Relative efficacy of intravenous immunoglobulin G in ameliorating thrombocytopenia induced by antiplatelet GPIIbIIIa versus GPIbalpha antibodies

Intravenous immunoglobulin G (IVIG) is used to treat idiopathic thrombocytopenic purpura (ITP). Although many patients benefit from IVIG, some are refractory to this therapy. ITP is characterized by platelet clearance mediated primarily by antiplatelet antibodies against GPIIbIIIa and/or the GPIbalpha complex. These 2 groups of antibodies may induce ITP through different mechanisms. We tested the hypothesis that IVIG may not be equally effective in preventing ITP caused by anti-GPIIbIIIa versus anti-GPIbalpha antibodies in mice. Thrombocytopenia was induced in BALB/c mice using monoclonal antibodies against either mouse GPIIbIIIa (JON1, JON2, and JON3) or GPIbalpha (p0p3, p0p4, p0p5, p0p9, and p0p11). Pretreatment with IVIG significantly ameliorated ITP in all anti-GPIIbIIIa-injected animals. Conversely, IVIG failed to prevent ITP in all anti-GPIbalpha-treated mice, except for p0p4. These results were repeated in C57BL/6 mice, and with different IVIG preparations. These data in mice suggest that patients with ITP mediated by anti-GPIbalpha antibodies may be less responsive to IVIG treatment.     

Therapeutic efficacy of intravenous immunoglobulin preparations depends on the immunoglobulin G dimers: studies in experimental immune thrombocytopenia

The clinical benefit of intravenous immunoglobulin (IVIG) preparations in the treatment of immune thrombocytopenic purpura (ITP) is supposed to be mediated by blockade of Fc gamma receptor--bearing phagocytes. In 2 experimental models for ITP, it is shown that the therapeutic efficacy of IVIG preparations is related to the IgG dimer content present in these preparations. A rat monoclonal antibody (mAb; MWReg30) directed to the murine platelet-specific integrin alpha(IIb)beta(3) (gpIIb/IIIa) was administered intraperitoneally either as bolus injection or continuous infusion. With bolus injection, the circulating platelet count dropped to almost zero within 3 hours. Pretreatment with cobra venom factor did not affect platelet depletion, whereas pretreatment with anti-Fc gamma RII/III mAb 2.4G2 or IVIG greatly reduced platelet clearance. With continuous infusion, platelet numbers reached a steady state after 4 days, at approximately 25% of control. This reduction in platelets was, however, not observed in mice deficient for the FcR gamma-chain, lacking Fc gamma RI, Fc gamma RIII, and Fc gamma RIII(-/-) mice. Infusion of a single dose of IVIG with a high IgG dimer content on the 4th day--ie, mimicking therapeutic administration--resulted in a platelet increase for several days. IVIG predominantly consisting of monomeric IgG had no effect on platelet numbers. In conclusion, continuous infusion of MWReg30 induces thrombocytopenia in mice by enhancing Fc gamma receptor--mediated clearance of platelets. In this model, it is shown that IgG dimers present in IVIG preparations are responsible for the increase in platelet counts. (Blood. 2001;98:1095-1099)     

Monoclonal antibodies that mimic the action of anti-D in the amelioration of murine ITP act by a mechanism distinct from that of IVIg

The mechanism of action of intravenous immunoglobulin (IVIg) and polyclonal anti-D-mediated reversal of immune thrombocytopenia (ITP) is still unclear. However, in a murine model of ITP, the therapeutic effect of IVIg appears to be wholly dependent upon the expression of the inhibitory Fc receptor, Fc gamma RIIB. We previously demonstrated that, similar to anti-D in humans, 2 erythrocyte-reactive monoclonal antibodies (TER119 and M1/69) ameliorated murine ITP and inhibited reticuloendothelial system (RES) function at doses that protected against thrombocytopenia. The current study evaluated the involvement of the inhibitory and activating Fc receptors, Fc gamma RIIB and Fc gamma RIIIA, respectively, in the TER119 and M1/69-mediated inhibition of thrombocytopenia. In contrast to IVIg, in Fc gamma RIIB-deficient mice, both monoclonal antibodies ameliorated ITP and both significantly down-regulated the level of expression of the activating Fc gamma RIIIA in splenic macrophages. These results indicate that anti-erythrocyte antibodies that ameliorate ITP act independently of Fc gamma RIIB expression but are dependent upon the activating Fc gamma RIIIA.     

Immunological effects of intravenous gammaglobulin treatment in childhood idiopathic thrombocytopenic purpura

The effects of high-dose intravenous IgG treatment on circulating and bound platelet antibodies, immunoglobulin synthesis and lymphocyte subpopulations were studied in children with idiopathic thrombocytopenic purpura (ITP). The levels of circulating IgM platelet antibodies increased in 3 patients and remained unaffected in 9 others after treatment. Platelet-associated IgM levels decreased in all patients, while platelet-associated IgG decreased in 10 out of 12 patients. The spontaneous non-specific immunoglobulin synthesis by peripheral lymphocytes determined with a protein-A plaque assay was rather increased than suppressed. There was no consistent effect on the frequency of surface immunoglobulin-positive lymphocytes (B cells), although an increase was seen after treatment in 5 out of 8 patients, due to an increased number of surface IgM-positive cells. The frequencies of T cells and T cell subpopulations determined with the help of monoclonal antisera (OKT 3, 4, 8) were not affected. No major side effects were observed and serum transaminase levels were normal during and after the treatment. It is suggested that the short-term effect of IgG treatment in ITP is not due to an immunomodulating or suppressive action. It might, in some patients, be due to interaction of the IgG with antibody or immune complex binding to platelets.     

The neonatal Fc receptor (FcRn) is not required for IVIg or anti-CD44 monoclonal antibody-mediated amelioration of murine immune thrombocytopenia

To definitively determine whether the neonatal Fc receptor (FcRn) is required for the acute amelioration of immune thrombocytopenia (ITP) by IVIg, we used FcRn-deficient mice in a murine ITP model. Mice injected with antiplatelet antibody in the presence or absence of IVIg displayed no difference in platelet-associated IgG between FcRn deficient versus C57BL/6 mice. FcRn-deficient mice treated with high-dose (2 g/kg) IVIg or a low-dose (2 mg/kg) of an IVIg-mimetic CD44 antibody were, however, protected from thrombocytopenia to an equivalent extent as wild-type mice. To verify and substantiate the results found with FcRn-deficient mice, we used β(2)-microglobulin-deficient mice (which do not express functional FcRn) and found that IVIg or CD44 antibody also protected them from thrombocytopenia. These data suggest that for both high-dose IVIg as well as low-dose CD44 antibody treatment in an acute ITP model, FcRn expression is neither necessary nor required.     

Specific antiplatelet autoantibodies in patients with antiphospholipid antibodies and thrombocytopenia

By means of immunoblotting and monoclonal antibody immobilization of platelet antigens (MAIPA) we have studied the specificity of antiplatelet antibodies in patients with antiphospholipid antibodies and thrombocytopenia defined as presence of anticardiolipin IgG and a platelet count below 100 × 10⁹/l. The study group consisted of 10 patients with systemic lupus erythematosus (SLE), 8 patients with primary anti-phospholipid syndrome (PAPS) and 16 patients with idiopathic thrombocytopenic purpura (ITP). The comparison group was formed by 17 patients with classical chronic ITP without anticardiolipin IgG. We identified the 80–100, 130–150 and 150–170 KD surface proteins that comigrate with GPIIIa, GPIIb and GPIb and a 50–70 KD cytoplasm band by immunoblot. In patients with classical chronic ITP, the prevalence of the antiplatelet antibodies against GPIIIa was 53% on immunoblot assay and 47% on MAIPA. In ITP patients who had also anti-phospholipid antibodies in serum, the percentage of reactivity to GPIIIa declined to 37% on immunoblot and 21 % on MAIPA but it was not statistically different from the percentage observed in patients with classical ITP. Autoantibodies to platelet surface glycoproteins were almost absent in SLE and PAPS patients, who showed a significant prevalence (78%) of IgG reactivity to the 50–70 KD internal platelet protein which was frequently encountered also in patients with ITP and aPL (56%). Our study provides additional evidence that platelet antigens in patients with phospholipid-associated secondary immune thrombocytopenia are different from those of primary ITP, and that surface glycoproteins were not involved.     

Comparison of the effects of antibody-coated liposomes, IVIG, and anti-RBC immunotherapy in a murine model of passive chronic immune thrombocytopenia

The present work evaluated antibody-coated liposomes as a new treatment strategy for immune thrombocytopenic purpura (ITP) through the use of a mouse model of the disease. Effects of antimethotrexate antibody (AMI)-coated liposomes and intravenous immunoglobulin (IVIG)-coated liposomes (15, 30, 60 micromol lipid/kg) were compared with the effects of IVIG (0.4, 1, 2 g/kg) and anti-red blood cell (anti-RBC) monoclonal antibody immunotherapy (TER119, 5, 15, 25, and 50 microg/mouse) on MWReg30-induced thrombocytopenia. Each treatment was found to attenuate thrombocytopenia in a dose-dependent manner and, consistent with previous work, IVIG was found to increase antiplatelet antibody clearance in a dose-dependent manner. TER119 demonstrated greater effects on thrombocytopenia relative to other therapies (peak platelet counts: 224% +/- 34% of initial platelet counts for 50 microg TER119/mouse versus 160% +/- 34% for 2 g/kg IVIG, 88% +/- 36% for 60 micromol lipid/kg AMI-coated liposomes, and 80% +/- 25% for 60 micromol lipid/kg IVIG-coated liposomes). However, the effects of TER119 were associated with severe hemolysis, as TER119 decreased RBC counts by approximately 50%. The present work demonstrated that antibody-coated liposomes attenuated thrombocytopenia in this model at a much lower immunoglobulin dose than that required for IVIG effects and, in contrast with TER119, antibody-coated liposomes increased platelet counts without altering RBC counts.     

Effects of intravenous immunoglobulin on platelet count and antiplatelet antibody disposition in a rat model of immune thrombocytopenia

Experiments were conducted to investigate the effects of intravenous immunoglobulin (IVIG) in a rat model of immune thrombocytopenia (ITP). Rats were pretreated with 0 to 2 g/kg IVIG and then challenged with an antiplatelet antibody (7E3, 8 mg/kg). IVIG effects on 7E3-induced thrombocytopenia and on 7E3 pharmacokinetics were determined. IVIG pretreatment led to significant changes in the degree and time-course of 7E3-induced thrombocytopenia (P =.031). Nadir percent platelet counts were 121% to 279% greater in animals treated with IVIG (0.4-2 g/kg) than in animals receiving 7E3 alone. IVIG treatment also led to dose-dependent increases in 7E3 clearance (P <.001), with more than 2-fold increases in 7E3 clearance seen following the highest dose of IVIG. In vitro experiments showed that IVIG effects on platelet count are not likely due to anti-idiotypic inhibition of 7E3-platelet binding and that IVIG did not directly bind to 7E3. Consequently, IVIG-7E3 binding cannot explain the increase of 7E3 clearance following IVIG treatment. We propose that the observed increase in 7E3 clearance with IVIG therapy is due to saturation of the FcRn salvage receptor for IgG. The importance of the effect of IVIG on 7E3 clearance to the prevention of thrombocytopenia in these animals is unclear at present; nonetheless, these data provide experimental support for a new mechanism of IVIG action in ITP (ie, IVIG-mediated increases in antiplatelet antibody elimination). This model of ITP will be useful for further investigations of IVIG mechanism of action and for development of new therapies for ITP.     

Two human monoclonal antiplatelet autoantibodies established from patients with chronic idiopathic thrombocytopenic purpura

Two human hybridomas secreting antiplatelet autoantibodies were established by somatic cell fusion using splenocytes from two patients with chronic idiopathic thrombocytopenic purpura (ITP). These monoclonal antibodies, HT7F and HT8C, were of the IgM isotype and reacted with autologous and allogeneic platelets fixed with paraformaldehyde (PFA). They also bound to fresh platelets. An elution study showed that eluates from allogeneic platelets reacted with autologous platelets. These results indicated that HT7F and HT8C were autoantibodies recognizing a site on the platelet surface. Both monoclonal antibodies were able to induce complement activation in vitro. HT7F was demonstrated to bind to a platelet protein having a molecular mass of 105 kDa under both nonreducing and reducing conditions. No human hybridoma synthesizing antibody against 105 kDa platelet protein has been reported to date. These antibodies may play a role in the pathogenesis of thrombocytopenia in some ITP patients.     

Amelioration of murine immune thrombocytopenia by CD44 antibodies: a potential therapy for ITP?

To explore the potential for monoclonal antibodies as a treatment for immune thrombocytopenia (ITP) and to further explore their mechanisms of action, we tested 8 monoclonal CD44 antibodies in murine ITP and found 4 antibodies that could successfully ameliorate ITP; 2 of these antibodies function at a full 3-log fold lower dosage compared with IVIg. Further characterization of the 2 most successful antibodies (5035-41.1D and KM114) demonstrated that, similar to IVIg: (1) the presence of the inhibitory IgG receptor FcγRIIB was required for their ameliorative function, (2) complement-deficient mice responded to anti-CD44 treatment, and (3) human transgenic FcγRIIA-expressing mice also responded to the CD44 therapeutic modality. Dissimilar to IVIg, the Fc portion of the CD44 antibody was not required. These data demonstrate that CD44 antibodies can function therapeutically in murine ITP and that they could potentially provide a very-low-dose recombinant therapy for the amelioration of human ITP.     

Studies of IgG subclasses of anti-erythrocyte antibodies contained in human plasma preparation products

Anti-A and anti-B antibodies (1: 1-1: 1, 024) of IgM or IgG type of the titers 1: 1-1: 1, 024 were detected in all of the lots of heat-treated human plasma protein (38 Lots), albumin (15 Lots), factor VIII or IX products (9 Lots) and immune globulin preparations for intravenous use (IVIG) (20 Lots) examined. Twelve out of 20 lots of IVIG contained unexpected anti-erythrocyte antibodies of IgG type. Though IgG1 antibody was detected in all of these 12 lots, antibodies composed of all subclasses including IgG3 could be detected in only 8 lots of them, all showing the anti-erythrocyte antibody titer of IgG type over 1:64. Conversely, none of the lots, in which the titer was less than 1:32, contained IgG3 antibodies. A patient of chronic ITP, 28-year-old female of blood type A and Rh-positive, showed contradictive results between the main (A type) and the accessory test (O type) of red blood cell grouping, accompanied with hemolytic anemia, following intravenous high-dose immune globulin therapy (400 mg/kg x successive 5 days), which was attributable to the anti-A antibody of IgG type composed of IgG1,2,3,4 in the IVIG administered. For high dosage administration of human plasma preparation products, those containing only low titer of unexpected anti-erythrocyte antibody should be selected.     

Immunologic thrombocytopenic purpura in patients at risk for AIDS

HIV-seropositive homosexuals, narcotic addicts and hemophiliacs develop a new syndrome of immunologic thrombocytopenic purpura (ITP) which is clinically indistinguishable from classic autoimmune thrombocytopenic purpura (ATP) with respect to increased megakaryocytes in the bone marrow, peripheral destruction of antibody-coated platelets, negative serology for SLE, response to treatment with prednisone and/or splenectomy. Eleven of 79 homosexual patients have developed AIDS 2 to 43 months after the diagnosis of ITP (mean, 22 months). The mechanism of the ITP appears to be different in homosexuals and narcotic addicts when compared to classic ATP. Homosexuals and narcotic addicts have markedly elevated platelet-bound IgG and C3C4 (2.5-4-fold ATP levels), PEG-precipitable circulating immune complexes and anti-F(ab')2 antibodies (absent in ATP). There is no inverse relationship between platelet-bound IgG and platelet count and platelet antibody is usually not elutable from washed platelets as is the case with classic ATP. Homosexual patients do not have 7S platelet antibody in their sera as do classic ATP patients, but appear to have immune complex deposition on their platelets, possibly due to the presence of anti-F(ab')2 antibodies. Narcotic addict patients do have detectable 7S platelet antibody but also appear to have immune complex deposition on their platelets, possibly due to anti-F(ab')2 antibodies. The anti-F(ab')2 antibodies are of the IgG class. They react with autologous, homologous patient and healthy control F(ab')2 fragments. Some anti-F(ab')2 antibodies have broad reactivity, others are more limited. It is postulated that some of the anti-F(ab')2 antibodies may be responsible for the thrombocytopenia.     

Exacerbation of autoantibody-mediated thrombocytopenic purpura by infection with mouse viruses

Antigenic mimicry has been proposed as a major mechanism by which viruses could trigger the development of immune thrombocytopenic purpura (ITP). However, because antigenic mimicry implies epitope similarities between viral and self antigens, it is difficult to understand how widely different viruses can be involved by this sole mechanism in the pathogenesis of ITP. Here, we report that in mice treated with antiplatelet antibodies at a dose insufficient to induce clinical disease by themselves, infection with lactate dehydrogenase-elevating virus (LDV) was followed by severe thrombocytopenia and by the appearance of petechiae similar to those observed in patients with ITP. A similar exacerbation of antiplatelet-mediated thrombocytopenia was induced by mouse hepatitis virus. This enhancement of antiplatelet antibody pathogenicity by LDV was not observed with F(ab')2 fragments, suggesting that phagocytosis was involved in platelet destruction. Treatment of mice with clodronate-containing liposomes and with total immunoglobulin G (IgG) indicated that platelets were cleared by macrophages. The increase of thrombocytopenia triggered by LDV after administration of antiplatelet antibodies was largely suppressed in animals deficient for gamma-interferon receptor. Together, these results suggest that viruses may exacerbate autoantibody-mediated ITP by activating macrophages through gamma-interferon production, a mechanism that may account for the pathogenic similarities of multiple infectious agents.     

Effects of IgG and its F(ab')2 fragments of some patients with idiopathic thrombocytopenic purpura on platelet aggregation

OBJECTIVES: To make humanized monoclonal antibodies by phage surface display technology, we screened out the specific anti-platelet glycoproteins (GPs) IgG antibody from patients with chronic idiopathic thrombocytopenic purpura (ITP), which can inhibit platelet aggregation. METHODS: We studied plasmas from 68 patients with ITP for the presence of IgG antibodies specific for GPIIb/IIIa and/or GPIb/IX using modified monoclonal antibody immobilization of platelet antigen assays. The IgG antibody and its F(ab')(2) fragments of the positive plasmas which could inhibit platelet aggregation function were prepared and purified. Their immunoreactivity to platelet GPs and effects on platelet function were further analyzed. RESULTS: GPIIb/IIIa- and GPIb/IX-specific antibodies were found in 21 and 19 patients, respectively. Six of them had antibodies against both GP complexes. Among the 34 positive plasmas, four with positive anti-GPIIb/IIIa autoantibody showed significant inhibition of platelet aggregation induced by adenosine diphosphate (ADP), whereas one with GPIb/IX-specific antibody inhibited ristocetin-induced platelet aggregation. The purified IgG and its F(ab')(2) fragments from two patients not only retained the ability to bind to platelet GPs but also impaired the in vitro ADP-induced platelet aggregation. CONCLUSIONS: F(ab')(2) portion of the IgG is a functional fragment, which is responsible for the autoantibody interaction with platelet GPs in ITP, and some of them also affect platelet function, which can be used to develop completely humanized anti-GPIIb/IIIa small molecular phage antibody.     

Thrombocytopenic purpura in narcotics addicts

Since November 1982 we have seen an association of thrombocytopenic purpura with chronic narcotic addiction in 70 patients with a mean platelet count of 53000 +/- 4000 (SE); 33 had stopped taking intravenous drugs for an average of 21.2 +/- 4.7 months; 13 of 15 had elevated antibody titers for a virus related to the acquired immunodeficiency syndrome. Platelet-bound IgG, IgM, and complement levels were 16.7-, 5.6-, and 3.1-fold greater than control values, respectively, and 2.6-, 1.9-, and 2.4-fold greater than values in 25 patients with classic autoimmune thrombocytopenic purpura studied at the same time. Thirty-three of thirty-six addicts had elevated circulating immune complexes, whereas 8 patients with autoimmune thrombocytopenia had no elevation. Eleven of eighteen addicts had positive serum platelet-reactive IgG titers, compared to 5 of 19 patients with classic autoimmune thrombocytopenia. The platelet-reactive IgG in sera of addicts was composed of 7S IgG antibody as well as high molecular weight (immune complex) IgG. Thus, chronic addicts appear to have a new immunologic platelet disorder associated with the presence of 7S IgG antiplatelet antibody, like patients with classic autoimmune thrombocytopenic purpura, and immune complex associated nonspecific platelet IgG, like male homosexual patients with thrombocytopenia.     

Detection of specific circulating antigen, immune complexes and antibodies in human hydatidosis from Turkana (Kenya) and Great Britain, by enzyme-immunoassay

Circulating antigen, specific immune complexes (IgG and IgM) and specific antibodies (IgG, IgM, IgE and IgA) were detected by enzyme-linked immunosorbent assay (ELISA) in the sera of hydatid (Echinococcus granulosus) patients from Turkana (Kenya) and the UK. Specific IgG and IgM antibodies predominated in current UK hydatid infections, while all classes of specific antibodies were lower in the Turkana patients. Circulating antigen, detected in 3% polyethylene glycol (PEG) precipitated complexes, using peroxidase conjugated hyperimmune human hydatid IgG (Fab) was more specific in ELISA than either antibody or immune complex assays where peroxidase conjugated anti-human IgG was used. Anti-human immunoglobulin ('rheumatoid' factor) was not detected in hydatid sera. Serum antigen, specific IgM immune complexes and specific IgM antibodies were associated with UK cases of current hydatid infection in contrast to patients with previous histories of hydatidosis. In 3 hydatid patients (from UK) levels of circulating antigen and specific IgM immune complexes rapidly declined within 1-4 months after surgical cyst removal. The detection of specific IgG and antigen in PEG precipitated immune complexes from false-negative/low responder Turkana hydatid sera, suggests that antibody 'mopping' by specific antigen may be occurring. After SDS-PAGE/immunoblotting analysis, antigen of mol. wt 67 000, present in hydatid cyst fluid and protoscoleces, was identified as putative circulating antigen in 3% PEG precipitates of sera from albendazole treated hydatid patients.     

Antiphospholipid antibodies (APLA) in immune thrombocytopenic purpura (ITP) and antiphospholipid syndrome (APS)

Antiphospholipid antibodies (APLA) are associated with anti-phospholipid syndrome (APS), a thrombotic disorder, but they are also frequently detected in immune thrombocytopenic purpura (ITP), a bleeding disorder. To investigate possible differences of APLA between these two disorders, we assayed IgG and IgM APLA by ELISA in 21 patients with ITP and 33 with APS. The APLA reacting against two protein target antigens, beta(2)-glycoprotein 1 (beta2GP1) and FVII/VIIa, and four phospholipids [cardiolipin (CL), phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylethanolamine (PE)] as well as lupus anticoagulant (LA) were analyzed. We made the following observations: (i) IgG and IgM antibodies to beta2GP1 and IgM antibodies to FVII/VIIa were more common in APS than ITP, P < 0.05, while IgG antibodies against the phospholipids (aCL, aPC, aPS, aPE) were more common in ITP than APS, P < 0.05; (ii) multiple APLA > or =3 antigens) were more frequent in APS than ITP, P < 0.05; (iii) LA was frequently associated with APS but was absent in ITP; (iv) APLA is quite common in ITP: two-thirds were positive for at least one APLA. In summary, APLA are prevalent in ITP but their profile differs from APS. In APS, antibodies were predominantly against beta2GP1 and 80% had positive LA, while in ITP the APLA reacted most often with the phospholipids without LA. The difference in APLA may result in opposite clinical manifestations in two disorders.     

NZB mouse system for production of monoclonal antibodies to weak bacterial antigens: isolation of an IgG antibody to the polysaccharide capsules of Escherichia coli K1 and group B meningococci.

A system for the production of monoclonal antibodies, particularly of the IgG type, against weakly immunogenic bacterial polysaccharide antigens is described. This system, which is based on the autoimmune NZB mouse strain, has been used to produce a monoclonal IgG2a antibody against the meningococcus group B and Escherichia coli K1 polysaccharides, identical homopolymers of alpha (2----8)-linked units of N-acetylneuraminic acid that are extremely poor immunogens. Comparison of the humoral immune responses of normal BALB/c mice and autoimmune NZB mice to hyperimmunization with group A, B, and C meningococci showed that, although both strains mounted a weak meningococcal B polysaccharide-specific IgM response, only the NZB strain mounted an IgG response. Similarly, NZB mice mounted a stronger IgG response to the more immunogenic group C meningococcal polysaccharide than did BALB/c mice, although this difference was less pronounced than that observed with meningococcal B polysaccharide. No difference between the two strains of mice was demonstrable with the strongly antigenic group A meningococcal polysaccharide. These results indicate that the NZB system may be generally useful for the production of monoclonal antibodies against weakly antigenic bacterial determinants.     

IgM antibodies induce the production of antibodies of the same specificity.

Injection in normal mice of IgM antibodies against sheep erythrocytes or dextran, in the form of an immune serum depleted og IgG, induces direct plaque-forming cells of the same specificity as the injected antibodies. The response is 10--70 times higher than the background plaque-forming cell titer of untreated control mice. Nanogram amounts of IgM induce a detectable response, and a ceiling is reached with a few hundred nanograms of monoclonal IgM. The inducing agent is not residual antigen: (i) treatment of the injected material and the recipients with dextranase abolishes the immunogenicity of dextran, but not the response to anti-dextran IgM; (ii) monoclonal IgM specific for sheep erythrocytes or trinitrophenyl likewise induces plaque-forming cells of the respective specificity, but variant hybridoma products (in which the light chain is that of the myeloma parent) are inactive. In normal mice, IgM-induced antibody responses were observed with antibodies to both thymus-dependent and thymus-independent antigens, but such could not be induced in athymic (nude) mice. Because the mechanism underlying this phenomenon would operate also in a normal immune response and, presumably, in the normal dynamic state of the immune system of unstimulated animals, a network regulation among the elements of the immune system itself is implied.     

Immune thrombocytopenic purpura: autoimmune or immune complex disease?

To assess the pathogenic role of circulating immune complexes (CIC) in idiopathic thrombocytopenic purpura (ITP), 39 patients with ITP were compared to 17 patients with other forms of thrombocytopenia (hypersplenism (N = 12), impaired thrombopoiesis (3), thrombocytopenia of unknown origin (2)) and six nonthrombocytopenic subjects. In all patients, platelet mean life span (MLS), platelet associated IgG (PAIgG), as well as circulating anti-platelet antibodies and C1q binding activities were determined. In most cases, immune complex solubilization capacity (ICSC) and immune complex precipitation inhibition capacity (ICPIC) of sera were also assessed. All patients with ITP had a reduced platelet MLS, but PAIgG was elevated in only 16 out of 24 patients with chronic ITP, in six out of 10 patients with acute ITP and in four out of five patients with secondary ITP. In the group of patients with thrombocytopenia due to splenomegaly, seven out of 12 patients had elevated PAIgG while the platelet MLS was only slightly reduced. Of the 39 patients with ITP only one with secondary ITP had C1q binding material in his serum, as opposed to six out of 12 thrombocytopenic patients with splenomegaly. Whereas only three patients with ITP had abnormal immune-complex modulating capacities, such deviations were found in seven out of 12 patients with thrombocytopenia due to splenomegaly. We conclude that our data render the role of CIC in the pathogenesis of ITP very questionable.