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Infect. Immun., Apr 1997, 1211-1216, Vol 65, No. 4
T Hayashi, SP Rao and A Catanzaro
Attachment to and uptake by host cells are important early events in the
pathogenesis of intracellular organisms such as Mycobacterium avium.
Monocyte-derived macrophages (MDM) are known to express multiple surface
receptors that play a role in binding to and uptake of M. avium. These
include complement receptor type 3 (CR3), fibronectin receptor, mannose
receptor, and transferrin receptor. In addition to these, we have
previously reported that the integrin receptor alpha(v)beta3 also plays a
role in binding to M. avium in a nonopsonic environment. Further, we have
shown that a 68-kDa surface protein of M. avium binds to human monocytes
and plays a role in attachment of M. avium to MDM. The present study
provides direct evidence that this protein mediates attachment of M. avium
to MDM by binding to alpha(v)beta3. Using the technique of cell surface
enzyme-linked immunosorbent assay, we have shown that the M. avium 68-kDa
protein inhibits the binding of monoclonal antibodies (MAb) against
alpha(v)beta3 to MDM compared to control proteins such as ovalbumin and
laminin (P < 0.05). Dual-labeling studies were performed to demonstrate
that after phagocytosis, alpha(v)beta3 is present along with M. avium in
phagosomes of M. avium-infected MDM. In addition, we have demonstrated that
this interaction between alpha(v)beta3 and the M. avium 68-kDa protein
resulted in enhancement of CR3 expression, which is known to play a role in
complement-mediated uptake of M. avium. Attachment of MDM to wells coated
with the M. avium 68-kDa protein resulted in a twofold increase in CR3
expression compared to attachment of MDM to wells coated with ovalbumin.
This enhancement was completely inhibited by pretreatment of MDM with MAb
against alpha(v)beta3. In summary, M. avium binds to MDM via alpha(v)beta3
with the help of the M. avium 68-kDa protein, and this ligation enhanced
the expression of CR3 on MDM. Since CR3 has been known to play a role in M.
avium uptake, enhanced expression of this receptor mediated by M.
avium-alpha(v)beta3 interaction indicates a complex mechanism of
communication among different receptors that participate in M. avium
attachment and uptake. These findings add to current understanding of the
roles played by multiple receptor-ligand systems in uptake and pathogenesis
of intracellular pathogens such as M. avium.
Copyright © 1997, American Society for Microbiology
Binding of the 68-kilodalton protein of Mycobacterium avium to alpha(v)beta3 on human monocyte-derived macrophages enhances complement receptor type 3 expression
UCSD Medical Center, University of California, San Diego, 92103-8374, USA.
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