There has recently been an increase in data indicating that autoimmune mechanisms are involved in the etiopathogenesis of idiopathic thrombocytopenic purpura (ITP) (1, 2). Although antibodies that react with platelets are found in most patients with ITP, the pathogenetic nature of the antibodies remains to be clarified . The discovery of an animal model for ITP has therefore been long-awaited. Here we have found that (NZW x BXSB)Fi (W/B Fi) mice, which develop lupus nephritis with myocardial infarction (3), show thrombocytopenia with age, and that this is due to the presence ofboth platelet-associated antibodies (PAA) and circulating antiplatelet antibodies.Recently, we have demonstrated that allogeneic bone marrow transplantation (ABMT) has curative effects on autoimmune diseases in (NZB x NZW)FI, BXSB, MRL/MP-lpr/lpr (MRL/lpr), and NOD mice (4-6) . These results prompted us to examine whether ABMT can be used to treat ITP. In the present study, we provide evidence that the transplantation of bone marrow from BALB/c mice to W/B F, mice does indeed have preventative and curative effects on ITP Materials and MethodsMice.Mice ofthe inbred strain BALB/c nu/nu, BALB/c, C57B/6, C3H/HeN, BXSB, NZW were raised under specific pathogen-free conditions in our animal facility. W/B F, males were obtained from the Nippon Shinyaku Research Laboratories, Kyoto, Japan.Staining Procedure andData Analysis.Platelet-rich plasma was obtained as described previously (7) . The platelets were suspended in 1% paraformaldehyde solution for 5 min. After

A small number of B cells are found in the thymus of normal mice. A population of B lymphocytes could be enriched to greater than 90% purity by isolating a low-density fraction on Percoll density gradients and then depleting T cells with a mixture of anti-Thy-1, CD4, and CD8 mAbs and complement. Enrichment was monitored by surface Ig staining and by functional studies (responsiveness to LPS, and to anti-mu plus IL-4). When the phenotype of these B cells was studied by flow cytometry, 60-80% had the phenotype Ly-1+ (CD5), Ia+, B220low (CD45R), and Mac-1+ (CD 11b). In contrast, splenic B cells lacked CD5 and CD11b and expressed higher levels of B220 and Ia antigens. These results indicate that most thymic B cells have the phenotype of the Ly-1 B cell subset, which was identified previously as a trace subpopulation in some peripheral tissues and is thought to play a role in autoantibody formation.

Conjugates of tumor-reactive antibody and toxins (immunotoxins) have been used to eradicate tumor cells in vitro and in vivo. Such immunotoxins are highly effective in killing murine leukemic cells in infiltrated bone marrow and should be useful in the bone marrow rescue approach for the treatment of cancer. Similar immunotoxins injected parentally can help to induce prolonged remissions in leukemic mice, and antigen-containing immunotoxins can induce immunologic unresponsiveness in vitro in normal murine splenocytes. Thus, long-range goals for the parental use of immunotoxins include the killing of cancer cells in vivo and the modulation of the immune response for therapeutic purposes.

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Distribution of FcR II, FcRIII, and FcR alpha on murine splenic B cells was examined by using FITC-labeled heat-aggregated IgG of each subclass and IgA. Almost 60 to 80% of B cells expressed both FcRII and FcRIII. However, FcR alpha was expressed on only a small proportion (6%) of B cells that co-expressed FcRII. By inhibition assays with the use of cold IgG of each subclass and IgA in addition to anti-FcRII mAb (2.4G2), it was found that IgG1, IgG2a, and IgG2b utilized the same receptor (FcRII), whereas IgG3 and IgA bound only to their unique receptors, FcRIII and FcR alpha, respectively. Immune complexes IC prepared by IgG1, IgG2a, IgG2b, and IgA anti-TNP mAb with TNP-coupled SRBC inhibited the polyclonal Ig secretion and proliferative responses of B cells stimulated with either IL-4 or LPS. The inhibition of B cell activation was associated with the blockade of the membrane depolarization. Moreover, IC prepared by these antibodies caused production of suppressive B cell factor (SBF) as is the case with rabbit IgG antibody to SRBC, and SBF thus prepared regulated antibody responses in an isotype-nonspecific manner. In contrast, no inhibition for these responses or production of SBF was attained by the IC of IgG3 antibody. We concluded that FcRII and FcR alpha mediates a suppressive signal for B cells by acting on the initial step of activation, whereas FcRIII lacks this activity.

Cloned TS4.44 cells, which were hybridized HAT-sensitive 3T3–4E cells with B cells stimulated by immune complexes produce a lymphokine, biochemical and biological characteristics of which are identical with those of conventional suppressive B cell factor (SBF) synthesized by Fc receptor bearing B cells stimulated with immune complexes. This factor is known to suppress B cell responses to antigen/mitogen. The present studies were carried out by using this hybridoma-derived SBF to characterize the large proportion of B cells sensitive to SBF and the small proportion of B cells resistant to it in terms of affinities of antibodies which these cells are able to produce. The treatment of normal spleen cells with SBF resulted in a 50–70% decrease in anti-dinitrophenyl (DNP) antibody production when the cells were transferred into X-ray-irradiated mice along with alum-precipitated dinitrophenyl-conjugated keyhole limpet hemocyanin (DNP-KLH). The affinity of anti-DNP antibody molecules produced in these mice was significantly lower than that of the controls, even if immunization was repeated. The target cells for SBF were B, and not helper T cells which might be involved in the process of affinity maturation. A single treatment of spleen cells in vitro with SBF was sufficient to abrogate the precursors committed to mediate high-affinity anti-DNP antibody responses, since the retreatment with SBF in vitro and transfer into the second irradiated recipients along with antigens of spleen cells of mice to which SBF-treated spleen cells were transferred 3 weeks before resulted in almost the same level of plaque-forming-cell-responses as in mice which received medium-treated, instead of SBF-treated spleen cells in the second cell transfer. This implies that the effect of SBF on the target B cells is selective and irreversible. It may be postulated that there are at least two types of B cell subpopulations in terms of the sensitivity to SBF: one is a SBF-resistant subset which is perhaps assigned to participate in the primary humoral immune response by producing antibody molecules with relatively low affinity, while the other is a SBF-sensitive subset which perhaps preferentially takes part in the secondary/memory response by producing those bearing high affinity.