Pathophysiology
Clinical meaning
Cryptococcus neoformans is an encapsulated yeast acquired through inhalation of spores from contaminated soil (particularly pigeon droppings). The polysaccharide capsule is the primary virulence factor, inhibiting phagocytosis and suppressing T-cell responses. In immunocompetent hosts, cell-mediated immunity typically contains the infection as granulomas. In immunocompromised patients (especially those with CD4 counts < 200 cells/mcL), the organism proliferates unchecked in alveolar macrophages, causing pneumonia with a propensity for hematogenous dissemination to the central nervous system (cryptococcal meningitis).