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.
In the present study inactivated human immunodeficiency virus type 1 (HIV-1) was conjugated to Brucella abortus and tested for immunogenicity in normal and anti-L3T4-treated BALB/c mice. HIV-BA was more immunogenic than uncoupled HIV in normal mice, since 6-fold less virus in HIV-BA preparations elicited higher titer responses than HIV-1 alone. Furthermore, the HIV-BA antibody response reached higher levels before the HIV-1 response. Immunoblot analysis showed that most of the HIV-1 antigens were recognized by antibodies induced by either HIV-1 or HIV-BA. Isotype analysis revealed that HIV-1 induced similar levels of IgG1 and IgG2a antibodies, whereas the IgG2a responses to HIV-BA were more pronounced than the IgG1 response. These different IgG subclass patterns suggest that conjugation of HIV-1 to BA changed the immunogenic nature of HIV-1. The requirement for helper T cells was examined by immunizing mice that were depleted of CD4+ T cells by in vivo anti-L3T4 treatment. Under these conditions the IgG responses to HIV-1 were completely eliminated. Although HIV-BA antibody responses were markedly reduced in anti-L3T4-treated mice, anti-HIV-1 antibodies, mainly of the IgG2a isotype, were produced. The antibodies generated by HIV-1 and HIV-BA immunization were also tested for their ability to inhibit syncytia formed by infecting CD4 + CEM cells with gp160 vaccinia. Sera from normal mice, immunized with either HIV-1 or HIV-BA were capable of inhibiting syncytia. In contrast, following anti-L3T4 treatment, only mice immunized with HIV-BA, but not HIV-1, produced antibodies capable of inhibiting syncytia.
Movement of T-lymphocyte cell
IntroductionAlthough the T-cell receptor (TCR)-ligand interaction is critical for T-cell activation, other signals play a major role in T-cell activation. 1,2 This requirement for non-TCR signals has been called the "2 signal model" with TCR ligation being "signal 1," and the delivery of an additional costimulatory signal being "signal 2." [3][4][5] Although separate signaling pathways for costimulatory receptorligand pairs have been suggested to explain the enhancement of T-cell activation, a number of models have been proposed suggesting the costimulatory signal operates through enhancement of TCR-ligand interactions. One model states that "signal 1" correlates with inclusion or stabilization of TCR chains within specialized membrane compartments 6 referred to as rafts, DRMS, GEMS, or DIGS. These are sphingolipid cholesterol-rich membrane domains, which are associated with GPI-linked proteins, lck, LAT, ras, and other signaling molecules. 7 These domains are generally small with an estimated diameter of 70 nm in unstimulated cell membranes. 8 This "signal 1" activation is associated with protein phosphorylation and can signal for apoptosis. "Signal 2" correlates with coalescence of these small specialized membrane domains into a large domain at the T cell-antigen-presenting cell (APC) interface and is associated with lck SH3 interactions. 6 CD28-mediated costimulation facilitates raft coalescence at the T cell-APC contact site. 9 This "signal 2" activation is associated with interleukin (IL)-2 production, proliferation, and resistance to apoptosis in mature T cells. Ligation of costimulatory molecules CD28 and leukocyte function-associated antigen 1 (LFA-1) have also been shown to enhance actin-mediated transport of cell surface molecules toward the T cell-APC contact site. 10 In addition to simply moving toward the T cell-APC-interface, the TCR and other cell surface molecules arrange into a supramolecular activation complex (SMAC) with a defined geometry. 11,12 This leads to formation of an immunologic synapse [13][14][15] with the APCs that may not be an absolute requirement for all T-cell activation 16 but correlates with complete activation of CD4 ϩ T cells. 12 Thus, T-cell activation is a complex positional dance of varied receptor and signaling molecules. The timing and details of this molecular choreography are crucial in determining the varied outcomes of immune cell-antigen interactions. There is a complex cycle between molecular movements and signaling with each having effects on the other. In addition to T-cell interaction with antigen, T cells must control their motility and effector functions through overlapping signaling events. To dissect out these events, we have focused on the movement of CD43 during T-cell activation. The large size, extended structure, and negative charge of CD43 suggest it must be removed from the T cell-APC contact to prevent steric blockade of TCR-major histocompatibility complex (MHC)-peptide interactions. 17 CD43 may also negatively signal...
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