Cryptococcus neoformans recovered from the cerebrospinal fluid (CSF) of eight patients, seven with the acquired immunodeficiency syndrome (AIDS) or AIDS-related complex (ARC), were studied to assess the relationship between degree of encapsulation noted in fresh CSF with that observed after animal passage. We further correlated encapsulation with extent of immunodeficiency in these patients. Results of these studies showed poor encapsulation (mean capsule plus cell diameter less than 10 μm) in six patients, intermediate in one (mean 15.5μm), and full encapsulation in one (mean 24.4 μm). The last isolate was observed in the CSF from the only patient without convincing clinical evidence for AIDS. Mouse passage of cryptococci from 5 AIDS patients and one with ARC resulted in a statistically significant (P<0.05) increase in capsule size over that observed directly in fresh cerebrospinal fluid. Cryptococci derived from the non-AIDS patient did not show an increase in encapsulation after mouse passage. These studies suggest that the immune deficiency state associated with AIDS exerts little selective pressure on inhaled poorly encapsulated C. neoformans.
