THE OUTERMOST CAPSULAR ARABINOMANNANS AND OTHER MANNOCONJUGATES OF VIRULENT AND AVIRULENT TUBERCLE-BACILLI

It has been shown that phagocyte mannose receptors play an important r ole 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 t ubercle bacillus differing in their degrees of virulence. The extracel lular and surface-exposed arabinomannan-containing polysaccharides wer e chemically characterized as being composed mainly of neutral fatty-a cyl-free arabinomannans (AMs) possessing a reducing end consisting of mannose. Although no lipoarabinomannan (LAM) was detected, small amoun ts of acidic polysaccharides, exhibiting the same electrophoretic mobi lity as LAM, were identified as succinylated AMs (two to three residue s per molecule) lacking the phosphatidylinositol anchor of LAM, AMs fr om 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 perc entage of capping or the amount of AMs and the degrees of virulence of the strains, The occurrence and amounts of other mannoconjugates (pho sphatidylinasitol mannosides and the mannose-associated 19 and 38 kDa lipoproteins) in the various tubercle bacilli were also examined. Alth ough both classes of compounds were identified in all the examined str ains, a correlation between the amounts of the glycoconjugates and the degrees of virulence of the strains could not be established. These d ata do not support the implication of these promising mannosylated mol ecules in the selective phagocytosis of virulent tubercle bacilli and indicate that the involvement of mannose receptors in phagocytosis of virulent nn. tuberculosis needs to be re-investigated.