Enzyme immunoassay detection of IgM to galactoxylomannan of Cryptococcus neoformans

Abstract

Antibodies against the major capsular polysaccharide of Cryptococcus neoformans, glucuronoxylomannan (GXM), and a minor secreted polysaccharide, galactoxylomannan (GalXM), were surveyed by indirect enzyme immunoassay (EIA) in patients with cryptococcosis, with other mycoses, and in normal controls. Measurement of IgG levels against GalXM revealed cross reactions in candidiasis patients that were reduced by adsorption with Candida albicans cell walls. Measurement of IgM levels were subject to fewer cross reactions. The combination of adsorption with C albicans cell walls and measurement of IgM detected antibodies in 12 of 55 cryptococcosis patients. An end point equal to or greater than a titer of 1/16 excluded reactions in normals and limited cross reactivity in candidiasis patients to below 7%. This test has potential diagnostic significance in cryptococcosis patients who show no evidence of cryptococcal antigen circulating in the cerebrospinal fluid or serum. Reactions in this IgM assay were not spuriously due to rheumatoid factor. The major capsular GXM was much less serologically active and was subject to cross reactions with agents of bacterial sepsis. The specificity of the GalXM is directed mainly by the mannose and to a lesser extent by galactosyl residues.