Induced sensitization of normal laboratory animals to Brucella abortus endotoxin

Chemical characterization and biological properties of lipopolysaccharides isolated from smooth and rough strains of Brucella abortus

The chemical composition and some of the biological activities of lipopolysaccharides (LPS) extracted from a smooth-intermediate strain (45/0) and a rough strain (45/20) of Brucella abortus have been examined. LPS were found in both the phenolic and aqueous extraction phases of strain 45/0, but only in the aqueous phase of 45/20. The phenolic LPS contained 9- to 16-fold-lower levels of heptose and reduced amounts of dideoxyaldoses compared with aqueous fractions. The major neutral sugars were glucose, galactose, and mannose. beta-Hydroxymyristic-acid, a common marker of enteric LPS, was not detected. Fatty acids present in highest amounts were hydroxylated and nonhydroxylated species with chain lengths of 16, 18, and 20 carbons. Only the phenolic LPS of strain 45/0 exhibited mouse lethality and a curable wasting disease; however, both phenolic and aqueous fractions caused carbohydrate depletion in mice. The toxicity of aqueous LPS could not be potentiated with Pb(OAc)4. These data, coupled with the lack of mitogenic activity for B-lymphocytes, are indicative of the unique structure-function relationships of Brucella LPS.

Lipid A-induced tolerance and hyperreactivity to hypothermia in mice

Mice responded to lipopolysaccharide (LPS) with a dose-dependent, monophasic hypothermia reaching a maximum at 2 h postinjection. Degraded polysaccharide was not active; free lipid A, however, induced a similar pattern of hypothermia, indicating that the hypothermic principle of LPS was embedded within the lipid A component. The hypothermic response of mice to LPS was modified by prior exposure of the host to LPS. This altered reactivity was manifested by refractory periods (early and late tolerance), in which animals no longer responded with hypothermia, or a hyperreactive phase (hypersensitivity), in which hypothermic responses were greatly augmented upon LPS challenge. Thus, tolerance observed 24 h after a single injection of LPS (early tolerance) was followed, on further LPS challenge, by an enhanced hypothermic responses reaching a maximum on day 4. Further daily exposure of the animals to LPS eliminated hyperreactivity and led to the establishment of a late tolerance maximally expressed on day 8. Hyperreactivity could also be evoked on day 4 after a single injection of LPS. Mice pretreated with Salmonella S- and R-form LPS or free lipid A (Salmonella) demonstrated tolerance and hyperreactivity to both homologous and heterologous challenge. In addition, complete cross-tolerance was observed with S-form LPS derived from Shigella. It was concluded that the differential effects of LPS on host responses (tolerance and hyperreactivity) were due to lipid A.

Inhibition by oxisuran of cell-mediated hypersensitivity by decrease in numbers of specifically sensitized cells

Oxisuran, 2-([methylsulfinyl]acetyl)pyridine, has previously been shown to selectively suppress cell-mediated immunity, as measured by prolongation of allograft survival, without inhibition of humoral immunity. In the present investigation, the influence of this compound on lymphoid cell transfer of delayed hypersensitivity was studied. In actively sensitized animals, including endotoxin-sensitized mice and rabbits, ovalbumin-, dinitrochlorobenzene-, and dinitrofluorobenzene-sensitive guinea pigs, or tuberculin-sensitive rats, daily treatment during the interval just preceding the elicitation and expression of the hypersensitivity was most inhibitory. In both endotoxin-sensitive mice and ovalbumin-sensitive guinea pigs, treatment of the sensitized cell donor just prior to lymphoid cell harvest and transfer resulted in inhibition of the expression of the hypersensitivity in untreated recipients. Approximately 10(4) fewer specifically sensitized lymphoid cells, but not fewer viable cells, were present in passively transferred cell preparations. In contrast, treatment of the lymphoid cell recipient in the same experimental model did not influence the expression of the transferred hypersensitivity. The results suggest that oxisuran may influence an as yet undefined event prior to the expression of a cell-mediated hypersensitivity response in sensitized animals.

The immunization of guinea-pigs and mice with a whole-culture extract of a smooth and a rough strain of Brucella abortus

A purified killed Br. abortus vaccine developed for use in man from the smooth strain 544 and previously tested in mice (Keppie, Witt and Smith, 1971) has now been shown to immunize guinea-pigs without the addition of adjuvant. A similar vaccine prepared from the rough strain 45/20 also immunized guinea-pigs but to a slightly lesser degree. The activity of both vaccines in the guinea-pig was markedly enhanced by the use of water-in-oil emulsions. A commercially available killed vaccine, “Duphavac”, prepared from strain 45/20 for use in cattle, was slightly more active in guinea-pigs than the emulsified whole-culture extract of “544” possibly because its oily adjuvant was different. In mice, all the “45/20” vaccines were only feebly protective even when given with oily adjuvant, in sharp contrast to the “544” vaccines which were highly active in this animal, with or without adjuvant.

As expected, the “45/20” vaccines were much less agglutinogenic than the “544” vaccines but both produced a similar degree of delayed hypersensitivity in guinea-pigs.

It is suggested that the whole-extract vaccine from strain 544 is suitable for a trial in man.