The adsorption of bacterial polysaccharides by erythrocytes.

Bacterial lipopolysaccharides and O' somatic antigens usually require treatment with alkali for maximal adsorption on erythrocytes in preparation for indirect haemagglutination. Although heating enhances sensitizing activity, owing partly to increasing dispersion, it is always less effective than alkali treatment. The presence of a protein component or of the chloroform soluble lipid A' does not inhibit erythrocyte sensitizing activity and no change in sugar constituents has been detected as a result of treatment. The specific polysaccharide of , which contains no lipid, requires alkali treatment for activity; in this case the effect of alkali is to remove -acetate (4 per cent). The loss of weight on treatment is also 4 per cent and no other differences can be detected by examining the infrared-absorption spectra of treated and untreated samples. For other materials investigated a loss of -acetyl has been detected, except where alkali treatment is not required to elicit maximal activity, e.g. the lipopolysaccharide which contains about 50 per cent of lipid `A'. By reacetylation of alkali treated polysaccharides it has been shown that -acetyl residues inhibit adsorption on to erythrocytes, but in some instances higher fatty acids are also removed to some extent by treatment with alkali.