Microbiology (1 9961, 142,927-935 Printed in Great Britain 1 Laboratoire de Pharmacologie et de Toxico logie Fondamentales du CNRS and Universite Paul Sabatier, 118 route de Narbonne, 31 062 Toulouse Cedex, France 2 Mycobacteria Department, Statens Seruminstitut, 5 Artillerivej, DK-2300 Copenhagen 5, Denmark The outermost capsular arabinomannans and other mannoconjugates of virulent and avirulent tubercle bacilli Annick Ortalo-Magne,’ Ase B. Andersen’ and Mamadou Daffel Author for correspondence: Mainadou Daffi. Tel: +33 61 33 59 16. Fax: +33 61 33 58 86. e-mail: daffe@lptf.biotoul.fr It has been shown that phagocyte mannose receptors play an important role in phagocytosis of virulent tubercle bacilli, but not of avirulent strains. Accordingly, we investigated the occurrence and structure of the outermost mannoconjugates of the capsule of five strains of the tubercle bacillus differing in their degrees of virulence. The extracellular and surface-exposed arabinomannan-containing polysaccharides were chemically characterized as being composed mainly of neutral fatty-acyl-free arabinomannans (AMs) possessing a reducing end consisting of mannose. Although no lipoarabinomannan (LAM) was detected, small amounts of acidic polysaccharides, exhibiting the same electrophoretic mobility as LAM, were identified as succinylated AMs (two to three residues per molecule) lacking the phosphatidylinositol anchor of LAM. AMs from the different strains shared the same structural features, notably the capping of a large portion of the arabinan segments with mannosyl residues. However, no correlation was observed between either the percentage of capping or the amount of AMs and the degrees of virulence of the strains. The occurrence and amounts of other mannoconjugates (phosphatidylinositol mannosides and the mannose- associated 19 and 38 kDa lipoproteins) in the various tubercle bacilli were also examined. Although both classes of compounds were identified in all the examined strains, a correlation between the amounts of the glycoconjugates and the degrees of virulence of the strains could not be established. These data do not support the implication of these promising mannosylated molecules in the selective phagocytosis of virulent tubercle bacilli and indicate that the involvement of mannose receptors in phagocytosis of virulent M. tuberculosis needs to be re-investigated. Keywords : tuberculosis, Mycobacterizm, glycoconjugates, arabinomannan, capsule INTRODUCTION Tuberculosis remains a major health problem, claiming three million lives annually. The World Health Organi- zation estimates that one-third of the world’s population is, or has been, infected with the tubercle bacillus and is at risk of developing the disease (Kochi, 1991). The steadily declining incidence of tuberculosis in industrialized coun- tries over several decades has been reversed due to the Abbreviations: AMs, arabinomannans; LAMS, lipoarabinomannans; LMs, lipomannans; ManAMs, mannose-capped arabinomannans; ManLAMs, mannose-cappedlipoarabinomannans; PIMs, phosphatidylinositol manno- sides. emergence of drug-resistant strains and the coincidence of tuberculosis and HIV infection (Bloom & Murray, 1992). Mycobacteritrm ttrberctrlosis, the causative agent of tubercu- losis, is a facultative intracellular pathogen capable of resisting destruction and multiplying inside mononuclear phagocytic cells. Little is known, however, about the mechanisms of its pathogenicity. The initial step in the host entry by the bacillus is phagocytosis. It has been shown that complement receptors CR1, CR3 and CR4 are involved in the phagocytosis of mycobacteria, including M . ttrberctrlosis (Bermudez et al., 1991 ; Hetland & Wiker, 1994 ; Hirsch et al., 1994 ; Schlesinger, 1993 ; Schlesinger & Horwitz, 1990, 1991 ; Schlesinger et al., 1990; Stokes et al., 1993). In addition to these receptors, the mannose 927 0002-0358 0 1996 SGM