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Australian and Dutch researchers have uncovered a remarkable evolutionary adaptation in birds that could hold vital clues for combating avian flu and respiratory infections in humans, including pneumonia and COVID-19.

The , published in Philosophical Transactions of the Royal Society B, investigates the molecular evolution of specific types of proteins (CL-10 and CL-11) in bird lungs, revealing the role they play in recognising and neutralising harmful microbes.

These ancient proteins appear to compensate for the evolutionary loss of the surfactant protein D (SP-D), a key immune component in humans and other mammals that helps protect the lungs from airborne pathogens.

According to pulmonary biology researcher, , the study sheds new light on how birds maintain lung protection despite their unique respiratory anatomy that does not allow their lungs to contract and expand.

“Unlike mammals, birds have a rigid lung structure with unidirectional air flow, which has evolved to support flight,” Prof Orgeig says.

“Our research shows that CL-10 and CL-11 have been highly conserved in birds, suggesting they play a crucial role in lung immunity, possibly compensating for the loss of SP-D.”

Birds are known reservoirs for several zoonotic infections (diseases that are transmitted between animals and humans), including avian flu and other airborne pathogens. Understanding their lung immunity could provide important insights into how these diseases spread, and how to prevent them.

The team conducted an extensive analysis using molecular and genetic techniques, confirming the presence of CL-10 and CL-11 in the zebra finch and turkey – two evolutionary distant birds.

Co-author from says that because birds lack the SP-D immune protein found in mammals, their lungs must rely on alternative defence strategies against respiratory pathogens.

“If we can identify how these proteins function in birds, we may be able to develop new strategies to improve immune responses in humans, particularly for respiratory diseases such as pneumonia and COVID-19,” Dr van Dijk says.

The researchers say the findings may provide a foundation for future medical and veterinary advances.

A video explaining the research is available at