Cryptococcus neoformans is an opportunistic yeast that may produce a life-threatening meningitis in individuals with deficiencies in cell mediated immunity, including AIDS. The yeast is surrounded by a polysaccharide capsule that is essential to virulence. The primary constituent of the capsule is a polysaccharide termed glucuronoxylomannan (GXM). The capsule's ability to inhibit phagocytosis is its most important function. The overall goal of this study is to understand the cellular and molecular basis for inhibition of phagocytosis by the capsule. A library of GXM mAbs was generated during the current grant period. Depending on epitope specificity, a mAb can be highly opsonic or poorly opsonic. Such opsonization is not Fc dependent. Additional studies have found that the capsule is a matrix with a density that decreases in a near linear fashion as the capsule edge is approached. It is the overall hypothesis for this proposal that the position of binding of potentially opsonic ligands, e.g., antibody or opsonic fragments of C3 relative to the capular edge and the mobility of such ligands will determine whether or not the yeast will be ingested by phagocytes.
Specific Aim 1 will identify, at a molecular level, the antibody-capsule interactions that distinguish highly opsonic from weakly opsonic mAbs.
Aim 2 will assess the spatial relationship between GXM at the capsular edge and potentially opsonic ligands that are bound to the capsular matrix.
Aim 3 will examine the molecular mobility of GXM and potentially opsonic ligands at the capsular edge and the effects of highly opsonic and weakly opsonic mAbs on such mobility.
Aim 4 will identify structural components of GXM that are required for direct binding to macrophages.
Aim 5 will identify means to activate macrophages for increased uptake of unopsonized and iC3b-opsonized cryptococci. These studies will contribute to our understanding of a virulence factor that is common to many microbial pathogens and will identify means to enhance phagocytosis and host resistance to cryptococcosis.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
Project #
Application #
Study Section
Bacteriology and Mycology Subcommittee 2 (BM)
Program Officer
Duncan, Rory A
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Nevada Reno
Schools of Medicine
United States
Zip Code
Ezeanolue, Echezona E; Nwizu, Chidi; Greene, Gregory S et al. (2016) Brief Report: Geographical Variation in Prevalence of Cryptococcal Antigenemia Among HIV-Infected, Treatment-Naive Patients in Nigeria: A Multicenter Cross-Sectional Study. J Acquir Immune Defic Syndr 73:117-21
Davis, Michael J; Eastman, Alison J; Qiu, Yafeng et al. (2015) Cryptococcus neoformans-induced macrophage lysosome damage crucially contributes to fungal virulence. J Immunol 194:2219-31
Kozel, Thomas R; Wickes, Brian (2014) Fungal diagnostics. Cold Spring Harb Perspect Med 4:a019299
Gates-Hollingsworth, Marcellene A; Kozel, Thomas R (2013) Serotype sensitivity of a lateral flow immunoassay for cryptococcal antigen. Clin Vaccine Immunol 20:634-5
Hansen, Jessica; Slechta, E Susan; Gates-Hollingsworth, Marcellene A et al. (2013) Large-scale evaluation of the immuno-mycologics lateral flow and enzyme-linked immunoassays for detection of cryptococcal antigen in serum and cerebrospinal fluid. Clin Vaccine Immunol 20:52-5
Piccioni, M; Monari, C; Kenno, S et al. (2013) A purified capsular polysaccharide markedly inhibits inflammatory response during endotoxic shock. Infect Immun 81:90-8
Griffiths, Emma J; Hu, Guanggan; Fries, Bettina et al. (2012) A defect in ATP-citrate lyase links acetyl-CoA production, virulence factor elaboration and virulence in Cryptococcus neoformans. Mol Microbiol 86:1404-23
Jarvis, Joseph N; Percival, Ann; Bauman, Sean et al. (2011) Evaluation of a novel point-of-care cryptococcal antigen test on serum, plasma, and urine from patients with HIV-associated cryptococcal meningitis. Clin Infect Dis 53:1019-23
Percival, Ann; Thorkildson, Peter; Kozel, Thomas R (2011) Monoclonal antibodies specific for immunorecessive epitopes of glucuronoxylomannan, the major capsular polysaccharide of Cryptococcus neoformans, reduce serotype bias in an immunoassay for cryptococcal antigen. Clin Vaccine Immunol 18:1292-6
Piccioni, M; Monari, C; Bevilacqua, S et al. (2011) A critical role for FcgammaRIIB in up-regulation of Fas ligand induced by a microbial polysaccharide. Clin Exp Immunol 165:190-201

Showing the most recent 10 out of 94 publications