Immunogenic activity of a cell wall fraction extracted from Brucella abortus in guinea-pigs

A cell wall fraction (F8) extracted by boiling sodium dodecylsulfate at 4 % from Brucella abortus 99S was used with oil adjuvant to vaccinate groups of ten guinea-pigs, at doses equivalent to 1 X 10(9) and 1 X 10(10) bacteria, once or twice at 3 month intervals. H38 vaccine, a total cell vaccine from formalized B. melitensis 53 H38, was used as a reference, at doses 3 X 10(8) and 3 X 10(9) bacteria. These doses were chosen since they have about the same vaccinal activity in mice being respectively equal to 10 and 100 mice optimal dose (MOD). One extra-group of guinea-pigs received two injections of 100 microgram of smooth-lipopolysaccharide (LPS-S) of B. melitensis 16M, in adjuvant. Control group received the adjuvant only. Guinea-pigs were challenged 3 months after the last vaccination with 5,000 colony-forming units of B. abortus 544, and autopsied 40 days later. The spleen and 8 lymph nodes were cultured: a guinea-pig is considered as protected if no Brucella was found in any sample. Protection afforded by the two vaccines is dose-dependent. H38 vaccine gives a better protection (infected 24 %) than F8 (46 %) since a higher dose is needed to obtain the same level of protection: i. e., 100 MOD of F8 is about equal to 10 MOD of H38 (35 and 37 % respectively). Contrary to what was previously shown in mice, recall does not improve the immunity and LPS-S does not vaccinate at all.