FIG. 4.

Acquired immunity to C. neoformans in young adult and aged mice. Female B6D2F₁ young adult and aged mice were vaccinated by intratracheal instillation of 10⁶ strain 184 yeast cells. After 10 weeks, five young adult mice and four aged mice, along with age-matched naive controls, received 2 × 10⁴ yeast cells intravenously. Mice were killed at 10 days of infection, and yeast cells were enumerated in brains and lungs. Data are the means ± standard deviations for five mice except for aged, vaccinated mice (n = 4). Differences in yeast burdens between naive and immune brains and lungs are significant (P < 0.05) both for the young adult and aged mice.