Biology Reference
In-Depth Information
No data have been published on the expression and localization
of receptors for minor group HRVs in the airway epithelium
in situ
.
LDLR expression has been solely studied in human tracheal epithelial
cell cultures. Similar to major group HRVs that stimulate ICAM-1
expression, HRV2 infection resulted in up-regulation of LDLR
mRNA and protein.
137,138
HRV2 infection was completely blocked by
an antibody against LDLR in tracheal cells. However, the situation
might differ in nasal epithelia, where VLDLR and/or LRP might be
present and implicated in viral attachment. In any case, the polarity of
receptor expression and virus entry and release are unexplored. It is
of note that infections by minor group HRV occur more frequently
than expected from the relative numbers of serotypes belonging to
the two groups. This might be taken to indicate higher concentra-
tions and/or higher efficiency of these receptors with respect to bind-
ing and internalization as compared to ICAM-1.
Concluding Remarks
Despite great effort to elucidate the early events of infection, such as
attachment to the host cells, penetration, and release of the viral genome
into the cytosol, many questions have remained open: (1) the basis for
the strict receptor specificity is unclear; (2) the structure, localization and
mode of receptor binding of major and minor group HRV
in vivo
is
completely unknown; (3) it is not understood why and how HRVs pen-
etrate into the cytoplasm by using different pathways; (4) it is poorly
understood why major group serotypes differ in their requirement for
low pH for structural modification and uncoating; (5) it is not known in
detail how the RNA genome is released and transferred into the cytosol;
and, most importantly, (6) the mechanism of infection of the airway
epithelium is largely unexplored with respect to receptor expression
per se,
polarity of virus entry and vectorial release of infectious virions.
Acknowledgments
This work was supported by grants from the Virology Foundation
(D.B. and R.F.) and from the Austrian Science Foundation (P-12967
