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Infection and Immunity, September 1999, p. 4477-4484, Vol. 67, No. 9
Department of Microbiology and Immunology,
Temple University School of Medicine, Philadelphia, Pennsylvania
19140,1 and the Department of
Microbiology and Immunology, Finch University of the Health
Sciences, Chicago Medical School, North Chicago, Illinois
600642
Received 13 November 1998/Returned for modification 5 January
1999/Accepted 16 June 1999
The most abundant protein on the surface of the promastigote form
of the protozoan parasites Leishmania spp. is a 63-kDa
molecule, designated gp63 or leishmanolysin. Because gp63 has been
shown to possess fibronectin-like properties, we examined the
interaction of gp63 with the cellular receptors for fibronectin. We
measured the direct binding of Leishmania to human
macrophages or to transfected mammalian cells expressing human
fibronectin receptors. Leishmania expressing gp63 exhibited
modest but reproducible adhesion to human macrophages and to
transfected CHO cells expressing
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Copyright © 1999, American Society for Microbiology. All rights reserved.
Interaction of Leishmania gp63 with
Cellular Receptors for Fibronectin

4/
1 fibronectin receptors. In
both cases, this interaction depended on gp63 but occurred
independently of the SRYD sequence of gp63, because parasites
expressing gp63 with a mutated SRYD sequence bound to macrophages and
4/
1 receptor-expressing cells as well as did wild-type parasites.
The contribution of gp63 to parasite adhesion was more pronounced when
the assays were performed in the presence of complement, suggesting
that the receptors for complement and fibronectin may cooperate to
mediate the efficient adhesion of parasites to macrophages. The
interaction of gp63 with fibronectin receptors may also play an
important role in parasite internalization by macrophages. Erythrocytes
to which gp63 was cross-linked were efficiently phagocytized by
macrophages, whereas control erythrocytes opsonized with complement
alone bound to macrophages but remained peripherally attached to the
outside of the cell. Similarly, parasites expressing wild-type gp63
were rapidly and efficiently phagocytized by resting macrophages,
whereas parasites lacking gp63 were internalized more slowly. This
rapid internalization of gp63-expressing parasites was dependent on the
1 integrins, because pretreatment of macrophages with monoclonal antibodies to the
1 integrins decreased the internalization of gp63-expressing parasites. These observations indicate that complement receptors are the primary mediators of parasite adhesion; however, maximal parasite adhesion and internalization may require the participation of the
1 integrins, which recognize fibronectin-like molecules such as gp63 on the surface of the parasite.
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Temple University School of Medicine, 3400 N. Broad St., Philadelphia, PA 19140. Phone: (215) 707-8262. Fax: (215)
707-7788. E-mail: dmmosser{at}astro.temple.edu.
Present address: Department of Internal Medicine, University of
Iowa College of Medicine, Iowa City, IA 52242.
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