against the environmental fungus Alternaria alternata.

Eosinophils typically combats parasitic invaders of the human body larger than bacteria or viruses, such as flukes or parasitic worms (collectively known as helminths).

Evidence from different experimental approaches suggests that asthma and chronic sinusitis can arise when the body perceives that it has encountered a disease-causing organism.

Environmental fungi such as Alternaria do not typically cause invasive infections like parasites but for some reason, in certain people, the body responds as if it is being attacked and chronic inflammation can result from the ensuing cascade of immune-related events.

Principal Investigator Hirohito Kita of Mayo Clinic, observed "our results strongly demonstrate that eosinophils have the capacity to recognise and exert immunological responses to certain fungi such as Alternaria."

"We have shown that CD11b receptors on the surface of eosinophils recognize and adhere to beta-glucan, a major cell wall component of the fungus. This in turn sets in motion the release of toxic granule proteins by the white blood cells, leading to extensive damage and ultimate destruction of the fungus," he said.

To the best of our knowledge, this is the first time that live eosinophils and not just the intracellular components have been shown to target and destroy a fungus," Kita added.

The researchers used fluorescence microscopy to determine the outcome of the interaction between eosinophils and A. alternata. The contact of fungus with eosinophils resulted in bright red fluorescence due to the damaged fungal cell wall and subsequent death of Alternaria.

Immunohistochemistry confirmed the release of toxic granular proteins by eosinophils due to contact with the fungus.

Hirohito Kita added: "We have taken an important step in showing that the innate immune system of eosinophils is capable of targeting an asthma-associated fungus for destruction.

These findings were published recently in the Journal of Immunology.