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Infect. Immun., 03 1997, 931-935, Vol 65, No. 3
SM Levitz, A Tabuni, TR Kozel, RS MacGill, RR Ingalls and DT Golenbock
Previously, we demonstrated that monoclonal antibodies (MAb) directed
against any of the three defined complement receptors (CR) for the third
component of complement (CR1, CR3, and CR4) profoundly inhibited the
binding of serum-opsonized Cryptococcus neoformans to monocyte- derived
macrophages. These studies suggested either that a synergistic interaction
between multiple CR was required for optimal binding of C. neoformans or
that the MAb were exerting nonspecific effects (such as receptor
coassociation). In the present studies, we took a novel approach to
dissecting out the contributions of individual receptors to binding of a
microbial pathogen. Chinese hamster ovary (CHO) cells stably transfected
with human CR1, CR3, or CR4 were challenged with serum-opsonized C.
neoformans. We found that CHO cells transfected with any of the three
receptors bound C. neoformans, with the avidity of binding to CR3 being the
greatest followed in decreasing order by CR1 and CR4. Following binding of
C. neoformans to transfected CHO cells, most organisms remained surface
attached only, although for each receptor a significant percentage (18.5 to
27.3%) of C. neoformans was internalized. Both C. neoformans and sheep
erythrocytes that were selectively opsonized with the fragments of the
third component of complement, C3b and iC3b, were bound preferentially by
CHO cells transfected with CR1 and CR3, respectively. These data establish
CR1, CR3, and CR4 as receptors independently capable of binding C.
neoformans opsonized with fragments of C3. Moreover, our study demonstrates
the usefulness of transfected cell lines as a powerful tool for identifying
the contribution of individual receptors to the binding of a microbial
pathogen.
Copyright © 1997, American Society for Microbiology
Binding of Cryptococcus neoformans to heterologously expressed human complement receptors
Evans Memorial Department of Clinical Research, Boston Medical Center, Massachusetts 02118, USA. slevitz@med-med1.bu.edu
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