Peripheral deletion of rheumatoid factor B cells after abortive activation by IgG

Abstract

Rheumatoid factor (RF) B cells proliferate during secondary immune responses to immune complexed antigen and antigen specific T cells, but higher affinity RFs are not detected except in patients with rheumatoid arthritis and other autoimmune diseases. Consequently, there must exist highly efficient mechanisms for inactivation of these higher-affinity RF B cell clones under normal circumstances. Exposure of transgenic mice expressing a human IgM RF to soluble human IgG in the absence of T cell help causes antigen specific B cell deletion in 2-3 days. The deletion is independent of the Fas/Fas ligand (FasL) pathway of apoptosis and is preceded by a phase of partial activation involving increase in cell size and expression of B7 and ICAM-1, and transient release of low levels of immunoglobulin. Complete B cell activation involving the formation of germinal centers and sustained high level RF secretion only occurs if T cell help is provided simultaneously. RF B cells exposed to tolerogen remain competent to secrete RF in vitro if provided with an appropriate antigenic stimulus and T cell help. Consequently, death of these cells is not preceded by anergy. Abortive activation/deletion of B cells by antigen in the absence of T cell-derived survival signals may represent the major mechanism for maintaining peripheral tolerance in B cells expressing higher affinity RF. The lack of anergy, and the potential for reactivation before death, provide a means for maintaining RF production under pathologic circumstances, such as may occur in the inflamed rheumatoid synovium.

Figures

Figure 1

Loss of hIgM RF-B cells is preceded by activation. AB29 mice were injected i.p. with 2 mg DHGG. Spleen cells were removed 1, 3, or 7 days after treatment, stained for surface expression of B220 (total B cells), hIgM, and the activation antigen B7.2 and then analyzed on the cytofluorograph. (A) Forward scatter (FSC) values of hIgM+/B220+ cells (TG+, □) and hIgM−/B220+ cells (TG−, ▪) from the same mice, as a measure of size. (B) Mean intensity of fluorescence (MIF) of B7.2 staining for hIgM+/B220+ cells (TG+, □) and hIgM−/B220+ cells (TG−, ▪) from the same mice, as a measure of B cell activation. Data shown are means ± SE for groups of three or four mice and represent a percentage of control levels seen on untreated AB29 mice. All time points were significantly different from controls for TG+ cells, no time points were significantly different from controls for TG− cells; P < 0.05.

Figure 2

Effect of encounter with soluble hIgG on the distribution of hIgM RF-expressing B cells in the spleen. (A–D) Immunohistochemical analysis of spleen sections from either uninjected AB29 mice (A) or AB29 mice, 3 days (B), or 7 days (C) after i.p. injection of 2 mg DHGG or 7 days after i.p. injection of DHGG and i.v. injection of 20 × 106 C57BL/6bm12 splenocytes. (D) (Low power views, ×100.)