White blood cells could be good targets for future asthma drugs, US researchers hope.
The findings offer options for drug development
Two studies, at the Mayo Clinic and the Children's Hospital, Boston, found white cells called eosinophils play a role in causing asthma in mice.
The authors believe the same could be true in humans.
Their findings, reported in Science, contradict earlier research suggesting these cells are the result, rather than a cause, of asthma.
A study published in The Lancet journal in 2000 concluded eosinophils had no role in the development of asthma in humans.
Dr Marsha Wills-Karp, chair of the division of immunobiology at Cincinnati Children's Hospital, said: "Eosinophils had been one of the major targets of drug companies for years.
"It was very confusing and disheartening to many people when this study in humans did not support this line of development.
"The new studies clearly show evidence that eosinophils have a role in asthma," she said.
Both studies were based on experiments using mice lacking eosinophils.
In the first, Dr James Lee and his team at the Mayo Clinic found eosinophils were essential for asthma to develop.
The mice without these cells developed no symptoms when exposed to known allergic triggers of asthma.
The second study, Dr Alison Humbles and colleagues from the Children's Hospital, Boston, found eosinophils were important in one of the long-term parts of the asthma disease process which affects the structure of the lungs.
Commenting on both studies, Dr Wills-Karp said: "Targeting eosinophils may well provide effective therapy for a subset of asthma patients."
Dr Matthew Hallsworth from Asthma UK, said: "Over the last few years trials of potential therapeutic proteins and antibodies have been effective at reducing eosinophil numbers, but this did not appear to translate into improvements in asthma symptoms.
"Consequently trials such as these called into question the central role of the eosinophil in asthma.
"The findings from these new studies re-establish the importance of the eosinophil as a potential therapeutic target in asthma and the continuing debate shows we still have much to understand about the complexities of airway inflammation in asthma."
Dr Peter Howarth, chairman of Allergy UK and respiratory allergy specialist at Southampton Hospital, said: "Studies such as these add to the body of information but have to be taken with caution as animal studies historically have not proved to be ideal models for human asthma."