Optimized GAPDH-truncated immunogen of Streptococcus equi elicits an enhanced immune response and provides effective protection in a mouse model.

Strangles is an acute and frequently diagnosed infectious disease caused by Streptococcus equi subsp. equi. Infection with this pathogen can cause grave losses to the equine industry. The present work investigates glyceraldehyde-3-phosphate dehydrogenase (GAPDH), an important surface-localized virulence factor of S. equi, to determine whether it could be developed into an efficacious and suitable subunit vaccine against strangles. Two different recombinant fragments of S. equi GAPDH, namely, GAPDH-L and GAPDH-S, were constructed and expressed. Further, the antigenicity and immunogenicity of these two recombinant proteins were compared and evaluated in a mouse model. Our results revealed that immune responses were efficiently induced by the proteins in immunized mice. Remarkably, higher survival rates and significantly lower bacterial loads in the lung, liver, kidney, and spleen were observed in the GAPDH-S group compared with the GAPDH-L group after challenge with S. equi. High levels of specific antibodies, elevated antibody titers, and increased proportions of CD8 + T cells further indicated that GAPDH-S elicited better humoral and cellular immune responses than GAPDH-L. Furthermore, the induction of TCR, TLR-2, TLR-3, and TLR-4 significantly increased in the GAPDH-S group compared with those in the GAPDH-L and negative control groups. In summary, our results indicate that the optimized recombinant protein GAPDH-S is a promising candidate construct that may be further developed into a multivalent subunit vaccine for strangles.

Analysis of a point mutation in H5N1 avian influenza virus hemagglutinin in relation to virus entry into live mammalian cells.

Binding to and infection of human cells is essential for avian influenza virus transmission. Since virus binding is not always predictive for efficient infection of the cells, here we wished to investigate how hemagglutinin (HA) mutations of avian influenza virus H5N1 influence virus post-binding events in a single cycle of replication. One mutation observed in H5 HA of avian and natural human isolates from mainland China, Hong Kong, Vietnam and Thailand was identified and analyzed. The effects of the mutation on receptor binding, fusion and virus entry into cultured cells were investigated using hemadsorption, polykaryon formation and pseudotyped virus that express luciferase in the cytoplasm of transduced cell. Our results revealed that replacing aspartic acid at residue 94 with asparagine enhanced virus fusion activity and increased the binding of HA to sialic acid alpha2,6 galactose, while it decreased pseudotyped virus entry into cells expressing the avian type receptor, sialic acid alpha2,3 galactose. Our result may have implications for the understanding of the role of HA mutations in virus entry into live cells that exclusively display one type of receptor.