Ch. Mody et al., PROTEINS IN THE CELL-WALL AND MEMBRANE OF CRYPTOCOCCUS-NEOFORMANS STIMULATE LYMPHOCYTES FROM BOTH ADULTS AND FETAL CORD-BLOOD TO PROLIFERATE, Infection and immunity, 64(11), 1996, pp. 4811-4819
Cryptococcus neoformans is an encapsulated yeast that infects patients
who have defective cell-mediated immunity, including AIDS, but rarely
infects individuals who have intact cell-mediated immunity. Studies o
f the immune response to C. neoformans have been hampered by a paucity
of defined T-lymphocyte antigens, and hence, the understanding of the
T-cell response is incomplete. The goal of this study was to separate
C. neoformans into its component parts, determine whether those compo
nents stimulate lymphocyte proliferation, perform preliminary characte
rization of the proteins, and establish the potential mechanism of lym
phocyte proliferation, The lymphocyte response to fungal culture mediu
m, whole organisms, disrupted organisms, and the yeast intracellular f
raction or cell wall and membrane was studied by determining thymidine
incorporation and by determining the number of lymphocytes at various
times after stimulation, The cell wall and membrane of C. neoformans
stimulated lymphocyte proliferation, while the intracellular fraction
and culture filtrate did not, The optimal response occurred on day 7 o
f incubation, with 4 x 10(5) peripheral blood mononuclear cells per we
ll and with 13 mu g of cryptococcal protein per ml. The number of lymp
hocytes increased with time in culture, indicating that thymidine inco
rporation was accompanied by proliferation, Proteinase K treatment of
the cell wall and membrane abrogated lymphocyte proliferation, indicat
ing that the molecule was a protein. [S-35]methionine labeling, sodium
dodecyl sulfate-polyacrylamide gel electrophoresis, and fluorography
were performed to analyze the proteins contained in the cell wall and
membrane, intracellular fraction, and culture filtrate, At least 18 di
screte bands were resolved from the cell wall and membrane. Since a la
rge percentage of healthy adults responded to the cryptococcal cell wa
ll and membrane, a mitogenic effect was investigated by testing prolif
eration of fetal cord blood lymphocytes, The percentage of fetal sampl
es that proliferated in response to the cell wall and membrane was sim
ilar to the percentage of fetal samples that proliferated in response
to Staphylococcus enterotoxin B, a microbial mitogen. Thus, a protein
in the cell wall and membrane of C, neoformans is a potent stimulant o
f lymphocyte proliferation and has mitogenic properties, which may hav
e important implications for cell-mediated immunity to C. neoformans.