Pore-forming toxins, such as aerolysin, are a largest group of bacterial virulent factors in pathogenic infections, which could oligomerize and form pores to the host-cell membranes, and therefore cause cellular lesions. Although it has been known that aerolysin-like proteins are also widely distribute in vertebrates, their biological functions are poorly known.

Most recently, Prof. ZHANG Yun (Kunming Institute of Zoology, CAS) and his colleagues has for the first time demonstrated that the host-derived aerolysin-like proteins play important roles in defending microbial infections.  

In the previous studies of Prof. ZHANG, they have successfully insolated and cloned a complex of bacterial pore-froming toxin aerolysin-like protein and trefoil factor (βγ-CAT) from secretions of the large-webbed bell toad (Bombina maxima). In this study, the biological functions of βγ-CAT has been further investigated. The results showed that under the bacterial challenge, the βγ-CAT protein expressions increased significantly in both the blood and the immune-related tissues in frogs. Meanwhile, when βγ-CAT was administrated in peritoneal infected mice and frogs, it greatly accelerated bacterial clearance and thus decreased animal mortalities.

“We believe that in the battle of bacterial infection and host dependence, βγ-CAT functions like a mutual weapon used by both the invader and the host”, according to Prof. ZHANG.

In this study, it was hypothesized that βγ-CAT oligomerizes along the endo-lysosome pathway to trigger lysosome destabilization and lead to interleukin-1β maturation and secretion via inflammasome activation.

This study enriched our knowledge of innate immune responding in vertebrates. More importantly, due to the similarities of the frog immune system to that of mammals, this study may eventually help to illustrate human pathophysiological mechanisms and to develop novel therapeutics. The details could be found in Proceedings of the National Academy of the Sciences, USA  

(http://www.pnas.org/content/early/2014/04/10/1321317111.abstract).