from the bacterial wall into the surroundings. Consequently, the O-polysaccharide often dictates the immunodeterminant behaviour of the organism, and it differs for each type within a species. Most wild-type bacteria carry O-polysaccharide and are then said to be in the smooth- or S-form. Bacteria not carrying O-polysaccharide, but only possessing the lipid A/core combination are said to be of the rough- or R-form. These terms are descriptive of their respective colony morphology. The presence of O-polysaccharide cannot be regarded as a necessary factor for pathogenicity, since R-type LPS is observed in some wild-type bacteria that are highly pathogenic in humans (e.g. Bordetella pertussis, Neisseria gonorrhoeae, and others). Below are two examples of an LPS. The first is for Salmonella, the second for Legionella pneumophila. Note that although the core regions are quite different, both are short saccharidic stretches situated between the lipid A and the O-chain. Note also that KDO is the sugar residue linked to the lipid A portion (VI):

where GlcNAc = N-acetyl D-glucosamine, Gal = galactose, Hep = Heptose, KDO = keto-deoxy-octulo-sonic acid, EtAm = 2-aminoethyl, P = phosphate, FE = fatty acid ester. The lipid A is indicated on the right, while the O-polysaccharide is indicated on the left. The location of the phosphates or 2-amino-phosphates, or the branch-terminating KDO, remains tentative (VII).

In the case of systemic infection by gram-negative organisms, the overwhelming amount of solubilized endotoxin produced by bacterial lysis can cause shock and even death. It is interesting to note that affinity-purified rabbit anti-LPS immunoglobulin M (IgM) and IgG protects rats lethally challenged with Pseudomonas aeruginosa.

Concerning (2), in addition to the polysaccharide antigens, such as discussed above, many mammalian or viral cell walls carry glycoproteins and/or glycolip-ids on or in them, and these can define their antigenicity. Glycoproteins are proteins that are naturally substituted by short and/or medium length

P EtAm-P-P

(0-PS)(1 - 4)-<x-o-Glc(1 —2)-a-D-Gal(1 ~3)-a-d-Glc(1 -3)-a-Hep(1 -3)-a-Hep(1 -5)-a-KDO-LipldA 2 6 7 4

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