Following infection with 103 cells of Cryptococcus neoformans, progressive multiplication occurred in all tissues for 7 to 28 days. Thereafter, most mice gained control of the infection so that 3 to 6 months after inoculation, tissues were usually sterile or contained only small numbers of cryptococci. Survivors challenged 1 to 4 months after infection with 103 cells lived longer than controls and had an increased survival rate. Pretreatment with bacterial endotoxin also resulted in protection against cryptococcal challenge. Endotoxin-protected animals showed no ability to limit the infection until circulating antibody could be demonstrated.
Histologic studies revealed an increased cellular infiltration in the brains of specifically protected and endotoxin-protected mice 1 to 2 weeks after challenge. However, control of cryptococcal multiplication could be correlated with the presence of antibody but could not be correlated with the enhanced cellular response.
Although protection against cryptococcal challenge appears to be antibody-dependent, it is unclear whether protective antibody is to be found in plasma or is tissue-bound.