Figure 6: GC size and average number of T cells per GC in mice immunized 9 d previously with 100 μg alum-precipitated protein antigen. Results are shown for normal littermate controls (•); CTLA4-Ig tg mice treated with anti-CD28 mAb and either a control Ig fusion protein (control-Ig, 100 μg; ▵) or OX40-Ig (100 μg; X). Results show the mean GC size (a) and T cells/GC (b). In each mouse, 20 consecutive GC areas were measured, and the numbers of individual CD3 cells within GCs were counted. Results are representative of two separate experiments.

Mentions: The lack of GC formation in CTLA4-Ig tg mice can be reversed by a single injection of agonistic anti-CD28 Ab (Fig. 6 a). These mice develop large GCs, unlike CTLA4-Ig tg mice given control hamster Ig (data not shown). Production of specific IgG Ab is also restored, and there is evidence of affinity maturation (data not shown). Blocking OX40 interactions with a fusion protein between murine OX40 and human IgG1 (OX40-Ig) allowed us to test our hypothesis that the restoration of GC formation by anti-CD28 treatment is dependent on OX40 signaling. CTLA4-Ig tg mice were immunized with alum-precipitated protein intraperitoneally, and 1 d later were given anti-CD28 mAb (100 μg) with either OX40-Ig (100 μg in three doses on days 1, 2, and 3) or a control Ig fusion protein. Because CTLA4-Ig tg mice have no GCs, injection of mAb to CD28 allows accurate timing of their onset. Also, because CTLA4-Ig tg mice are tolerant to fusion proteins between human IgG1 and self-proteins, blockade is more likely to persist and be effective. The presence of CTLA4-Ig, which binds to CD80 and CD86 on activated B cells, controls for potential artifacts due to OX40-Ig binding to B cells, independent of its effect on OX40/OX40L blockade.

Walker LS, Gulbranson-Judge A, Flynn S, Brocker T, Raykundalia C, Goodall M, Förster R, Lipp M, Lane P - J. Exp. Med. (1999)

Bottom Line: This is associated with impaired interleukin 4 production and a lack of CXC chemokine receptor (CXCR)5 on CD4 T cells, a chemokine receptor linked with migration into B follicles.Germinal center formation is restored in CTLA4-Ig transgenic mice by coinjection of an agonistic monoclonal antibody to CD28, but this is substantially inhibited if OX40 interactions are interrupted by simultaneous injection of an OX40-Ig fusion protein.These data suggest that CD28-dependent OX40 ligation of CD4 T cells at the time of priming is linked with upregulation of CXCR5 expression, and migration of T cells into B cell areas to support germinal center formation.

Affiliation: Department of Immunology, University of Birmingham Medical School, Birmingham B15 2TT, United Kingdom.

Abstract: Mice rendered deficient in CD28 signaling by the soluble competitor, cytotoxic T lymphocyte-associated molecule 4-immunoglobulin G1 fusion protein (CTLA4-Ig), fail to upregulate OX40 expression in vivo or form germinal centers after immunization. This is associated with impaired interleukin 4 production and a lack of CXC chemokine receptor (CXCR)5 on CD4 T cells, a chemokine receptor linked with migration into B follicles. Germinal center formation is restored in CTLA4-Ig transgenic mice by coinjection of an agonistic monoclonal antibody to CD28, but this is substantially inhibited if OX40 interactions are interrupted by simultaneous injection of an OX40-Ig fusion protein. These data suggest that CD28-dependent OX40 ligation of CD4 T cells at the time of priming is linked with upregulation of CXCR5 expression, and migration of T cells into B cell areas to support germinal center formation.