title: App1: an antiphagocytic protein that binds to complement receptors 3 and 2.
abstract: In previous studies, we showed that the pathogenic fungus Cryptococcus neoformans (Cn) produces a specific and unique protein called antiphagocytic protein 1 (App1), which inhibits phagocytosis of Cn by alveolar macrophages (AMs). Phagocytosis of Cn by AMs occurs mainly through a complement- or Ab-mediated mechanism. Among AM receptors, complement receptor 3 (CR3) and FcRgamma are the most common receptors involved in the phagocytic process. Because App1 inhibits phagocytosis of complement- but not Ab-coated erythrocytes, we investigated the role of CR3 in App1-macrophage interactions. We found that App1 binds to CR3 and if CR3 is absent from the surface of AMs, its antiphagocytic action is lost. When we investigated whether App1 would also bind to other complement receptor(s), we found that App1 does bind to complement receptor 2 (CR2) in a dose-dependent manner. In certain lymphoma cell lines, cellular proliferation is stimulated by complement through CR2, providing a potential use of App1 as a proliferation inhibitor of these cells. Initially discovered as an antiphagocytic protein regulating CR3-mediated innate immunity, App1 may also play a key role in the regulation of acquired immunity, because CR2 is mainly localized on B cells.
authors.affiliation: Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425.
authors.forename: Paola
authors.initials: P
authors.lastname: Stano
authors.affiliation: Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425.
authors.forename: Virginia
authors.initials: V
authors.lastname: Williams
authors.affiliation: Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425.
authors.forename: Maristella
authors.initials: M
authors.lastname: Villani
authors.affiliation: Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425.
authors.forename: Eugene S
authors.initials: ES
authors.lastname: Cymbalyuk
authors.affiliation: Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425.
authors.forename: Asfia
authors.initials: A
authors.lastname: Qureshi
authors.affiliation: Microbiology and Immunology, Medical University of South Carolina, Charleston, SC 29425.
authors.forename: Yuxiang
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Dipartimento di Sanita' Pubblica, Microbiologia-Virologia, Universita' degli Studi di Milano, Milan, Italy.
authors.forename: Giulia
authors.initials: G
authors.lastname: Morace
authors.affiliation: Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425.
authors.forename: Chiara
authors.initials: C
authors.lastname: Luberto
authors.affiliation: Microbiology and Immunology, Medical University of South Carolina, Charleston, SC 29425.
authors.forename: Stephen
authors.initials: S
authors.lastname: Tomlinson
authors.affiliation: Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425.|Microbiology and Immunology, Medical University of South Carolina, Charleston, SC 29425.|Division of Infectious Diseases, Medical University of South Carolina, Charleston, SC 29425.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Del Poeta
mesh_terms: D000818:Animals; D000908:Antibodies, Fungal / Q000096:biosynthesis / Q000378:metabolism; D000911:Antibodies, Monoclonal / Q000378:metabolism; D016466:CHO Cells; D002352:Carrier Proteins / Q000276:immunology / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D003455:Cryptococcus neoformans / Q000276:immunology* / Q000472:pathogenicity*; D005656:Fungal Proteins / Q000276:immunology / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D016177:Macrophage-1 Antigen / Q000235:genetics / Q000378:metabolism*; D016676:Macrophages, Alveolar / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010587:Phagocytosis / Q000235:genetics / Q000276:immunology*; D011485:Protein Binding / Q000276:immunology; D017464:Receptors, Complement 3d / Q000378:metabolism*
chemical_list: D000908:Antibodies, Fungal; D000911:Antibodies, Monoclonal; C535050:App1 protein, Cryptococcus neoformans; D002352:Carrier Proteins; D005656:Fungal Proteins; D016177:Macrophage-1 Antigen; D017464:Receptors, Complement 3d