We. Swords et al., Binding of the non-typeable Haemophilus influenzae lipooligosaccharide to the PAF receptor initiates host cell signalling, CELL MICROB, 3(8), 2001, pp. 525-536
Non-typeable Haemophilus influenzae (NTHi) invades host cells by bidding, o
f the platelet-activating factor (PAF) receptor via lipooligosaccharide (LO
S) glycoforms containing phosphorylcholine (ChoP). The effect of NTHi infec
tion on host cell signalling and its role in NTHi invasion was examined. Th
e infection of human bronchial epithelial cells with NTHi 2019 increased cy
tosolic Ca2+ levels, and the invasion of bronchial cells by NTHi 2019 was I
nhibited by pretreatment with the cell-permeant intracellular Ca2+ chelator
BAPTA-AM (P = 0.022) or thapsigargin (P = 0.016). Cytosolic inositol phosp
hate (IP) levels were also increased after infection with NTH! 2019 (P < 0.
001), but not after infection with isogenic mutants expressing altered LOS
glycoforms lacking ChoP. PAF receptor antagonist reduced NTHi 2019-stimulat
ed IP production in a dose-dependent manner. NTH! 2019 invasion was inhibit
ed by pertussis toxin (PTX) and the phosphatidylinositol-3-kinase inhibitor
s wortmannin and LY294002. The less invasive strain NTHi 7502 also initiate
d IP production, but was unaffected by PAF receptor antagonist or PTX. Thes
e data demonstrate that the binding of the PAF receptor by NTHi initiates r
eceptor coupling to a PTX-sensitive heterotrimeric G protein complex, resul
ting in a multifactorial host cell signal cascade and bacterial invasion. M
oreover, the data suggest that NTHi strains initiate cell signalling and in
vade by different mechanisms, and that invasion mediated by PAF receptor ac
tivation is more efficient than macropinocytosis.