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Infection and Immunity, February 1999, p. 936-941, Vol. 67, No. 2
Department of Microbiology and Infectious
Diseases1 and
Department of Internal
Medicine,2 University of Calgary, Calgary,
Alberta, Canada T2N 4N1
Received 16 July 1998/Returned for modification 18 August
1998/Accepted 21 October 1998
The mechanism of human T-lymphocyte activation by the pathogenic
yeast Cryptococcus neoformans has not been established.
Previous investigations have suggested that C. neoformans
contains a mitogen for T lymphocytes, while other investigators have
attributed lymphocyte proliferation in vitro to a recall antigen.
Because of the potential importance of the mechanism of T-cell
activation for our understanding of the immune response to
C. neoformans, the present studies were performed to
determine whether C. neoformans contains a mitogen for T
lymphocytes. C. neoformans stimulates fetal blood
lymphocytes to proliferate and stimulates proliferation of
CD45RA+ cells from adults, indicating that it stimulates
naive T cells. The T-cell response to C. neoformans was
dependent upon the presence of accessory cells. However, allogeneic
cells were sufficient for accessory cell function, indicating that the
response was not major histocompatibility complex restricted. The
percentage of T cells in the cell cycle was higher than that with the
recall antigen tetanus toxoid but lower than that with the mitogenic lectin phytohemagglutinin A or the superantigen
Staphylococcus enterotoxin B. Precursor frequency analysis
established that 1 in 7,750 ± 2,270 T cells proliferated in
response to the cryptococcal cell wall and membrane. Compared
to the case for most mitogens or superantigens, the proliferative
response is late and the number of T cells that enter the cell cycle
and the precursor frequency are low, indicating that the mitogenic
effect is modest. However, the mitogenic effect of C. neoformans should be considered when interpreting the immune
response to C. neoformans, since even weak mitogens can
have profound effects on host defense.
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
The Cell Wall and Membrane of Cryptococcus
neoformans Possess a Mitogen for Human T Lymphocytes
*
Corresponding author. Mailing address: Division of
Pulmonary Medicine, Room 273, Heritage Medical Research Building,
University of Calgary, Calgary, Alberta, Canada T2N 4N1. Phone: (403)
220-8479. Fax: (403) 270-8928. E-mail:
cmody{at}acs.ucalgary.ca.
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