Serologic evidence for reactivation of cryptococcosis in solid-organ transplant recipients

Abstract

Cryptococcosis is a significant infection with a high mortality in solid-organ transplant recipients. Nonetheless, the pathogenesis of this disease is poorly understood. It has been hypothesized that cryptococcosis may result from either primary infection or reactivation of a latent infection. Sera were obtained from transplant recipients prior to transplantation and at the time they developed cryptococcosis. Control sera were obtained before and after transplant from patients who did not develop cryptococcosis. Sera were tested for antibodies against Cryptococcus neoformans by using an immunoblot assay. Antibody responses were also compared with those observed in sera from rats with experimental pulmonary cryptococcosis. In all, 52% of the transplant recipients who developed cryptococcosis exhibited serologic evidence of cryptococcal infection before transplantation. These patients developed cryptococcosis significantly earlier after transplant than patients without preexisting reactivity did (5.6 +/- 3.4 months compared to 40.6 +/- 63.8 months, respectively [P = 0.0011]). The results from our study suggest that a substantial proportion of transplant-associated cryptococcosis cases result from the reactivation of a latent infection. These findings also highlight the potential utility of serologic studies in identifying patients at risk for the development of cryptococcosis after transplantation.

FIG. 1.

Immunoblots for rats infected intratracheally with Cryptococcus neoformans. Representative sera from rats at different times following infection are shown. Rats with resolved infection were inoculated intratracheally with an acapsular strain of C. neoformans and demonstrated to have no lung fungal burden. Some rats (10MOS/DEXA) were infected with C. neoformans for 9 months and then treated with dexamethasone for a month. The top and bottom panels show blots obtained with whole-cell protein and cytoplasmic extracts of C. neoformans, respectively. Molecular mass markers in kDa are shown on the right.

FIG. 2.

(A) Median numbers of total cytoplasmic proteins recognized by sera from Pre/− (n = 11), Pre/+ (n = 21), Post/+ (n = 21), and Post/− (n = 10) patients (P value was not significant). Panel B shows median numbers of designated cytoplasmic proteins recognized by sera from the same patients. (the asterisk indicates a P value of <0.01 for Post/+ sera compared to Post/− sera and for Post/+ sera versus Pre/− sera). Bars represent one standard deviation each.

FIG. 3.

(A) Representative immunoblots of paired sera from 10 transplant recipients that developed cryptococcosis. For each pair, blots on the left were made with sera obtained prior to transplant, while blots on right were made with sera obtained after transplant at the time that the diagnosis of cryptococcosis was made. (B) The corresponding median numbers of designated proteins recognized by these paired sera are shown.

FIG. 4.

Proportions of sera demonstrating reactivity to designated cytoplasmic proteins among the various cohorts. White fills represent minimal reactivity (0 to 2 bands), black fills represent moderate reactivity (3 to 5 bands), and gray fills represent extensive reactivity (≥6 bands).