Abstract
We defined optimal conditions for detection of cryptococcal antigen using latex particles sensitized with anti-C. neoformans globulin fractionated by 40 % saturated ammonium sulfate. Latex particles, with a diameter of 0.81 μm, were sensitized with 20 μg of anti-C. neoformans globulin per mg latex. The agglutination test was performed using a mixture of 75 μl of protease treated serum or cerebrospinal fluid (CSF) and 25 μl of sensitized latex suspension. After 10 minutes reaction on a rotator, the agglutination was read. We compared the minimal concentration of polysaccharide antigen detectable with our materials and procedure and with commercially available kits and obtained almost the same sensitivities. However, our procedure was also capable of detecting antigen in soluble immune complexes in patient's serum. The sensitivity of our latex agglutination test using the sensitized latex particles was found to be 100% in cases of cryptococcal meningitis, 81.8% in pulmonary cryptococcosis and 75 % in cutaneous cryptococcosis. The specificity of our test was 100% with sera and 95% with CSF. We concluded that commercial kit B was the more useful because of its protease pre-treatment which reduced the problems of false positives due to rheumatoid factor and false negatives due to soluble immune complexes.
