All highly pathogenic avian influenza viruses are believed to arise from low pathogenic precursor viruses.
To shed more light on virulence determinants required for evolution of HPAIV which, in nature, derive from low-pathogenic precursors of subtypes H5 or H7 [9], [10] [11], [12], [13], [14], [15], [16], [16], we addressed the question whether a low-pathogenic avian strain of the H5N1 subtype would transform into a highly pathogenic strain after introduction of a polybasic HA cleavage site.
The hypothesis that HPAI H5 and H7 viruses emerge from low-pathogenic precursors only after the H5 and H7 LPAI precursors have been introduced into domestic poultry has been supported by work demonstrating that HPAI viruses do not appear to form separate phylogenetic lineages in waterfowl (3 ).
Taken together, acquisition of a polybasic HA cleavage site is only one necessary step for evolution of H5N1 HPAIV from low-pathogenic precursor strains, which may already have cryptic virulence potential.
It is not clear whether germline-encoded polyreactive autoantibodies are the precursors of pathogenic autoantibodies.
Therefore, to study whether environmental nonO1-nonO139 isolates, which are native to the aquatic ecosystem, act as precursors for pathogenic O1 strains, their virulence potential and evolutionary relatedness was checked.
In other influenza A strains, such as subtypes H5 and H7 from highly pathogenic viruses, the HA0 precursor carries a polybasic proteolytic site that is cleaved intracellularly in the trans-Golgi compartment by proteinases of the subtilisin family [20], [21].
Here, SIRT1 is involved in neuroprotective signaling, reducing the formation of β-amyloid, the pathogenic form of amyloid precursor protein (APP), one of the two main diagnostic histopathologies of AD, along with neurofibrillary tangles.
Tau hyperphosphorylation may be instrumental in the negative effects of stress and GC on cognition, initially by increasing the production of pathogenic products of amyloid precursor protein (APP), followed by up-regulation of Tau kinases such as GSK3β and cdk5 and aberrantly hyperphosphorylated Tau [ 199].
The polyreactive nature of this antibody, which will be examined in more depth in future studies, is potentially important since polyreactive antibodies have been shown to be the precursors of more pathogenic antibodies in lupus [33].
When these normal cellular prion precursors convert to pathogenic prion proteins, the transmissible conformations are characterized by β-pleated sheets rather than the normal α-helix structure, and they do not elicit an immune response (4 ).
