Cryptococcus neoformans, an opportunistic fungal pathogen ubiquitously present in the
environment, causes cryptococcal meningitis (CM) mainly in immunocompromised
patients, such as AIDS patients. We aimed to identify disease-associated cryptococcal
protein antigens targeted by the human humoral immune response. Therefore, we used
sera from Colombian CM patients, with or without HIV infection, and from healthy
individuals living in the same region. Serological analysis revealed increased titers of
anti-cryptococcal IgG in HIV-negative CM patients, but not HIV-positive CM patients,
compared to healthy controls. In contrast, titers of anti-cryptococcal IgM were not affected
by CM. Furthermore, we detected pre-existing IgG and IgM antibodies even in sera from
healthy individuals. The observed induction of anti-cryptococcal IgG but not IgM during
CM was supported by analysis of sera from C. neoformans-infected mice. Stronger
increase in IgG was found in wild type mice with high lung fungal burden compared to
IL-4Ra-deficient mice showing low lung fungal burden. To identify the proteins targeted by
human anti-cryptococcal IgG antibodies, we applied a quantitative 2D immunoproteome
approach identifying cryptococcal protein spots preferentially recognized by sera from CM
patients or healthy individuals followed by mass spectrometry analysis. Twenty-three
cryptococcal proteins were recombinantly expressed and confirmed to be
immunoreactive with human sera. Fourteen of them were newly described as
immunoreactive proteins. Twelve proteins were classified as disease-associated
antigens, based on significantly stronger immunoreactivity with sera from CM patients
compared to healthy individuals. The proteins identified in our screen significantly expand
the pool of cryptococcal proteins with potential for (i) development of novel anticryptococcal
agents based on implications in cryptococcal virulence or survival, or
(ii) development of an anti-cryptococcal vaccine, as several candidates lack homology
to human proteins and are localized extracellularly. Furthermore, this study defines preexisting
anti-cryptococcal immunoreactivity in healthy individuals at a molecular level,
identifying target antigens recognized by sera from healthy control persons
