title: Cryptococcal heat shock protein 70 homolog Ssa1 contributes to pulmonary expansion of Cryptococcus neoformans during the afferent phase of the immune response by promoting macrophage M2 polarization.
abstract: Numerous virulence factors expressed by Cryptococcus neoformans modulate host defenses by promoting nonprotective Th2-biased adaptive immune responses. Prior studies demonstrate that the heat shock protein 70 homolog, Ssa1, significantly contributes to serotype D C. neoformans virulence through the induction of laccase, a Th2-skewing and CNS tropic factor. In the present study, we sought to determine whether Ssa1 modulates host defenses in mice infected with a highly virulent serotype A strain of C. neoformans (H99). To investigate this, we assessed pulmonary fungal growth, CNS dissemination, and survival in mice infected with either H99, an SSA1-deleted H99 strain (Δssa1), and a complement strain with restored SSA1 expression (Δssa1::SSA1). Mice infected with the Δssa1 strain displayed substantial reductions in lung fungal burden during the innate phase (days 3 and 7) of the host response, whereas less pronounced reductions were observed during the adaptive phase (day 14) and mouse survival increased only by 5 d. Surprisingly, laccase activity assays revealed that Δssa1 was not laccase deficient, demonstrating that H99 does not require Ssa1 for laccase expression, which explains the CNS tropism we still observed in the Ssa1-deficient strain. Lastly, our immunophenotyping studies showed that Ssa1 directly promotes early M2 skewing of lung mononuclear phagocytes during the innate phase, but not the adaptive phase, of the immune response. We conclude that Ssa1's virulence mechanism in H99 is distinct and laccase-independent. Ssa1 directly interferes with early macrophage polarization, limiting innate control of C. neoformans, but ultimately has no effect on cryptococcal control by adaptive immunity.
authors.affiliation: Graduate Program in Immunology, University of Michigan, Ann Arbor, MI 48109; Veterans Affairs Hospital, Ann Arbor, MI 48105;
authors.forename: Alison J
authors.initials: AJ
authors.lastname: Eastman
authors.affiliation: Veterans Affairs Hospital, Ann Arbor, MI 48105; Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, MI 48109;
authors.forename: Xiumiao
authors.initials: X
authors.lastname: He
authors.affiliation: Veterans Affairs Hospital, Ann Arbor, MI 48105; Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, MI 48109;
authors.forename: Yafeng
authors.initials: Y
authors.lastname: Qiu
authors.affiliation: Veterans Affairs Hospital, Ann Arbor, MI 48105; Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, MI 48109;
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Davis
authors.affiliation: Veterans Affairs Hospital, Ann Arbor, MI 48105;
authors.forename: Priya
authors.initials: P
authors.lastname: Vedula
authors.affiliation: Veterans Affairs Hospital, Ann Arbor, MI 48105;
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Lyons
authors.affiliation: Laboratory of Clinical Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892;
authors.forename: Yoon-Dong
authors.initials: YD
authors.lastname: Park
authors.affiliation: Department of Biology, University of Texas at San Antonio, San Antonio, TX 78458; South Texas Center for Emerging Infectious Diseases, University of Texas at San Antonio, San Antonio, TX 78249; and.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Hardison
authors.affiliation: Veterans Affairs Hospital, Ann Arbor, MI 48105; Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, MI 48109;
authors.forename: Antoni N
authors.initials: AN
authors.lastname: Malachowski
authors.affiliation: Graduate Program in Immunology, University of Michigan, Ann Arbor, MI 48109; Veterans Affairs Hospital, Ann Arbor, MI 48105; Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, MI 48109;
authors.forename: John J
authors.initials: JJ
authors.lastname: Osterholzer
authors.affiliation: Department of Biology, University of Texas at San Antonio, San Antonio, TX 78458; South Texas Center for Emerging Infectious Diseases, University of Texas at San Antonio, San Antonio, TX 78249; and.
authors.forename: Floyd L
authors.initials: FL
authors.lastname: Wormley
authors.affiliation: Laboratory of Clinical Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892; Section of Infectious Diseases, Department of Medicine, University of Illinois at Chicago College of Medicine, Chicago, IL 60612.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Williamson
authors.affiliation: Graduate Program in Immunology, University of Michigan, Ann Arbor, MI 48109; Veterans Affairs Hospital, Ann Arbor, MI 48105; Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, MI 48109; olszewsm@umich.edu.
authors.forename: Michal A
authors.initials: MA
authors.lastname: Olszewski
mesh_terms: D056704:Adaptive Immunity; D000818:Animals; D001921:Brain / Q000378:metabolism / Q000382:microbiology / Q000473:pathology; D003453:Cryptococcosis / Q000276:immunology* / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D003455:Cryptococcus neoformans / Q000235:genetics / Q000378:metabolism*; D016207:Cytokines / Q000378:metabolism; D004195:Disease Models, Animal; D005260:Female; D015966:Gene Expression Regulation, Fungal; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D007113:Immunity, Innate; D042845:Laccase / Q000235:genetics / Q000378:metabolism; D007962:Leukocytes / Q000276:immunology / Q000473:pathology; D008172:Lung Diseases, Fungal / Q000276:immunology* / Q000382:microbiology* / Q000401:mortality / Q000473:pathology; D008262:Macrophage Activation / Q000276:immunology; D008264:Macrophages / Q000276:immunology*; D051379:Mice; D009154:Mutation
chemical_list: D016207:Cytokines; D018840:HSP70 Heat-Shock Proteins; D042845:Laccase