Media playback is unsupported on your device Media caption Medical Research Council animation shows how the body fights viruses

Scientists say they have made a landmark discovery which could pave the way for new drugs to beat illnesses like the common cold.

Until now experts had thought that antibodies could only tackle viral infections by blocking or attacking viruses outside cells.

But work done by the Medical Research Council shows antibodies can pass into cells and fight viruses from within.

PNAS journal said the finding held promise for a new antiviral drugs.

The Cambridge scientists stressed that it would take years of work and testing to find new therapies, and said that the pathway they had discovered would not work on all viruses.

Fighting viruses

Some antiviral drugs are already available to help treat certain conditions, like HIV.

But viruses remain mankind's biggest killer, responsible for twice as many deaths each year as cancer, and are among the hardest of all diseases to treat.

The new discovery by Dr Leo James and colleagues transforms the previous scientific understanding of our immunity to viral diseases like the common cold, 'winter vomiting' and gastroenteritis.

It shows that antibodies can enter cells and that once inside, they then trigger a response, led by a protein called TRIM21.

Doctors have plenty of antibiotics to fight bacterial infections but few antiviral drugs Dr Leo James, Lead researcher at the MRC in Cambridge

This protein pulls the virus into a disposal system used by the cell to get rid of unwanted material.

The researchers found this process happens quickly, usually before most viruses have chance to harm the cell.

And they discovered that increasing the amount of TRIM21 protein in cells makes this process even more effective, suggesting new ways of making better antiviral drugs.

Dr James said: "Doctors have plenty of antibiotics to fight bacterial infections but few antiviral drugs.

"Although these are early days, and we don't yet know whether all viruses are cleared by this mechanism, we are excited that our discoveries may open multiple avenues for developing new antiviral drugs."

Sir Greg Winter, deputy director of the MRC Laboratory of Molecular Biology, said: "This research is not only a leap in our understanding of how and where antibodies work, but more generally in our understanding of immunity and infection."