Induction of heterosubtypic cross-protection against influenza by a whole inactivated virus vaccine: the role of viral membrane fusion activity

BACKGROUND

The inability of seasonal influenza vaccines to effectively protect against infection with antigenically drifted viruses or newly emerging pandemic viruses underlines the need for development of cross-reactive influenza vaccines that induce immunity against a variety of virus subtypes. Therefore, potential cross-protective vaccines, e.g., whole inactivated virus (WIV) vaccine, that can target conserved internal antigens such as the nucleoprotein (NP) and/or matrix protein (M1) need to be explored.

METHODOLOGY/PRINCIPAL FINDINGS

In the current study we show that a WIV vaccine, through induction of cross-protective cytotoxic T lymphocytes (CTLs), protects mice from heterosubtypic infection. This protection was abrogated after depletion of CD8+ cells in vaccinated mice, indicating that CTLs were the primary mediators of protection. Previously, we have shown that different procedures used for virus inactivation influence optimal activation of CTLs by WIV, most likely by affecting the membrane fusion properties of the virus. Specifically, inactivation with formalin (FA) severely compromises fusion activity of the virus, while inactivation with β-propiolactone (BPL) preserves fusion activity. Here, we demonstrate that vaccination of mice with BPL-inactivated H5N1 WIV vaccine induces solid protection from lethal heterosubtypic H1N1 challenge. By contrast, vaccination with FA-inactivated WIV, while preventing death after lethal challenge, failed to protect against development of disease and severe body weight loss. Vaccination with BPL-inactivated WIV, compared to FA-inactivated WIV, induced higher levels of specific CD8+ T cells in blood, spleen and lungs, and a higher production of granzyme B in the lungs upon H1N1 virus challenge.

CONCLUSION/SIGNIFICANCE

The results underline the potential use of WIV as a cross-protective influenza vaccine candidate. However, careful choice of the virus inactivation procedure is important to retain membrane fusion activity and full immunogenicity of the vaccine.

[Influence of cross-protection on the survival of Lactobacillus casei ATCC 393]

OBJECTIVE

In this study, we investigated the cross-protection of Lactobacillus casei ATCC 393 under multi-stress conditions.

METHODS

Cells pre-adapted to mild conditions (heat, H2O2, acid or bile salts) were then treated at lethal temperature (> 60 degrees C) or hydrogen peroxide stress (> 5 mmol/L). Furthermore, the changes of survival rate intracellular pH and membrane fatty acid under lethal conditions with or without acid adaption were compared.

RESULTS

The cross-protection in Lactobacillus casei ATCC 393 were affected by different stress conditions. Acid pre-adaption, especially hydrochloride treatment, would increase the resistance of cells to lethal heat and peroxide stresses significantly, with the survival rate of 305-fold and 173-fold, respectively. Further study suggested that the effect of acid pre-adaption might be related to the regulation on intracellular pH and the saturation of cell membrane.

CONCLUSION

Hydrochloride adaption was the best inducer for the cross-protection of Lactobacillus casei ATCC 393 to maintain relatively stable physiological status of cells. The results supplied a novel way to investigate the relationship between different protective mechanisms in L. casei under different kinds of stresses.