Mtb is a Gram-positive encapsulated organism and its capsule is composed of lipid derivatives of arabinomann (AM) and glucan (Glu). The role of these CPs in pathogenesis of and immunity to Mtb is unknown;however, capsular polysaccharides (CPs) of other pathogenic bacteria such as Haemophilus influenzae type b, Streptococcus pneumonia, Neisseria meningitidis and Salmonella typhi have been shown to inhibit the uptake of bacteria by leukocytes, thereby preventing initial control of infection. Antibody to these CPs promote clearance of the organisms. Because the CPs of these bacteria are used for diagnosis and prevention of diseases caused by these pathogens, we evaluated the Mtb CPs as potential diagnostic reagents and vaccines for TB. This pilot study assessed antibody responses to the two CPs of Mtb among immunocompetent persons stratified according to their history of infection with and/or disease caused by Mtb. Serum antibody levels against the two surface CPs were shown to be higher among subjects with active or treated tuberculosis. Similar results showing higher AM IgG antibody levels in TB patients than in controls, and higher in TB-HIV negative than in TB-HIV positive patients, were published recently. Our data provide quantitative evidence that disease caused by Mtb elicits an immune response to the CPs. The small sample sizes in our study may have interfered with the ability to detect significant differences among groups for several isotypes of antibody. Expanded studies of defined populations are indicated in order to assess the utility of these assays for epidemiologic and/or clinical purposes.
