Influence of Brucella endotoxins on the initiation of antibody-forming spleen cells in mice immunized with sheep red blood cells.

Changes in the formation of antibodies to sheep red blood cells (sRBC) in the presence of Brucella extracts was studied in mice whose spleen cells were assayed by the Jerne procedure. Two strains of female mice were employed. Brucella extracts were prepared: (i) by trichloroacetic acid extraction (LPSN), (ii) by phenol extraction (LPS), and (iii) by hot acetic acid hydrolysis (Ps). B. abortus LPSN and B. melitensis LPSN or LPS, administered with sRBC, stimulated the specific response to sRBC, but only at high doses of endotoxins. B. abortus LPSN and B. melitensis LPSN suppressed nonspecific responses against horse red blood cells (hRBC), in contrast to the typical events following administration of Serratia marcescens endotoxin (or endotoxins from other ubiquitous organisms). In CD-1 mice, B. abortus Ps depressed the specific anti-sRBC response. Attempts to presensitize mice with abortus LPSN resulted in a stimulation of the response to sRBC, but pretreatment with B. melitensis LPSN had an inhibitory effect. When injected alone, Brucella endotoxins activated anti-sRBC antibody-forming cells but not anti-hRBC cells. B. abortus Ps was unable to modify the background number of anti-sRBC cells and inhibited the hRBC response. These data suggest (i) that there exists a "common antigen" between Brucella cells and sRBC and (ii) that the so-called primary response to endotoxins from ubiquitous organisms represents a secondary response to already naturally sensitized animals.