Credit: Courtesy of Douglas C. Woodhams

The tree frog Litoria genimaculata (pictured in its habitat in the Australian rainforest) is not an obvious choice of laboratory animal. But skin secretions of such amphibians could be a rich source of antimicrobial peptides with activity against HIV (J. Virol. 79, 11598–11606).

Antimicrobial peptides are natural antibiotics, providing a first line of attack against microorganisms invading body fluids and skin. 880 such peptides have been isolated from species as diverse as spiders, scorpions, fruitflies and fish—and more than 20% are produced by the skin glands of frogs and toads.

Certain peptides such as human defensins are already known to have anti-HIV activity, but Scott VanCompernolle et al. explored whether any amphibian peptides would also block HIV infection. Screening a panel of 14 frog peptides, they found two that blocked HIV-1 infection of T cells, apparently by disrupting the viral envelope and preventing fusion with the target cell.

The peptides also had an unusual effect on infected dendritic cells. Dendritic cells are thought to capture and internalize HIV particles at mucosal surfaces, and then transfer the virus particles to T cells—the primary target of HIV infection. The frog peptides blocked this transfer—even when applied transiently to dendritic cells eight hours after HIV infection. How the peptides do this remains to be seen, but the study illustrates the largely untapped wealth of natural antimicrobial resources that could be explored for activity against human pathogens.