LIPOPOLYSACCHARIDE FROM BRUCELLA-ABORTUS BEHAVES AS A T-CELL-INDEPENDENT TYPE-1 CARRIER IN MURINE ANTIGEN-SPECIFIC ANTIBODY-RESPONSES

In order to determine the carrier nature of lipopolysaccharide from Br ucella abortus (LPS-BA) in evoking humoral responses, normal and immun odeficient mice were immunized with trinitrophenyl (TNP)-conjugated LP S-BA (TNP-LPS-BA) and the responses were compared with those to known T-dependent and T-independent antigens. TNP-LPS-BA, like T-independent type 1 (TI-1) antigens such as TNP-BA and TNP-LPS from Escherichia co li (TNP-LPS-EC), generated anti-TNP responses in BALB/c, athymic BALB/ c nu/nu, and CBA/N mice. In contrast, -dinitrophenyl-beta-alanylglycyl glycyl-substituted keyhole limpet hemocyanin, a typical T-dependent an tigen, was not immunogenic in athymic mice, and TNP-Ficoll (T-independ ent type 2) was ineffective in eliciting humoral responses in CBA/N mi ce. These results indicate that LPS from B. abortus acts as a TI-1 car rier in generating antibody responses. In C3H/HeJ mice, TNP-LPS-BA gen erated higher-titer immunoglobulin G1 (IgG1), IgG2a, and IgG2b anti-TN P antibodies than TNP-LPS-EC. Compared with those from BALB/c mice, pu re resting B cells isolated from C3H/Hej mice exhibited a 30-fold lowe r proliferative response to LPS-EC, whereas the LPS-BA response was re duced to a lesser extent (5-fold). This suggests that the disparity ob served in antibody titers was due to different abilities of LPS from B . abortus and E. coli to stimulate C3H/HeJ B cells. The ability of LPS from B. abortus to act as a carrier in generating humoral immune resp onses indicates that LPS-BA can be substituted for whole B. abortus or ganisms in vaccine development.