Antibody response to Cryptococcus neoformans proteins in rodents and humans

Abstract

The prevalence and specificity of serum antibodies to Cryptococcus neoformans proteins was studied in mice and rats with experimental infection, in individuals with or without a history of potential laboratory exposure to C. neoformans, human immunodeficiency virus (HIV)-positive individuals who developed cryptococcosis, in matched samples from HIV-positive individuals who did not develop cryptococcosis, and in HIV-negative individuals. Rodents had little or no serum antibody reactive with C. neoformans proteins prior to infection. The intensity and specificity of the rodent antibody response were dependent on the species, the mouse strain, and the viability of the inoculum. All humans had serum antibodies reactive with C. neoformans proteins regardless of the potential exposure, the HIV infection status, or the subsequent development of cryptococcosis. Our results indicate (i) a high prevalence of antibodies reactive with C. neoformans proteins in the sera of rodents after cryptococcal infection and in humans with or without HIV infection; (ii) qualitative and quantitative differences in the antibody profiles of HIV-positive individuals; and (iii) similarities and differences between humans, mice, and rats with respect to the specificity of the antibodies reactive with C. neoformans proteins. The results are consistent with the view that C. neoformans infections are common in human populations, and the results have implications for the development of vaccination strategies against cryptococcosis.

FIG. 1

Immunoblots showing the reactivity of sera from A/JCr mice inoculated with either live or dead cells of C. neoformans 24067 with whole protein extracts from cryptococcal cells. Proteins were separated electrophoretically by SDS–7.5% polyacrylamide gel electrophoresis (PAGE). The treatment of the cells is indicated above the lanes, and the molecular mass standards are shown on the left in kilodaltons. Each lane contains sera from a different mouse. The dye front runs ahead of the 25.4-kDa marker.

FIG. 2

Immunoblots showing the reactivity of sera from A/JCr mice with whole protein extracts from cryptococcal cells after infection with a single or with multiple C. neoformans strains. Proteins were electrophoresed by SDS–10% PAGE. Labels above the lanes indicate the strain combination used to infect the mice. The PBS group represents mice given PBS i.t. Each lane contains sera from a different mouse.

FIG. 3

Immunoblots showing the reactivity of sera from five mouse strains with whole protein extracts from cryptococcal cells after infection with strain 24067 at day 35 of infection. Each panel shows three lanes corresponding to three individual mice. Protein extracts were electrophoresed by SDS–10% PAGE and transferred to nitrocellulose.

FIG. 4

Immunoblots showing the reactivity of sera from seven human subjects with cytosolic proteins from strain 24067 by separated by SDS–7.5% PAGE. Numbers above the lanes indicate the serum sample. All serum samples except sample 1 were used at a dilution of 1:250. Sample 1 is shown here at a dilution of 1:100. Molecular masses are indicated on the left in kilodaltons. The 25.4-kDa marker is just above the dye front.