PI3Kdelta regulation of influenza virus morbidity

Because influenza virus infection is an important cause of morbidity and mortality in the elderly and current vaccines have limited efficacy in the elderly and very young, it is imperative that new therapeutic approaches are developed to reduce pathogenesis associated with influenza virus infection. To achieve this, a greater understanding of the virus host interaction and the effects of ageing on the immune system are necessary. Devising strategies to reduce the inflammation associated with influenza virus infection would reduce morbidity. We propose to examine the role of a protein molecule called PI3K in inflammation and viral replication during influenza virus infection in aged mice. Using mice in which PI3K is modified in specific cell types we will identify potential PI3K targets that ameliorate the morbidity associated with influenza virus infection. Our preliminary data indicate that influenza virus infected PI3K-/-mice have a reduced lung cellular infiltrate and a reduced morbidity (weight loss) compared to influenza virus infected control mice, while viral replication is reduced and viral clearance remains unaffected. The studies proposed here will examine the how PI3K inhibition reduces morbidity in animals and the underpinning mechanism at the cellular and molecular level. Our application has important translational potential because it will identify targets to reduce influenza virus associated morbidity. The identification and validation of such targets is essential as resistance to existing antiviral is spreading.

Seasonal influenza virus infections affect 5-15% of human population and can result in death due to severe pneumonia, multiple organ failure and acute respiratory distress-like syndrome. The vast majority (90%) of the deaths per year that occur due to seasonal influenza virus infection are in individuals 65 years old or older. However pandemic strains appear to cause significant morbidity in the young. Although, the exact mechanism of influenza virus pathogenicity is unknown, the induction of an overreacting immune response is the likely cause.

Phosphoinositide 3-kinases (PI3K) are a family of enzymes involved in signal transduction and play a important role in immune cell function and development. PI3K may also be utilized by influenza virus to enhance viral replication. We have found that mice that have an inactivating mutation in the PI3K isoform p110delta(p110delta-/- mice) manifest significantly reduced morbidity after influenza type A virus infection compared to wild-type C57BL/6 mice.

The numbers of lung infiltrating activated CD8+ T cells and NK cells, granulocytes, macrophages and CD11c+CD11b+ dendritic cells (DC) are significantly reduced in influenza virus infected p110delta-/- mice. Despite this, viral clearance is not delayed in p110delta-/- mice, which actually have 10-fold lower lung viral titers than controls. These studies suggest that p110delta may play a critical role in influenza virus induced lung inflammation and morbidity and may contribute to viral replication.


In this proposal we will test the hypotheses that P110delta plays an important role in the pathogenesis of influenza type A virus infection and determine the mechanism by which p110delta deficiency protects mice from morbidity induced by influenza virus infection. We will make use of a novel conditional allele of P110delta that we have developed and validated. This will allow examination of the contribution of P110delta in the T cell lineage using CD4 Cre; in the B cell lineage using CD19Cre; and in lung epithelial cells using SPC-Cre.

The specific aims are:

Aim1. Determine whether P110delta deficiency in T cells affects virus-specific immunity.

Aim2. Investigate whether inactivation of P110delta in B cells affects virus-specific immunity.

Aim3. Investigate whether P110delta is required in viral production by epithelial cells.