The HU177 Collagen Epitope Controls Melanoma Cell Migration and Experimental Metastasis by a CDK5/YAP-Dependent Mechanism.

Stromal components not only help form the structure of neoplasms such as melanomas, but they also functionally contribute to their malignant phenotype. Thus, uncovering signaling pathways that integrate the behavior of both tumor and stromal cells may provide unique opportunities for the development of more effective strategies to control tumor progression. In this regard, extracellular matrix-mediated signaling plays a role in coordinating the behavior of both tumor and stromal cells. Here, evidence is provided that targeting a cryptic region of the extracellular matrix protein collagen (HU177 epitope) inhibits melanoma tumor growth and metastasis and reduces angiogenesis and the accumulation of α-SMA-expressing stromal cell in these tumors. The current study suggests that the ability of the HU177 epitope to control melanoma cell migration and metastasis depends on the transcriptional coactivator Yes-associated protein (YAP). Melanoma cell interactions with the HU177 epitope promoted nuclear accumulation of YAP by a cyclin-dependent kinase-5-associated mechanism. These findings provide new insights into the mechanism by which the anti-HU177 antibody inhibits metastasis, and uncovers an unknown signaling pathway by which the HU177 epitope selectively reprograms melanoma cells by regulating nuclear localization of YAP. This study helps to define a potential new therapeutic strategy to control melanoma tumor growth and metastasis that might be used alone or in combination with other therapeutics.

Pathogenesis of the Novel Autoimmune-Associated Long-QT Syndrome.

BACKGROUND: Emerging clinical evidence demonstrates high prevalence of QTc prolongation and complex ventricular arrhythmias in patients with anti-Ro antibody (anti-Ro Ab)-positive autoimmune diseases. We tested the hypothesis that anti-Ro Abs target the HERG (human ether-a-go-go-related gene) K(+) channel, which conducts the rapidly activating delayed K(+) current, IKr, thereby causing delayed repolarization seen as QT interval prolongation on the ECG. METHODS AND RESULTS: Anti-Ro Ab-positive sera, purified IgG, and affinity-purified anti-52kDa Ro Abs from patients with autoimmune diseases and QTc prolongation were tested on IKr using HEK293 cells expressing HERG channel and native cardiac myocytes. Electrophysiological and biochemical data demonstrate that anti-Ro Abs inhibit IKr to prolong action potential duration by directly binding to the HERG channel protein. The 52-kDa Ro antigen-immunized guinea pigs showed QTc prolongation on ECG after developing high titers of anti-Ro Abs, which inhibited native IKr and cross-reacted with guinea pig ERG channel. CONCLUSIONS: The data establish that anti-Ro Abs from patients with autoimmune diseases inhibit IKr by cross-reacting with the HERG channel likely at the pore region where homology between anti-52-kDa Ro antigen and HERG channel is present. The animal model of autoimmune-associated QTc prolongation is the first to provide strong evidence for a pathogenic role of anti-Ro Abs in the development of QTc prolongation. It is proposed that adult patients with anti-Ro Abs may benefit from routine ECG screening and that those with QTc prolongation should receive counseling about drugs that may increase the risk for life-threatening arrhythmias.

Association of anti-acidic ribosomal protein P0 and anti-galectin 3 antibodies with the development of skin lesions in systemic lupus erythematosus.

OBJECTIVE: The specific autoantibodies and antigens that mediate systemic lupus erythematosus (SLE)-related organ injuries remain largely unknown. This study was undertaken to investigate the antibody-mediated immune response that leads to SLE skin lesions. METHODS: The study included 85 SLE patients with lupus-specific skin lesions and 31 without skin lesions. The reactivity of serum antibody with skin antigens was determined by immunoblotting using human foreskin as the substrate. Skin antigens were identified using mass spectrometry. Serum antibody was isolated by affinity purification and was injected intracutaneously into mouse skin to determine pathogenicity. Serum antibody levels were monitored by enzyme-linked immunosorbent assay. RESULTS: We determined that 78% of the patients with skin lesions had serum antibodies reactive with 35-kd and/or 25-kd skin antigens, which was significantly higher than the percentage of patients without skin lesions (P < 0.0001), suggesting a correlation between immune response and skin lesions. Acidic ribosomal protein P0 (RPLP0) and galectin 3 were 2 target antigens identified from 35-kd and 25-kd proteins, respectively. Purified serum anti-RPLP0 and anti-galectin 3 antibodies induced lupus-like histologic changes after intracutaneous injection. Anti-RPLP0 and anti-galectin 3 antibody levels were significantly higher in SLE patients than in healthy controls and decreased with skin recovery. Anti-galectin 3 antibody levels were not significantly higher in SLE patients than in patients with dermatomyositis or scleroderma, but strongly related to lupus cutaneous vasculitis. Additionally, levels of the 2 antibodies were positively correlated with leukopenia and C3 deficiency, and the anti-RPLP0 antibody level was also positively correlated with arthritis and SLE disease activity. CONCLUSION: Our findings indicate that the immune response mediated by serum anti-RPLP0 and anti-galectin 3 antibodies plays a key role in the pathogenesis of SLE skin lesions. These findings provide new insights into the mechanism of SLE-related organ disorders.

Anti-neuronal antibodies in patients with fragile X syndrome: is there a role of autoimmunity in its pathogenesis?

BACKGROUND: Fragile X syndrome (FXS) is a single-gene disorder with a broad spectrum of involvement, including cognitive and behavioural impairments of varying degrees with specific physical features and a strong association with autism. OBJECTIVES: In this study, the frequency of serum anti-neural antibodies was investigated in FXS patients who did and those who did not manifest autism spectrum disorders (ASD) in comparison to typically developing controls. METHODS: The study involved 23 males (mean age, 19.78 ± 6.56 years) who harboured a full mutation in the FMR1 gene. The control group comprised 19 healthy students (mean age 24.63 ± 1.89 years). Serum anti-neuronal antibodies were analyzed using Western blotting. RESULTS: Serum anti-neuronal antibodies were present in 10/23 (43.48%) FXS males. CONCLUSION: Serum anti-neuronal antibodies were found in a subgroup of FXS patients. Autistic symptoms in FXS may, in part, be caused by auto-immune factors. Further studies in larger patient and control groups are necessary to elucidate the aetiopathogenic role of anti-neuronal antibodies in FXS patients.

Blood group antigen-targeting peptide suppresses anti-blood group antibody binding to antigen in renal glomerular capillaries after ABO-incompatible blood reperfusion.

BACKGROUND: Antibody-mediated rejection after ABO-incompatible kidney transplantation (ABO-I KTx) is a major barrier to transplantation success. The advent of immunosuppressive therapy has markedly improved graft survival in ABO-I KTx. However, compared with normal KTx, clinical conditions during ABO-I KTx are difficult to control because of overimmunosuppression. To reduce the need for immunosuppression, we aimed to develop a novel blood group antigen-neutralizing therapy. METHODS: We screened for an ABO blood group antigen-targeting peptide (BATP) by screening of T7 phage-displayed peptide library. After screening, hemagglutination inhibition assays, enzyme-linked immunosorbent assay, and cytotoxicity assay were used to analyze the blood group antigen-blocking effect and toxicity of BATP. We also tested the inhibitory effects on anti-blood group antibody binding in normal human kidney tissues blocked with BATP and excised kidneys perfused ex vivo with BATP. RESULTS: We identified six peptide sequences that efficiently suppressed hemagglutination of red blood cells by anti-ABO blood group antibodies and binding of these antibodies to ABO histo-blood group antigens in kidney tissues. Surprisingly, ex vivo perfusion of BATP in kidneys excised from renal cell carcinoma patients caused significant suppression of anti-blood group antibody binding to antigen and IgG and IgM deposition in renal glomerular capillaries after ABO-I blood reperfusion. CONCLUSIONS: These data indicate that A/B blood group antigens on red blood cells and in kidney tissues may be neutralized by BATP. This approach may enable the development of a novel blood group antigen-neutralizing therapy to overcome the challenges of ABO-I KTx.

[Delayed haemolytic transfusion reaction due to anti-JK1 antibody]. / Accident hémolytique retardé post-transfusionnel par allo-immunisation anti-JK1.

INTRODUCTION: The sensitivity of the detection of irregular antibodies (DIA) is one of the fundamental basis of transfusion safety. The production of alloantibodies is the first cause of adverse events following transfusion. CASE REPORT: We report a 77-year-old woman who was transfused and presented with a delayed haemolytic anemia due to anti-JK1 alloimmunization. This event highlights the limits of DIA performed before a transfusion, the hazard of this specific type of antibody and the difficulties of the diagnosis of haemolytic anaemia. The preventive measures necessary to avoid this undesirable effect are reminded. CONCLUSION: Despite the sensitive routine test method, the anti-JK1 antibodies could be missed. We should keep in mind the possibility of an anaemia due to alloantibodies we confronted to an unexplained haemolytic episode.

The origins, specificity, and potential biological relevance of human anti-IgG hinge autoantibodies.

Human anti-IgG hinge (HAH) autoantibodies constitute a class of immunoglobulins that recognize cryptic epitopes in the hinge region of antibodies exposed after proteolytic cleavage, but do not bind to the intact IgG counterpart. Detailed molecular characterizations of HAH autoantibodies suggest that they are, in some cases, distinct from natural autoantibodies that arise independent of antigenic challenge. Multiple studies have attempted to define the specificity of HAH autoantibodies, which were originally detected as binding to fragments possessing C-terminal amino acid residues exposed in either the upper or lower hinge regions of IgGs. Numerous investigators have provided information on the isotype profiles of the HAH autoantibodies, as well as correlations among protease cleavage patterns and HAH autoantibody reactivity. Several biological functions have been attributed to HAH autoantibodies, ranging from house-cleaning functions to an immunosuppressive role to restoring function to cleaved IgGs. In this review, we discuss both the historic and current literature regarding HAH autoantibodies in terms of their origins, specificity, and proposed biological relevance.

Biliary apotopes and anti-mitochondrial antibodies activate innate immune responses in primary biliary cirrhosis.

UNLABELLED: Our understanding of primary biliary cirrhosis (PBC) has been significantly enhanced by the rigorous dissection of the multilineage T and B cell response against the immunodominant mitochondrial autoantigen, the E2 component of the pyruvate dehydrogenase complex (PDC-E2). PDC-E2 is a ubiquitous protein present in mitochondria of nucleated cells. However, the damage of PBC is confined to small biliary epithelial cells (BECs). We have previously demonstrated that BECs translocate immunologically intact PDC-E2 to apoptotic bodies and create an apotope. To define the significance of this observation, we have studied the ability of biliary or control epithelial apotopes to induce cytokine secretion from mature monocyte-derived macrophages (MDMphis) from either patients with PBC or controls in the presence or absence of anti-mitochondrial antibodies (AMAs). We demonstrate that there is intense inflammatory cytokine production in the presence of the unique triad of BEC apotopes, macrophages from patients with PBC, and AMAs. The cytokine secretion is inhibited by anti-CD16 and is not due to differences in apotope uptake. Moreover, MDMphis from PBC patients cultured with BEC apoptotic bodies in the presence of AMAs markedly increase tumor necrosis factor-related apoptosis-inducing ligand expression. CONCLUSION: These results provide a mechanism for the biliary specificity of PBC, the recurrence of disease after liver transplantation, and the success of ursodiol in treatment. They further emphasize the critical role of the innate immune system in the perpetuation of this autoimmune disease.

HLA class II-like antiidiotypic antibodies from highly sensitized patients inhibit T-cell alloresponses.

The purpose of this study is to identify factors in the sera of highly sensitized (HS) patients (pts) that inhibit T-cell alloresponses. An in vitro assay was used to measure HLA class I and class II-like antiidiotypic antibodies (anti-ids). The stimulation index (SI) was used to measure PBL and T-cell responses to alloantigens. All HS sera (32 pts) and the IgG fraction inhibited PBL and CD4(+) T-cell responses to alloantigens. The SI with HS IgG was 7.9 +/- 1.7 as compared to 31.5 +/- 5.9 with normal IgG (p = 0.0003). In a subset of pts who were transiently sensitized, the SI was 6.6 +/- 1.0 with a high panel reactive antibody (PRA), but when their PRA was zero, the SI was 17.8 +/- 1.3 (p = 0.0000001). Anti-ids were found in 100% of 17 pts with a high PRA. The T-cell inhibitory factors reduced CD4(+) T-cell responses of HS pts to alloantigens in the presence of autologous anti-ids, were MHC restricted and were inactivated by in vitro generated antibodies to HLA class II-like anti-ids. The HLA class II-like anti-id IgG molecules bind to the TCR of CD4(+) T cells and may impair their ability to help in the downregulating antibody response to anti-ids.

Interleukin (IL)-17A stimulates IL-8 secretion, cyclooxygensase-2 expression, and cell proliferation of endometriotic stromal cells.

IL-17A is secreted from Th17 cells, a discovery leading to revision of the mechanism underlying the role of Th1/Th2 in the immune response. Strong evidence suggests that immune responses associated with inflammation are involved in the pathogenesis of endometriosis. In the present study, we first demonstrated that the presence of Th17 cells in peritoneal fluid of endometriotic women by flow cytometric analysis and IL-17A-positive cells in endometriotic tissues by immunohistochemistry. To investigate the role of IL-17A in the development of endometriosis, we then studied the effect of IL-17A on IL-8 production, cyclooxygensase-2 expression, and cell proliferation of cultured endometriotic stromal cells (ESCs). IL-17A enhanced IL-8 secretion from ESCs in a dose-dependent manner. The IL-17A-induced secretion of IL-8 from ESCs was suppressed by anti-IL-17 receptor A antibodies or inhibitors of p38 MAPK, p42/44 MAPK, and stress-activated protein kinase/c-Jun N-terminal kinase. Addition of TNFalpha synergistically increased IL-17A-induced IL-8 secretion from ESCs. IL-17A also enhanced the expression of cyclooxygensase-2 mRNA and proliferation of ESCs. IL-17A may play a role in the development of endometriosis by stimulating inflammatory responses and proliferation of ESCs.

Allergen induces the migration of platelets to lung tissue in allergic asthma.

RATIONALE: Platelets are essential for pulmonary leukocyte recruitment, airway hyperresponsiveness, and bronchial remodeling in animals with allergic inflammation and can be found in bronchoalveolar lavage of sensitized animals. No studies, however, have explored the direct migration of platelets to lungs. OBJECTIVES: To assess whether platelets migrate into lung parenchyma in response to inhaled allergen in ovalbumin-sensitized mice; to assess the role of the FcepsilonRI receptor in this phenomenon; and to evaluate whether platelets from patients with asthma, or from sensitized mice, undergo chemotaxis in vitro in response to relevant antigens. METHODS: Ovalbumin-sensitized wild-type (WT) mice, or FcRgamma(-/-) mice lacking the FcepsilonRIgamma, were challenged with aerosolized allergen and lungs analyzed by platelet-specific immunohistochemistry. In some experiments, mice were depleted of platelets and cross-transfused with either WT or FcRgamma(-/-) platelets to assess the role of platelet FcRgamma(-/-). Chemotaxis of platelets from patients with asthma or from sensitized mice was studied in vitro. MEASUREMENTS AND MAIN RESULTS: Histology of lungs revealed isolated platelets, migrating out of vessels and localizing underneath the airways after allergen challenge in WT but not in FcRgamma(-/-) mice. Platelets from patients with asthma and from sensitized WT mice, but not from sensitized FcRgamma(-/-) mice, migrated in vitro toward the relevant allergen or an anti-IgE. Platelets from normal mice were found to express FcepsilonRIgamma and platelet-bound IgEs were increased in sensitized mice. CONCLUSIONS: Platelets migrate extravascularly in response to a sensitizing allergen via a mechanism dependent on the interaction among allergen, allergen-specific IgE, and the FcepsilonRI, and this may allow them to participate directly in allergic tissue inflammation.

Peptidomimics of antigen are present in variable region of heavy and light chains of anti-idiotypic antibody and function as surrogate antigen for perpetuation of immunological memory.

Peptide antigens composed of relevant B cell and T cell epitopes, capable of inducing protective immune response against the whole pathogen, are potentially safe, alternative vaccine antigens for prevention of wide range of diseases. Here, we show that short peptides derived from internal image sequences of anti-idiotypic antibody (peptidomimics) can function as both B and T cell epitopes and perpetuate antigen specific immunological memory. We have sequenced the variable regions of heavy and light chains of the anti-idiotypic antibody specific to rinderpest virus hemagglutinin protein and predicted T cell epitopes in these sequences by an immuno-informatics approach. We have studied the interaction of these epitopes with MHC class I by in vitro assays and in silico analysis by molecular modeling of the idiopeptide-MHC complexes as well as antigen-derived peptide-MHC complexes. The functional capacity of anti-idiotypic antibody derived peptides to stimulate antigen specific T cells in vitro was tested. The ability of peptidomimics to proliferate the immune splenocytes in vitro was 10 times more when compared with that of a control peptide taken from the constant region of immunoglobulin. Similarly three- to fivefold more amounts of IL-2 and IFN-gamma were secreted by immune splenocytes in response to in vitro re-stimulation with peptidomimics. Further, we have provided evidence for the generation of antibodies against peptidomimics in memory response generated on antigen or anti-idiotypic antibody immunizations. In summary, our experiments suggest that peptidomimics are generated in the body after antigen immunization and may have important roles in vivo in regulating antigen specific immunological memory.

Stimuli that enhance IgA class switching increase histone 3 acetylation at S alpha, but poorly stimulate sequential switching from IgG2b.

Germ-line (GL) alpha transcription can be induced in mouse splenic B cells by LPS and TGF-beta. This stimulation results in approximately 1% IgA+ cells, which can be increased by IL-4, IL-5, and anti-IgD dextran (alpha delta Dex). To determine the mechanism of this increase, we asked whether IgA class switching correlates with acetylation of histone 3 at S alpha, the switch region for IgA. In the presence of the survival factor B lymphocyte stimulator (BLyS), acetylated histone 3 (AcH3) at S alpha was changed little by TGF-beta in LPS-stimulated mouse splenic B cell cultures, despite induction of GL alpha RNA. Compared with BLyS/LPS/TGF-beta alone, treatment with BLyS/LPS/TGF-beta/IL-4/IL-5/alpha delta Dex increased AcH3 at S alpha fourfold, and also increased GL alpha RNA levels more than eightfold. By contrast, IgG2b class switching was optimal in BLyS/LPS/TGF-beta alone, and was suppressed by IL-4/IL-5/alpha delta Dex. Thus, B cell activators that increase IgA class switching do not increase IgG2b class switching. Further investigation showed that in contrast to purified IgM+ cells, IgG2b+ cells switched poorly to IgA in response to BLyS/LPS/TGF-beta/IL-4/IL-5/ +/- alpha delta Dex. These results suggest that IgA class switching is unusual among isotypes in its requirement for multiple B cell activation signals in addition to LPS and the cytokine that initiates the corresponding GL transcription.

[Anti-idiotypic antibodies as a physiological mechanism of inhibition of cofactor-independent antiphospolipid antibody formation].

Antiphospholipid antibodies (APA) and anti-idiotypic antiphospholipid antibodies (AiAPA) were studied in 148 women subjected to IVF. APA (IgG aCL, aPS,) levels in serum have been defined. Sera IgG fraction was also examined for the presence of AiAPA by three different methods: 1) binding of AiAPA with mouse monoclonal cofactor-independent APA (mAPA) immobilized on plate; 2) AiAPA neutralization of human affinity isolated APA and 3) mAPA binding with phospholipids. Significant difference in AiAPA levels between APA+ and APA- women subjected to IVF have been found. The mean level of AiAPA was lower in APA women subjected to IVF than in APA- women from the same group (p < 0.05). IV infusion of Ig decreased the APA level significantly as well as increased the AiAPA level in APA+ women subjected to IVF. Ig application to incubation in vitro results in decrease of APA levels in serum. Results of this study confirmed possibility of AiAPA participation in down regulation of cofactor-independent APA production in women undergoing to IVF.

Anti-idiotype x anti-CD44 bispecific antibodies inhibit invasion of lymphoid organs by B cell lymphoma.

The demonstration that Abs to adhesion molecules can block tumor metastasis suggested their use for therapy. However, such Abs affect nonmalignant cells as well. To circumvent this adverse effect, we proposed the use of bispecific Abs that bind simultaneously to an adhesion receptor and to a tumor-specific Ag. Such bifunctional Abs bind more avidly to tumor cells that coexpress both target Ags than to normal cells. The Id of the surface Ig of malignant B lymphocytes is a tumor-specific Ag. Therefore, we produced bispecific Abs with specificity to the adhesion molecule, CD44, and to an idiotypic determinant of the murine B cell lymphoma, 38C-13. These anti-Id x anti-CD44 bispecific Abs blocked 38C-13 cell adhesion to hyaluronic acid, while not affecting adhesion of Id-negative cells. In vivo studies demonstrated that the bispecific Abs inhibited lymphoma cell dissemination to the lymph nodes, bone marrow, and spleen, and prolonged survival of tumor-bearing mice. Migration of 38C-13 cells to the lymphoid organs was inhibited by the bispecific Abs. Thus, the bispecific Ab-mediated reduction in metastasis resulted, at least in part, from reduced homing to these organs. In contrast to anti-CD44 monospecific Abs, the anti-Id x anti-CD44 bispecific Abs did not affect immune responses such as delayed-type hypersensitivity. Hence, bispecific Abs against adhesion molecules and tumor-specific Ags may selectively block tumor metastasis in a way which may leave at least part of the immune system intact.

The T lymphocyte in food-allergy disorders.

PURPOSE OF REVIEW: While much attention is focused upon the role of IgE antibodies in food-allergy disorders, the T cell remains central to all forms, both IgE and non-IgE-mediated, of food-hypersensitivity responses. This review considers the central role of the T cell in this group of disorders and provides a comprehensive overview of recent studies that elucidate our understanding of the mechanisms involved in the pathogenesis of food allergy in regard to the role of the T cell. RECENT FINDINGS: Recent studies have defined a dynamic process involving T cell homing receptors (e.g. cutaneous lymphocyte antigen) and activation markers in food-hypersensitivity disorders. Modulation of the T-cell responses occurs through the recognition of dominant allergenic epitopes, the elaboration of regulatory cytokines (e.g. transforming growth factor-beta, IL-4, IL-5, tumor necrosis factor-alpha) and the influence of immunomodulatory microbial and environmental agents. The resulting disorders reflect T-cell dysregulation. SUMMARY: Significant recent advances in our understanding of the role of the T cell in food hypersensitivity have been made and will probably contribute to improved diagnostic and treatment methods in the near future.

Repertoire shift in the humoral response to phosphocholine-keyhole limpet hemocyanin: VH somatic mutation in germinal center B cells impairs T15 Ig function.

Phosphocholine (PC) is a naturally occurring Ag common to many pathogenic microorganisms. Early in the primary response to PC conjugated to keyhole limpet hemocyanin (KLH), T15 Id(+) Abs constitute >90% of the serum Ig in BALB/c mice. During the late primary and memory response to PC-protein, a shift in the repertoire occurs and T15 Id(+) Abs lose dominance. In this study, we use immunohistochemistry and single germinal center microdissection to locate T15 Id(+) cells in the spleen in a primary response to PC-KLH. We demonstrate T15 Id(+) B cells and V(H)1-DFL16.1-JH1 and V kappa 22-J kappa 5 rearrangements in germinal centers early in the immune response; thus loss of T15 dominance is not due to lack of T15 cells within germinal centers. One-hundred thirty one V(H)1 and 57 V kappa 22 rearrangements were cloned and sequenced. Thirty four percent of the V(H)1 clones and 37% of the V kappa 22 clones contained somatic mutations indicating participation in the germinal center response. Six variant T15 H clones were expressed with wild-type T15 L chain in vitro. Two of these Abs were defective in secretion providing the first evidence that mutation occurring in vivo can disrupt Ig assembly and secretion. Of the four secretion-competent Abs, two failed to display binding to PC-protein, while the other two displayed altered carrier recognition. These results indicate that somatic mutation of T15 in vivo can result in the loss of binding and secretion, potentially leading to B cell wastage. The failure of T15 to gain affinity enhancing mutations in the face of these detrimental changes may contribute to repertoire shift.

Immunoglobulin superantigen protein L induces IL-4 and IL-13 secretion from human Fc epsilon RI+ cells through interaction with the kappa light chains of IgE.

Peptostreptococcus magnus protein L is a multidomain bacterial surface protein that correlates with virulence. It consists of up to five homologous Ig-binding domains (B1-B5) that interact with the variable domain of Ig kappa L chains. Intact protein L stimulates the synthesis and the release of IL-4 and IL-13 from human basophils in vitro. A protein L fragment covering the Ig-binding domains B1-B4 also induced IL-4 and IL-13 release from basophils. There was an excellent correlation (r(s) = 0.82; p < 0.001) between the maximal percent IL-4 release induced by protein L and that induced by anti-IgE and between intact protein L and the B1-B4 fragment (r(s) = 0.90; p < 0.01). Removal of IgE bound to basophils markedly reduced the IL-4 release induced by anti-IgE, protein L, and B1-B4. Preincubation of basophils with protein L or anti-IgE caused complete cross-desensitization to subsequent challenge with the heterologous stimulus. IgE purified from myeloma patients PS and PP (lambda chains) blocked anti-IgE-induced IL-4 release, but not the releasing activity of protein L. In contrast, IgE purified from myeloma patient ADZ (kappa chains) blocked both anti-IgE- and protein L-induced secretion. Cyclosporin A, but not cyclosporin H, inhibited protein L-induced release of IL-4 and IL-13 from basophils. Thus, protein L acts as a bacterial Ig superantigen to induce the synthesis and release of IL-4 and IL-13 from basophils by interacting with kappa L chains of the IgE isotype.