One of the key pathophysiologies of H5N1
infection is excessive proinflammatory
cytokine response (
cytokine storm) characterized by increases in IFN-β, TNF-α,
IL-6, CXCL10, CCL4, CCL2 and CCL5 in the respiratory tract. H5N1-induced
cytokine release can occur via an
infection-independent mechanism, however, detail of the cellular signaling involved is poorly understood. To elucidate this mechanism, the effect of inactivated (β-
propiolactone-treated) H5N1 on the
cytokine and
chemokine mRNA expression in 16HBE14o- human respiratory epithelial cells was investigated. We found that the inactivated-H5N1 increased
mRNA for
IL-6 and CXCL8 but not TNF-α, CCL5 or CXCL10. This effect of the inactivated-H5N1 was inhibited by
sialic acid receptor inhibitor (α-2,3 sialidase),
adenosine diphosphatase (
apyrase), P2Y receptor (P2YR) inhibitor (
suramin), P2Y6R antagonist (
MRS2578),
phospholipase C inhibitor (
U73122),
protein kinase C inhibitors (BIM and Gö6976) and cell-permeant Ca2+
chelator (
BAPTA-AM). Inhibitors of MAPK signaling, including of ERK1/2 (
PD98059),
p38 MAPK (
SB203580) and JNK (
SP600125) significantly suppressed the inactivated-H5N1-induced
mRNA expression of CXCL8. On the other hand, the inactivated-H5N1-induced
mRNA expression of
IL-6 was inhibited by
SB203580, but not
PD98059 or
SP600125, whereas SN-50, an inhibitor of NF-κB, inhibited the effect of virus on
mRNA expression of both of
IL-6 and CXCL8. Taken together, our data suggest that, without
infection, inactivated-H5N1 induces
mRNA expression of
IL-6 and CXCL8 by a mechanism, or mechanisms, requiring interaction between
viral hemagglutinin and α-2,3
sialic acid receptors at the cell membrane of host cells, and involves activation of P2Y6
purinergic receptors.