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Infection and Immunity, June 1999, p. 3096-3107, Vol. 67, No. 6
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

In Vitro and In Vivo Stability a Cryptococcus neoformans Glucuronoxylomannan Epitope That Elicits Protective Antibodies

Wendy Cleare,1 Robert Cherniak,2 and Arturo Casadevall1,3,*

Department of Microbiology and Immunology1 and Department of Medicine, Division of Infectious Diseases,3 Albert Einstein College of Medicine, Bronx, New York 10461, and Laboratory for Biological and Chemical Sciences, Department of Chemistry, Georgia State University, Atlanta, Georgia 303032

Received 16 November 1998/Returned for modification 11 January 1999/Accepted 15 March 1999

The monoclonal antibody (MAb) 2H1 defines an epitope in Cryptococcus neoformans capsular glucuronoxylomannan (GXM) that can elicit protective antibodies. In murine models of cryptococcosis, MAb 2H1 administration prolongs survival and reduces fungal burden but seldom clears the infection. The mechanism by which C. neoformans persists and escape antibody-mediated clearance is not understood. One possibility is that variants that do not bind MAb 2H1 emerge in the course of infection. Using an agglutination-sedimentation protocol, we recovered a variant of strain 24067 that did not agglutinate, could not be serotyped, and had marked reduction in GXM O-acetyl groups. Binding of MAb 2H1 to 24067 variant cells produced a different immunofluorescence pattern and lower fluorescence intensity relative to the parent 24067 cells. Addition of MAb 2H1 to 24067 variant cells had no effect on cell charge. Phagocytic assays demonstrated that MAb 2H1 was not an effective opsonin for the 24067 variant. The 24067 variant was less virulent than the 24067 parent strain in mice, and MAb 2H1 administration did not prolong survival in animals infected with the variant strain. To investigate whether variants which do not bind MAb 2H1 are selected in experimental infection, three C. neoformans strains were serially passaged in mice given either MAb 2H1 or no antibody. Analysis of passaged isolates by agglutination assay, flow cytometry, and indirect immunofluorescence revealed changes in MAb 2H1 epitope expression but no clear trend with regards to gain or loss of MAb 2H1 epitope. C. neoformans variants with reduced MAb 2H1 epitope content can be isolated in vitro, but persistence of infection in mice given MAb 2H1 does not appear to be a result of selection of escape variants that lack the MAb 2H1 epitope.

* Corresponding author. Mailing address: 1300 Morris Park Ave., Golding 701, Bronx, NY 10461. Phone: (718) 430-4259. Fax: (718) 430-8968. E-mail: casadeva{at}aecom.yu.edu.

Infection and Immunity, June 1999, p. 3096-3107, Vol. 67, No. 6
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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