Chiara Luberto, Beatriz Martinez-Mariño, Daniel Taraskiewicz, Benjamin Bolaños, Pasquale Chitano, Dena L. Toffaletti, Gary M. Cox, John R. Perfect, Yusuf A. Hannun, Edward Balish, Maurizio Del Poeta
J Clin Invest.
2003;
112(7):1080–1094
doi:10.1172/JCI18309
This article Copyright © 2003, The American Society for Clinical Investigation
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i>Cryptococcus neoformans is a fungal pathogen that, after inhalation, can disseminate to the brain. Host alveolar macrophages (AMs) represent the first defense against the fungus. Once phagocytosed by AMs, fungal cells are killed by a concerted mechanism, involving the host-cellular response. If the cellular response is impaired, phagocytosis of the fungus may be detrimental for the host, since C. neoformans can grow within macrophages. Here, we identified a novel cryptococcal gene encoding antiphagocytic protein 1 (App1). App1 is a cryptococcal cytoplasmic protein that is secreted extracellularly and found in the serum of infected patients. App1 does not affect melanin production, capsule formation, or growth of C. neoformans. Treatment with recombinant App1 inhibited phagocytosis of fungal cells through a complement-mediated mechanism, and Δapp1 mutant is readily phagocytosed by AMs. Interestingly, the Δapp1 mutant strain showed a decreased virulence in mice deficient for complement C5 (A/Jcr), but it was hypervirulent in mice deficient for T and NK cells (Tgε26). This study identifies App1 as a novel regulator of virulence for C. neoformans, and it highlights that internalization of fungal cells by AMs increases the dissemination of C. neoformans when the host cellular response is impaired.
Figure 7
Histopathology of lungs and brains from animal models. (a–d, i–l, q–t, and u–x) PAS-positive staining. (e–h and m–p) Hematoxylin and eosin staining. Histopathology of lung from A/Jcr (a–d and e–h) and Tgε26 (i–l and m–p) is shown. Normal lung (a, e, i, and m) and lungs infected with C. neoformans WT (b, f, j, and n), GAL7:IPC1 (c, g, k, and o), and Δapp1 (d, h, l, and p) at 5 (a–d) and 15 (e–h) days and at 6 (i–l) and 13 (m–p) days after infection are shown. In the A/Jcr mouse model, a mucus hyperplasia/metaplasia (PAS-positive material) is present in lungs infected with the GAL7:IPC1 (c) and Δapp1 (d) strains (red arrowheads, c and d), but not in the lung infected with the WT strain (b). At day 15 of infection (e–h), intense neutrophil recruitment is observed in lung infected with the WT strain (orange arrowheads and orange circle, f), whereas neutrophils and macrophages are found in lung infected with the GAL7:IPC1 strain (orange arrowheads and green arrowheads, g) or neutrophils and lymphocytes are found in lung infected with the Δapp1 strain (orange arrowhead and violet arrowheads, h). At day 6 of infection in the Tgε26 mouse model (i–l), no mucus hyperproduction was observed (j–l and data not shown). Instead, dissemination of C. neoformans within macrophages in brown fat and lymphoid tissue was observed with the WT strain (green arrowhead, j) and, more pronounced, with the Δapp1 strain (green arrowhead and green circle, l) but not with the GAL7:IPC1 strain (k). At day 13 of infection (m–p), the inflammatory response against WT, GAL7:IPC1, and Δapp1 is mainly represented by macrophages (green arrowheads, n–p). The Δapp1 yeast cells are found mainly in brown fat (p). Histopathology of brains from A/Jcr (q–t) and Tgε26 (u–x) mice at days 15 and 13 of infection, respectively. Normal brains (q and u) and brains infected with WT (r and v), GAL7:IPC1 (s and w), and Δapp1 (t and x) are shown. C. neoformans cells were found in brains infected with the WT strain (r and v), whereas no yeast cells were found in brain sections examined from mice infected with the GAL7:IPC1 strain (s and w). The Δapp1 yeast cells were not found in brain sections examined from A/Jcr brain (t), whereas numerous Δapp1 cells were found in Tgε26 infected brain (x). Additionally, an Δapp1 yeast cell was found inside a macrophage (stained brown with anti-CD68 antibody) in a blood vessel of brain tissue at day 6 of infection (inset in x). (j, l, p, and x) In the insets, black arrowheads indicate yeast cells inside macrophages. (f and g) Yellow arrowheads indicate eosinophils. (c, d, f–h, and n–p) Insets are magnifications of small squared area. (r) Inset represents PAS staining of a different brain section. (x) Inset represents immunohistochemistry with anti-CD68 antibody for macrophage staining. Histology studies were also performed using IPC1Rec and Δapp1Rec strains, showing a phenotype similar to that observed with the WT strain (data not shown). Magnification, ×40. The images are representative of three different organ sections.
