Induction of autoimmunity. A role for the idiotypic network

Atherosclerosis in LDL-receptor knockout mice is accelerated by immunization with anticardiolipin antibodies

Atherosclerosis is a process initiated by accumulation of macrophages in distinct areas of endothelial cell damage and uptake of large amounts of lipids. Recently, it has been shown that the immune system plays an active part in the progression of the atherosclerotic plaque although its precise role has not yet been elucidated.

Anticardiolipin antibodies (aCL) are generally found in the sera of patients with the antiphospholipid syndrome (APS) and are associated with a prothrombotic state. Several authors have demonstrated that aCL can activate platelets and endothelial cells as well as increase oxidized low density lipoprotein (LDL) uptake by macrophages. In the present study we sought to assess the effect of immunization with aCL (Ab1, leading to the production of mouse aCL-Ab3) on the progression of atherosclerosis. Two groups of 8-weeks old female LDL-receptor knockout mice (n = 13 per group) were immunized with IgG purified from the serum of an APS patient or with normal human IgG, respectively. The aCL immunized mice developed high titres of 'self' aCL (detected using the standard aCL ELISA) as compared with the normal human IgG immunized mice, whereas no differences were noted between both study groups with respect to the serum lipid levels. The extent of fatty streak formation was significantly higher in the aCL immunized mice in comparison with the human IgG injected mice (mean aortic lesion size of 5308 ± 471 μm2 vs 1027 ± 184 μm2, respectively, P < 0.01). The immunohistochemical analysis of the atherosclerotic plaques from both mouse groups did not display differences in cellular composition.

The results of the study show that mouse aCL induced by immunization with human aCL from an APS patient enhance atherogenesis in LDL-RKO mice and imply that these antibodies may play a role in atherosclerosis development in patients with the APS.

Self-tolerance in a minimal model of the idiotypic network

We consider the problem of self-tolerance in the frame of a minimalistic model of the idiotypic network. A node of this network represents a population of B-lymphocytes of the same idiotype, which is encoded by a bit string. The links of the network connect nodes with (nearly) complementary strings. The population of a node survives if the number of occupied neighbors is not too small and not too large. There is an influx of lymphocytes with random idiotype from the bone marrow. Previous investigations have shown that this system evolves toward highly organized architectures, where the nodes can be classified into groups according to their statistical properties. The building principles of these architectures can be analytically described and the statistical results of simulations agree very well with results of a modular mean-field theory. In this paper, we present simulation results for the case that one or several nodes, playing the role of self, are permanently occupied. These self nodes influence their linked neighbors, the autoreactive clones, but are themselves not affected by idiotypic interactions. We observe that the group structure of the architecture is very similar to the case without self antigen, but organized such that the neighbors of the self are only weakly occupied, thus providing self-tolerance. We also treat this situation in mean-field theory, which give results in good agreement with data from simulation. The model supports the view that autoreactive clones, which naturally occur also in healthy organisms are controlled by anti-idiotypic interactions, and could be helpful to understand network aspects of autoimmune disorders.

Production and characterization of an anti-idiotypic single chain Fv that recognizes an anti-DNA antibody

A well-characterized recombinant anti-idiotype to an anti-DNA antibody can be useful for studies of the regulation of anti-DNA-producing B cells. Using a hybridoma technique, a monoclonal anti-idiotypic antibody, designated O2F3, was obtained, and its scFv gene was constructed. O2F3 single chain Fv (scFv) was produced against an idiotope of a monoclonal anti-DNA antibody, 3D8, that was obtained from an autoimmune-prone mouse, MRL-lpr/lpr. Here we describe the production and in vitro characterization of the O2F3 scFv, and compare it with its parent monoclonal antibody, O2F3 IgM. To characterize O2F3 scFv and O2F3 IgM, we generated recombinant 3D8 fragments, including 3D8 scFv, 3D8 VH, and 3D8 VL, that were used as antigens in several assays. ELISA and Western blot analysis showed that both O2F3 scFv and O2F3 IgM recognized a conformational determinant formed by the association of the variable region heavy and light chains of the 3D8 antibody, suggesting that O2F3 scFv retained a similar binding pattern to its parent O2F3 antibody. The idiotope recognized by O2F3 was shown by competitive ELISA to be outside of the DNA binding site of the 3D8 antibody. This characterized O2F3 scFv could be applied for the regulation of anti-DNA antibody production and the manipulation of recombinant antibody-based proteins to which toxins, enzymes, and chemical agents can be connected.

Immune complex-induced chronic and intense IL-4 independent IgG1-rheumatoid factor production in NZB mice

Immune complexes from the synovial fluid of rheumatoid arthritis (RA) patients, or artificial rheumatoid factors (RF)-like (antibody--antibody) immune complexes, induce a remarkably intense, sustained and selective immunoglobulin (Ig)G1 response under certain experimental conditions in mice. Because the IgG1 antibody response is extraordinarily strong, the role of interleukin (IL)-4, important for IgG1 synthesis, was investigated. Both C57BL/6 and NZB IL-4-deficient mice produced IgG1--RF antibodies after injection with RF-like immune complexes, although the antibody levels were slightly delayed compared to wild type mice. This shows that IL-4 is not obligatory in RF-like immune complex induced IgG1--RF production. A discrepancy in the decline of serum IgG1--RF was noted between NZB and C57Bl/6 mice. Serum IgG1-RF declined 43 days postinjection (p.i.), in C57BL/6 mice whereas high serum levels of IgG1--RF were maintained more than 100 days in the NZB mice, indicating different regulatory mechanisms in these mice. To study if the affinity for mouse IgG increased with time in NZB mice and thus become more directed against self, the cross-reactivity of the IgG1--RF antibodies with IgG from other species was investigated early and late after injection. It was, however, found that the cross-reactivity with IgG of human, goat and rabbit origin did not change between the two time points.

Protective long-term antibody memory by antigen-driven and T help-dependent differentiation of long-lived memory B cells to short-lived plasma cells independent of secondary lymphoid organs

Memory is a hallmark of immunity. Memory carried by antibodies is largely responsible for protection against reinfection with most known acutely lethal infectious agents and is the basis for most clinically successful vaccines. However, the nature of long-term B cell and antibody memory is still unclear. B cell memory was studied here after infection of mice with the rabies-like cytopathic vesicular stomatitis virus, the noncytopathic lymphocytic choriomeningitis virus (Armstrong and WE), and after immunization with various inert viral antigens inducing naive B cells to differentiate either to plasma cells or memory B cells in germinal centers of secondary lymphoid organs. The results show that in contrast to very low background levels against internal viral antigens, no significant neutralizing antibody memory was observed in the absence of antigen and suggest that memory B cells (i) are long-lived in the absence of antigen, nondividing, and relatively resistant to irradiation, and (ii) must be stimulated by antigen to differentiate to short-lived antibody-secreting plasma cells, a process that is also efficient in the bone marrow and always depends on radiosensitive, specific T help. Therefore, for vaccines to induce long-term protective antibody titers, they need to repeatedly provide, or continuously maintain, antigen in minimal quantities over a prolonged time period in secondary lymphoid organs or the bone marrow for sufficient numbers of long-lived memory B cells to mature to short-lived plasma cells.

Autoantigen-specific B cell activation in Fas-deficient rheumatoid factor immunoglobulin transgenic mice

In systemic autoimmune disease, self-tolerance fails, leading to autoantibody production. A central issue in immunology is to understand the origins of activated self-reactive B cells. We have used immunoglobulin (Ig) transgenic mice to investigate the regulation of autoreactive B cells with specificity for self-IgG2a (the rheumatoid factor [RF] specificity) to understand how normal mice regulate RF autoantibodies and how this fails in autoimmune mice. We previously showed that normal mice do not tolerize the AM14 RF clone, nor do they appear to activate it. Here we show that in Fas-deficient autoimmune mice, the picture is quite different. RF B cells are activated to divide and secrete, but only when the autoantigen is present. Thus, B cells that are ignored rather than anergized in normal mice can be stimulated to produce autoantibody in Fas-deficient mice. This demonstrates a novel developmental step at which intact Fas-Fas ligand signaling is required to regulate B cells in order to prevent autoimmunity. These data also establish the relevance of ignorant self-specific B cells to autoantibody production in disease and prove that in the case of the RF specificity, the nominal autoantigen IgG2a is the driving autoantigen in vivo.

Altered VH6-D-JH repertoire in human insulin-dependent diabetes mellitus and autoimmune idiopathic thrombocytopenic purpura

We have characterized the peripheral B cell repertoire in T cell-mediated insulin-dependent diabetes mellitus (IDMM) and in B cell-mediated autoimmune idiopathic thrombocytopenic purpura (AITP). The VH6-containing repertoire in adult patients with IDDM or AITP and healthy control subjects was investigated by PCR amplification using VH6- and JH-specific primers. Nucleotide sequence analysis of VH6-D-JH rearrangements showed an abnormally high frequency of somatic mutations in non-functional rearrangements from diabetic (3. 58 %) as well as AITP patients (3.18 %), compared to controls (0.4 % and 1.43 %, respectively; p < 0.05). In contrast, the mutation frequency among functional rearrangements was 2.4 - 3 times lower in patients compared to controls ( p < 0.05). Detailed analysis of the VH6 genes carrying mutations showed that the underlying mechanism for this observation is probably different for the two diseases. Analysis of D- and JH gene usage revealed additional deviations from the normal pattern. Taken together, these results suggest defects in the mechanisms controlling selection of the B cell repertoire in patients with IDDM or AITP.

Long-lived plasma cells: a mechanism for maintaining persistent antibody production

Current models suggest that continuous antigenic stimulation of memory B cells is required to maintain long-term antibody production. In view of recent developments concerning plasma cell longevity, a new model is described that incorporates the important role of long-lived plasma cells in sustaining persistent antibody responses.