The Virulence-enhancing Factor of Mucins

In preceding papers of this series (Smith, 1950a, b, 1951a; Smith, Harris-Smith & Stanley, 1951) the virulence-enhancing action of mucin has been shown to be a synergic combination of a viscous medium, a particulate residue Iand a more specific 'third factor'. The activity of the latter, in a biological assay in which the other two factors were kept constant (Smith et al. 1951), was shown to reside in the carbohydrate moiety (Smith, Gallop & Stanley, 1952) which has been separated into several components. Polysaccharide A, the most active component, was purified and identified as a heparin (Smith, Gallop, Harris-Smith & Stanley, 1952). Impure polysaccharide B, a sulphated compound, had a low activity, a proportion of which could be attributed to contamination with polysaccharide A. The latter has now been removed (see preceding paper); as was expected the activity of polysaccharide B (see below) then dropped to a value which ruled out this polysaccharide as a significant participant in the virulence enhancement. Polysaccharide C, also impure, was a fairly active neutral polysaccharide, and formed a synergic combination with polysaccharide A in the biological assay (Smith, Gallop & Stanley, 1952). The preceding 'paper described the discovery and purification of a further polysaccharide, polysaccharide D; it has a significant virulence-enhancing activity (see below) similar to that of polysaccharide C. This paper deals mainly with the identification of polysaccharide C as the blood-group mucoid ofboth A and H activity, which has been previously isolated by Morgan & King (1943) and Bendich, Kabat & Bezer (1946). Proof is also provided that the virulence-enhancing activity in the biological assay for the third factor is not specifically connected with either blood-group A or H activity (see also Smith, 1950a). In addition, as befits the concluding paper of the series, various observations are made on the virulence-enhancing action of whole 'mucin', now that the chief factors operating in this complex system have been identified.