Significance of antibody detection in the diagnosis of cryptococcal meningitis

Cryptococcus neoformans is the causative agent of Cryptococcosis, a chronic and life-threatening infection common in AIDS patients. Sonicated proteins of cryptococci were reported to contain antigenic properties. In the present study antigens are prepared from cryptococcal culture filtrate and by sonication. Secretory antigens are prepared by precipitation of culture filtrate using saturated ammonium sulfate followed by dialysis. Prepared antigens are tested for the presence of antibodies in the CSF samples of cryptococcal meningitis cases by ELISA. Comparison is made between India ink staining, latex antigen test, and the antibodies to the sonicated and secretory antigens. The results indicate that although antigen could be detected in the majority of samples, antibody could also be detected to the extent of 80-85%. It is interesting to note that some samples that were negative for India ink staining also showed high antibody responses. Hence, antibody detection could be a valuable marker in association with India ink staining for the early diagnosis of the cryptococcal infection. This test may also counter false positivity encountered in latex antigen test. Antibody detection assay would be a viable alternative, which has 83% sensitivity and 100% specificity. Thus the presently described test aids in immunodiagnosis of cryptococcal infection.