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Infect Immun, February 1998, p. 664-669, Vol. 66, No. 2
Microbiology Section, Department of
Experimental Medicine and Biochemical Sciences, University of Perugia,
Perugia, Italy,1 and
Department of
Microbiology, University of Nevada School of Medicine, Reno, Nevada
89557-004622
Received 18 September 1997/Returned for modification 21 October
1997/Accepted 21 November 1997
This report examines the effect of the major capsular
polysaccharide of Cryptococcus neoformans,
glucuronoxylomannan (GXM), on the antigen-presenting capability of
human monocytes treated with acapsular cells of C. neoformans. We found that pretreatment of acapsular cryptococci
with GXM downregulates, in a dose-dependent manner, the
antigen-presenting capacity of monocytes, leading to reduced
proliferative T-lymphocyte responses. Similar levels of suppression
occurred when monocytes were exposed to encapsulated cryptococci or
acapsular cryptococci that were pretreated with GXM. The magnitude of
the T-cell response correlated with the ability of monocytes to ingest
the yeast. Supernatant fluids from cocultures of monocytes and T cells
cultured with encapsulated cryptococci contained higher levels of
interleukin-10 (IL-10) than supernatant fluids of cells with acapsular
cryptococci. Addition of anti-IL-10 monoclonal antibodies to the
incubation medium of monocytes and T cells cultured with encapsulated
cryptococci restored proliferative T-cell responses to levels observed
during culture with acapsular cryptococci. Finally, treatment of
monocytes with encapsulated cryptococci or GXM-treated acapsular
cryptococci suppressed expression of class II major histocompatibility
complex (MHC) molecules in a manner consistent with previous reports of IL-10-mediated suppression of class II MHC molecules and suppression of
proliferative T-cell responses. These results suggest a link between
GXM encapsulation, increased IL-10 synthesis by monocytes, decreased
expression of class II MHC molecules on monocytes, and reduced
proliferative T-cell responses.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Encapsulation of Cryptococcus neoformans with
Glucuronoxylomannan Inhibits the Antigen-Presenting Capacity of
Monocytes
*
Corresponding author. Mailing address: Microbiology
Section, Department of Experimental Medicine and Biochemical Sciences, University of Perugia, Via del Giochetto, 06122 Perugia, Italy. Phone:
0039-75-585-3407. Fax: 0039-75-585-3400. E-mail:
vecchiar{at}unipg.it.
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