LOS ANGELES, March 1 (Xinhua) -- Researchers at the U.S. National Institutes of Health (NIH) have identified antibodies targeting a hard-to-spot region of the influenza virus, the agency said on Friday.

The research results, published Friday in Immunity, sheds light on the relatively unexplored "dark side" of the neuraminidase (NA) protein head, said NIH.

Influenza NA is a surface protein containing a globular head portion and a narrow stalk portion. The underside of the NA head contains a highly conserved region with targets for antibodies that make it vulnerable to antibody binding and inhibition of the virus, as well as not being impacted by mutations common in drug-resistant strains, according to the study.

This region is termed the "dark side" due to its partially hidden location and relatively unexplored characteristics.

The researchers isolated human antibodies that target the NA dark side from the blood of two people who had recovered from influenza type A subtype H3N2, a major subtype of seasonal flu viruses. In lab tests, the antibodies inhibited propagation of viruses from subtype H2N2, the subtype that caused pandemic influenza in 1957-58, and H3N2 viruses from humans, swine, and birds.

The antibodies also protected mice from lethal infection by a subtype H3N2 virus when given to the animals either one day before or two days after infection, showing that the antibody may treat and prevent influenza in this model, according to the study.

These findings show that the NA dark side has unique, previously untapped epitopes that could be applied to the development of new vaccine and therapeutic strategies, said NIH.