BruceUa abortus may be useful as a component of vaccines. This is because it possesses several unique properties as a carrier that enable it to stimulate human B cells even in the relative absence of T cells. Human immunodeficiency virus type 1 proteins conjugated to B. abortus could induce neutralizing antibodies against human immunodeficiency virus type 1. Recently we showed that the characteristics of lipopolysaccharide (LPS) derived from B. abortus are similar to those of the whole bacterium in that the LPS acts as a T-independent type 1 carrier in mice. In this study we wanted to determine whether LPS derived from B. abortus is associated with the adverse effects seen with other bacterial endotoxins. LPS purified from B. abortus by butanol extraction was shown to have <2% (wt/wt) contamination by protein and < 1% (wt/wt) contamination by nucleic acids and to contain 1% (wt/wt) ketodeoxyoctanic acid. Compared with LPS derived from Escherichia coli, B. abortus LPS was 10,000-fold less potent in eliciting fever in rabbits, 268-fold less potent in killing D-galactosamine-sensitized mice, and 1,400-fold and 400-fold less potent in inducing interleukin-1 and tumor necrosis factor alpha production, respectively. These results suggest that B. abortus LPS is much less likely than the LPS from E. coli to evoke endotoxic shock; therefore, it may be feasible to incorporate B. abortus as a component of vaccines.

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In order to determine the carrier nature of lipopolysaccharide from Brucella abortus (LPS-BA) in evoking humoral responses, normal and immunodeficient mice were immunized with trinitrophenyl (TNP)-conjugated LPS-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 coli (TNP-LPS-EC), generated anti-TNP responses in BALB/c, athymic BALB/c nulnu, and CBAIN mice. In contrast, N-2,4-dinitrophenyl-j8-alanylglycylglycyl-substituted keyhole limpet hemocyanin, a typical T-dependent antigen, was not immunogenic in athymic mice, and TNP-Ficoll (T-independent type 2) was ineffective in eliciting humoral responses in CBA/N mice. These results indicate that LPS from B. abortus acts as a TI-i carrier in generating antibody responses. In C3H/HeJ mice, TNP-LPS-BA generated higher-titer immunoglobulin Gi (IgGI), IgG2a, and IgG2b anti-TNP antibodies than TNP-LPS-EC. Compared with those from BALB/c mice, pure resting B cells isolated from C3H/HeJ mice exhibited a 30-fold lower proliferative response to LPS-EC, whereas the LPS-BA response was reduced to a lesser extent (5-fold). This suggests that the disparity observed 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 responses indicates that LPS-BA can be substituted for whole B. abortus organisms in vaccine development. * Corresponding author. polysaccharides such as TNP-Ficoll are TI-2 antigens. Typically, TI-1 and TI-2 antigens are able to induce IgM antibody production in athymic nude mice, whereas a TD antigen, e.g., DNP-KLH, will induce little or no antibody

Human immunodeficiency virus type 1 (HIV-1) infection is associated with loss of function and numbers of CD4 ؉ T-helper cells. In order to bypass the requirement for CD4 ؉ cells in antibody responses, we have utilized heat-inactivated Brucella abortus as a carrier. In this study we coupled a 14-mer V3 loop peptide (V3), which is homologous to 9 of 11 amino acids from the V3 loop of HIV-1 MN, and gp120 from HIV-1 SF2 to B. abortus [gp120(SF2)-B. abortus]. Our results showed that specific antibody responses, dominated by immunoglobulin G2a in BALB/c mice, were induced by these conjugates. Sera from the immunized mice bound native gp120 expressed on the surfaces of cells infected with a recombinant vaccinia virus gp160 vector (VPE16). Sera from mice immunized with gp120(SF2)-B. abortus inhibited binding of soluble CD4 to gp120, whereas sera from mice immunized with V3-B. abortus were ineffective. Sera from mice immunized with either conjugate were capable of blocking syncytium formation between CD4 ؉ CEM cells and H9 cells chronically infected with the homologous virus. Sera from mice immunized with gp120(SF2)-B. abortus were more potent than sera from mice immunized with V3-B. abortus in inhibiting syncytia from heterologous HIV-1 laboratory strains. Importantly, in primary and secondary responses, V3-B. abortus evoked anti-HIV MN antibodies in mice depleted of CD4 ؉ cells, and sera from these mice were able to inhibit syncytia. These findings indicate that B. abortus can provide carrier function for peptides and proteins from HIV-1 and suggest that they could be used for immunization of individuals with compromised CD4 ؉ T-cell function.