Severe pneumonia has three distinct subtypes with varying biological responses, a finding that helps explain why some patients recover quickly while in others the lung infection becomes fatal, researchers say.
On the surface, the 95 intensive-care-unit patients in the study appeared similarly ill, but their outcomes were very different, study leader Dr. Mark Jeffrey of the University of Cambridge said in a statement.
“It was only when we drilled down and looked at patterns of inflammation that the differences became apparent,” he said.
About half the patients mainly had immune-system suppression, significant damage to the lining of the lungs, and bleeding in the tiny air sacs in the lungs. These patients did not have many signs of inflammation, which may explain why anti-inflammatory medications can fail or even be harmful in some cases, the researchers reported in Nature Communications.
Another quarter of patients – those who were critically ill for the longest periods and spent the most time on mechanical ventilation - had severe and persistent inflammation, with a flood of immature immune cells in the lungs. They would be most likely to respond to anti-inflammatory treatments, the researchers said.
Finally, about a quarter of cases were characterized by a balanced immune response and active repair of damage to the lungs. These patients were most likely to recover faster and spend the shortest time on the ventilator, even though they initially appeared to be just as ill as the others.
“This helps explain why ‘one-size-fits-all’ treatments, including some immune-modulating drugs, have often failed in clinical trials,” Jeffrey said.
Senior study author Dr. Andrew Conway Morris of the University of Cambridge said failing to look at the disease's underlying biology risks missing important information.
“Instead of asking ‘Does this patient have pneumonia?’, we should be asking ‘What's the inflammatory pattern in this patient's lungs?’” Morris said.
Study coauthor Dr. Vilas Navapurkar from Addenbrooke's Hospital in Cambridge added, “If we know which subtype of pneumonia an individual has, we can potentially tailor their treatment more precisely, boosting the immune response in some, while calming harmful inflammation in others.”
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