Reactivation of a residual Brucella abortus 19 vaccine infection in mice by a virulent challenge or by injection of brucellin or of Brucella lipopolysaccharide.

Facultative intracellular bacteria localize preferentially in reticulo endothelial system organs where they can either multiply or be destroyed, concomitantly or successively. Immunity may thus be estimated by counts of viable (surviving) bacteria at convenient time(s) after a standard challenge. When mice vaccinated with the living attenuated Brucella abortus strain 19 were intravenously challenged with the virulent B abortus strain 544, some mice exhibited unexpected high spleen counts. The vaccinal strain surviving at low level in some mice 30 days after a subcutaneous vaccination was reactivated by the virulent challenge as evidenced by a fast but temporary count increase. Reactivation was stronger in outbred OF 1 mice than in outbred CD-1 mice. Reactivation did not alter the normal course of the virulent infection as shown by comparison between mice already cured of the vaccinal infection or not, at time of challenge. Because reactivation was also induced by intravenous injection of either the brucellin allergen or the brucella lipopolysaccharide antigen, hypersensitivity reactions occurring inside the vaccinal granuloma foci may expel the surviving bacteria into the surrounding extracellular environment where a secondary growth may develop.

[Anti-Brucella immunity transferred by immune serum and that transferred by splenic lymphocytes cannot be added]. / L'immunité anti-Brucella transférée par sérum immun et l'immunité transférée par les lymphocytes spléniques ne s'additionnent pas.

Immune serum and spleen cells from mice vaccinated with a cell-wall fraction (PG) from Brucella were previously shown to transfer a good protection to mice against a virulent Brucella challenge. This protection estimated by spleen and liver time-course infection was similar to that afforded by vaccination. In present experiments, DBA/2 mice were first transferred with either immune serum from infected mice, splenic cells from mice intravenously vaccinated with PG fraction 28 days previously, or both immune serum and splenic cells. In this case, the serum was either injected before the challenge, as were the splenic cells, or 2 days after it in order to reduce the lowering effect of the serum on level of initial colonization of the spleen. The transferred mice were then intravenously challenged with the virulent strain B. abortus 544 and liver and spleen counts were performed on groups of five mice weekly up to six weeks. Immune serum and splenic cells from vaccinated mice were again shown to strongly reduce the time-course of splenic infection. However addition of both effects was observed for a short time only two and three weeks post-challenge and only when the serum was injected after the challenge. In contrast, no additive or even an antagonistic effect was observed after the 21st day. Liver infection was not notably modified by both immune serum or splenic cells (except increment of initial colonisation by serum) until the 21st day when both helped reduce the course of infection. However again no additive effect was observed.(ABSTRACT TRUNCATED AT 250 WORDS)