Nemolizumab: un innovador tratamiento biológico para el control de la interleuquina 31 (IL-31) clave en la dermatitis atópica y el prurigo nodular / Nemolizumab: An Innovative Biologic Treatment to Control Interleukin 31, a Key Mediator in Atopic Dermatitis and Prurigo Nodularis

La citoquina IL-31 es una neurocitoquina que estimula las neuronas sensoriales relacionadas con el picor, contribuye a la inflamación, la disfunción y remodelación de la barrera epidérmica. Al interrelacionar los sistemas inmunológico y nervioso constituye un factor clave en el tratamiento de dermatitis atópica y del prurigo nodular. Nemolizumab es un anticuerpo monoclonal humanizado que bloquea la subunidad α del receptor de la IL-31 y modula la respuesta neuroinmunitaria, bloquea directamente la señalización del prurito y alivia rápidamente el prurito, controlando la inflamación y reduciendo la gravedad del eccema en dermatitis atópica y las lesiones pruriginosas del prurigo nodular al restaurar la función epitelial y promover la integridad de la barrera cutánea. Este artículo resume la nueva información relacionada con las funciones de la IL-31 y presenta la evidencia y resultados disponibles hasta el momento de los ensayos clínicos de nemolizumab en dermatitis atópica y prurigo nodular (AU)

Interleukin 31 (IL-31) is a neurocytokine that stimulates sensory neurons involved in pruritus. It contributes to skin barrier inflammation, dysfunction, and remodeling. As the immune and nervous systems are interrelated, IL-31 has a key role in the treatment of atopic dermatitis and prurigo nodularis. Nemolizumab is a humanized monoclonal antibody that blocks the α subunit of the IL-31 receptor, modulates the neuroimmune response, and rapidly alleviates itching by directly blocking signaling. It reduces inflammation and lesion severity in atopic dermatitis and prurigo nodularis by restoring epithelial function and promoting skin barrier integrity. This review synthesizes the latest information on the functions of IL-31 and presents the current evidence, including clinical trial results, on the use of nemolizumab in the treatment of atopic dermatitis and prurigo nodularis (AU)

[Translated article] Nemolizumab: An Innovative Biologic Treatment to Control Interleukin 31, a Key Mediator in Atopic Dermatitis and Prurigo Nodularis / Nemolizumab: un innovador tratamiento biológico para el control de la interleuquina 31 (IL-31) clave en la dermatitis atópica y el prurigo nodular

Interleukin 31 (IL-31) is a neurocytokine that stimulates sensory neurons involved in pruritus. It contributes to skin barrier inflammation, dysfunction, and remodeling. As the immune and nervous systems are interrelated, IL-31 has a key role in the treatment of atopic dermatitis and prurigo nodularis. Nemolizumab is a humanized monoclonal antibody that blocks the α subunit of the IL-31 receptor, modulates the neuroimmune response, and rapidly alleviates itching by directly blocking signaling. It reduces inflammation and lesion severity in atopic dermatitis and prurigo nodularis by restoring epithelial function and promoting skin barrier integrity. This review synthesizes the latest information on the functions of IL-31 and presents the current evidence, including clinical trial results, on the use of nemolizumab in the treatment of atopic dermatitis and prurigo nodularis (AU)

La citoquina IL-31 es una neurocitoquina que estimula las neuronas sensoriales relacionadas con el picor, contribuye a la inflamación, la disfunción y remodelación de la barrera epidérmica. Al interrelacionar los sistemas inmunológico y nervioso constituye un factor clave en el tratamiento de dermatitis atópica y del prurigo nodular. Nemolizumab es un anticuerpo monoclonal humanizado que bloquea la subunidad α del receptor de la IL-31 y modula la respuesta neuroinmunitaria, bloquea directamente la señalización del prurito y alivia rápidamente el prurito, controlando la inflamación y reduciendo la gravedad del eccema en dermatitis atópica y las lesiones pruriginosas del prurigo nodular al restaurar la función epitelial y promover la integridad de la barrera cutánea. Este artículo resume la nueva información relacionada con las funciones de la IL-31 y presenta la evidencia y resultados disponibles hasta el momento de los ensayos clínicos de nemolizumab en dermatitis atópica y prurigo nodular (AU)

Nemolizumab: An Innovative Biologic Treatment to Control Interleukin 31, a Key Mediator in Atopic Dermatitis and Prurigo Nodularis. / Nemolizumab: un innovador tratamiento biológico para el control de la interleuquina 31 (IL-31) clave en la dermatitis atópica y el prurigo nodular.

Interleukin 31 (IL-31) is a neurocytokine that stimulates sensory neurons involved in pruritus. It contributes to skin barrier inflammation, dysfunction, and remodeling. As the immune and nervous systems are interrelated, IL-31 has a key role in the treatment of atopic dermatitis and prurigo nodularis. Nemolizumab is a humanized monoclonal antibody that blocks the α subunit of the IL-31 receptor, modulates the neuroimmune response, and rapidly alleviates itching by directly blocking signaling. It reduces inflammation and lesion severity in atopic dermatitis and prurigo nodularis by restoring epithelial function and promoting skin barrier integrity. This review synthesizes the latest information on the functions of IL-31 and presents the current evidence, including clinical trial results, on the use of nemolizumab in the treatment of atopic dermatitis and prurigo nodularis.

Circulating CLA+ T cells in atopic dermatitis and their possible role as peripheral biomarkers.

Cutaneous lymphocyte-associated antigen (CLA+ ) T cells are specialized for skin homing and represent the main T-cell population in atopic dermatitis (AD) lesions. CLA+ is expressed on the surface of circulating CD45RO+ memory T cells and most skin-infiltrating T cells. Mechanistic studies and thus treatment advancements are limited by the need of large number of skin biopsies. Circulating CLA+ T cells may be a reliable surrogate marker of the inflammatory events occurring in the skin, and thus, the evaluation of CLA+ T cells in the blood may eliminate the need for skin biopsies. Preliminary work in AD has established that disease-associated T-cell abnormalities can be approached by either a study of skin lesions or activated CLA+ T-cell subsets in peripheral blood. Future studies in adults and children, across different skin disorders, correlating blood and skin phenotypes and determining skin-homing T-cell functional properties are needed to establish whether CLA+ memory subsets can be used as biomarkers and a substitute for skin biopsies. This review summarizes the latest advancements reached on circulating CLA+ in AD and the great potential they harbor in understanding AD mechanisms.

[Production of interleukin-8 by circulating CLA+ T cells with skin tropism in patients with psoriasis and in healthy controls]. / Producción preferente de IL-8 por linfocitos T CLA+ circulantes con tropismo cutáneo en pacientes con psoriasis y en sujetos sanos.

BACKGROUND: Psoriasis is an immune-mediated disease typically associated with cutaneous neutrophilic infiltration and Munro microabscesses. Interleukin (IL)-8 is one of the main neutrophil-attracting chemokines. Although keratinocytes have traditionally been considered to be the principal source of IL-8 in psoriasis, we present data that suggest that cutaneous lymphocyte associated antigen (CLA) + T lymphocytes synthesize this cytokine. MATERIAL AND METHODS: Six patients with psoriasis and 6 healthy controls were studied. Immunomagnetic separation was used to isolate CLA+ and CLA- T lymphocytes and IL-8 and interferon (IFN)-gamma production was quantified for each cell subpopulation using enzyme-linked immunosorbent assay. Finally, gene expression of IL-8 was analyzed by reverse transcriptase-polymerase chain reaction. RESULTS: CLA+ and CLA- T lymphocytes from patients with psoriasis and from controls showed a significantly increased production of IFN-gamma when activated, whereas only activated CLA+ T lymphocytes (from patients and controls) synthesized IL-8. The higher level of expression of IL-8 and IFN-gamma by CLA+T lymphocytes in comparison to CLA- cells was confirmed. DISCUSSION: Previous studies have confirmed IL-8 production by T lymphocytes in inflammatory skin diseases with neutrophil-rich infiltrates, such as acute generalized exanthematous pustulosis, Behçet disease, and pustular psoriasis. We have confirmed the role of the subset of T lymphocytes with skin tropism (CLA+) in IL-8 production in nonpustular psoriasis.

Calcitonin gene-related peptide modulates interleukin-13 in circulating cutaneous lymphocyte-associated antigen-positive T cells in patients with atopic dermatitis.

BACKGROUND: Neuropeptides (NPs) may play an important role in the pathogenesis of atopic dermatitis (AD) by regulating immune responses and contributing to the cross-talk between the immune and nervous systems. OBJECTIVES: To assess the ability of NPs to influence interleukin (IL)-13 and interferon (IFN)-gamma production and the expression of the activation marker HLA-DR in skin memory T cells [cutaneous lymphocyte-associated antigen (CLA)+ T cells] from patients with AD with severe, chronic lesions and intense pruritus, and from nonatopic controls. METHODS: Cells were cultured in the presence and absence of different NPs, calcitonin gene-related peptide (CGRP), somatostatin (SOM) and substance P (SP). IL-13 and IFN-gamma production and HLA-DR expression were measured in both CLA+ and CLA- T-cell subsets by flow cytometry. RESULTS: CGRP increased IL-13 production in peripheral blood mononuclear cells from patients with AD (P < 0.05), with no changes detected in the presence of SOM or SP. These patients with AD had a lower expression of CGRP receptor compared with controls (P < 0.05). Memory T cells incubated with CGRP also showed an increase in IL-13 (P < 0.05) and HLA-DR (P < 0.05) in CLA+ T cells from patients with AD compared with controls, but not in CLA- T cells. Patients with a higher production of IL-13 were those with higher total IgE and percentage of skin area involved. Furthermore, the IL-13/IFN-gamma ratio was increased in patients with AD after cells were cultured with CGRP (P < 0.05). CONCLUSIONS: Our results suggest an immunomodulatory role of CGRP towards a Th2 pattern in CLA+ T cells, which may contribute to exacerbating clinical symptoms in patients with AD.

[Effector function of CLA(+) T lymphocytes on autologous keratinocytes in psoriasis]. / Función efectora de linfocitos T CLA1 sobre queratinocitos autólogos en psoriasis.

BACKGROUND: Cutaneous lymphocyte antigen (CLA) is expressed by a subgroup of memory T cells that exhibit skin homing and are implicated in cutaneous T-cell-mediated diseases. MATERIAL AND METHODS: Expression of genes associated with psoriasis was analyzed in keratinocytes taken from patients and healthy individuals and cultured under different conditions, including activation using supernatants from CLA(+) T lymphocytes activated with anti-CD3 and anti-CD28 antibodies. RESULTS: Keratinocytes from psoriasis patients activated by CLA(+)T lymphocytes expressed higher levels of interferon-inducible protein 10, HLA-DR, intercellular cell adhesion molecule 1, and inducible nitric oxide synthase. CONCLUSIONS: Our results suggest that we have developed an in vitro model that will allow analysis of the effector role of CLA(+) T lymphocytes on keratinocytes in psoriasis. This model may allow the identification of genes involved in the pathology of psoriasis through induction by CLA(+) T lymphocytes.

Different lymphocyte markers and cytokine expression in peripheral blood mononuclear cells in children with acute atopic dermatitis.

BACKGROUND: The pathogenesis of atopic dermatitis (AD) is still not completely understood. AD is characterized by the presence of clinical symptoms of both IgE antibody-mediated immediate hypersensitivity and specific T lymphocyte-mediated delayed hypersensitivity. OBJECTIVE: To evaluate the immunological mechanisms involved in children with acute AD lesions. MATERIAL AND METHODS: Ten children with acute AD lesions and 10 non-atopic controls were studied. Total IgE was measured by immunoassay. T cell marker expression (CD3, CD4, CD8, cutaneous lymphocyte-associated antigen [CLA]) and cytokine production (interferon [IFN]-gamma, interleukin [IL]-13) were analyzed in peripheral blood mononuclear cells by flow cytometry. RESULTS: In children with AD the percentage of CD3+ cells (p = 0.015) increased while that of CD8+ cells (p = 0.023) decreased, with no differences in CLA expression. We found increased IL-13 production in CD3+ cells (p = 0.01) and CD3+CD4+ (p = 0.001) cells with no difference in IFN-gamma. Total IgE was significantly higher in patients with AD (p = 0.01). Comparison of IL-13 production in CD4+ cells categorized by total IgE level showed that IL-13 production was significantly increased in subjects with a higher IgE level. CONCLUSION: Peripheral blood from children with AD showed an increase in IgE levels and a Th2 pattern. There was a correlation between IL-13 production and total IgE levels.

Different cytokine production and activation marker profiles in circulating cutaneous-lymphocyte-associated antigen T cells from patients with acute or chronic atopic dermatitis.

BACKGROUND: Atopic dermatitis (AD) is an inflammatory skin disease whose lesions can have two stages: acute and chronic. In skin biopsies a biphasic pattern of cytokine expression has been shown, Th2 in acute lesions and Th1 in chronic AD lesions. OBJECTIVE: We investigated the expression of an activation marker and a homing receptor, as well as cytokine production, in different peripheral blood T cell subpopulations from AD patients with chronic (Group A) and acute lesions (Group B) and controls. METHODS: We evaluated 26 adult AD patients (12 Group A, 14 Group B) and 14 non-atopic controls. IgE was measured by immunoassay. CD4, CD8, cutaneous-lymphocyte-associated antigen (CLA) and human leucocyte antigen (HLA)-DR expression, and cytokine production (IL-2, IL-13, IFN-gamma, TNF-alpha, IL-10, IL-4) were analysed in mononuclear cells by flow cytometry. RESULTS: In Group B there was a significant increase in eosinophil levels and a non-significant increase in IgE. In Group A we found an increase in CLA(+)CD4(+) cells (8.19+/-1.84) compared with controls (4.83+/-0.53) (P<0.05) and CD4(+)HLA-DR(+) cells in the CLA(+) subpopulation (45.54+/-15.40) compared with controls (30.49+/-6.07) (P<0.05). In the CLA(+)CD4(+) subpopulation, there was a significant increase in IL-4, IL-13 and TNF-alpha production in Group B (12.46+/-7.7, 11.26+/-5.97, 43.92+/-15.55) compared with controls (5.34+/-3.50, 4.54+/-1.78, 19.29+/-9.97) with no differences in Group A. CONCLUSION: Greater immunological differences were detected in peripheral blood from patients with acute compared with chronic lesions, especially in the circulating T cell-subset with skin tropism that preferentially responded to cutaneous allergens. This is the first demonstration of phenotypic changes in circulating CLA(+) T cells between AD patients with acute and chronic lesions.

IL-4 and IL-13 downregulate rolling adhesion of leukocytes to IL-1 or TNF-alpha-activated endothelial cells by limiting the interval of E-selectin expression.

Leukocyte extravasation is governed by the endothelium, expressing a defined pattern of adhesion molecules in response to inflammatory stimuli. Among them, E-selectin, which is expressed in response to interleukin 1 (IL-1) or tumour necrosis factor alpha (TNF-alpha), provides rolling adhesion of the circulating leukocytes, a transient and reversible interaction that initiates leukocyte extravasation. In our experiments, E-selectin expression culminated after 4 to 6 h and declined thereafter. After 24 h a considerable amount of E-selectin was presented, reflecting its continuous expression in different inflammatory skin disorders. After preincubation of the endothelial cells with TNF-alpha together with IL-4 or IL-13, E-selectin mRNA transcription and protein expression were markedly reduced at 8 h and almost abolished at 20 h. In contrast, early E-selectin expression between 2 to 6 h was not significantly impaired. In a rotating adherence assay that mimics physiological shear forces in circulation, preincubation of the endothelial cells with TNF-alpha for 4 and 20 h induced similar adherence of neutrophils, which was largely E-selectin dependent. According to the modified expression kinetics of E-selectin in the presence of IL-4 of IL-13 rolling adhesion was unimpaired at 4 h but significantly diminished after 20 h of preincubation. Similar results were obtained with clones of the cutaneous T cell lymphoma cell line HUT78 highly expressing the E-selectin ligand cutaneous lymphocyte-associated Ag. Together, these data suggest that IL-4 and IL-13 control the rolling adhesion by limiting the period of the induced E-selectin expression and may thereby confine the acute phase of leukocyte emigration.

The interleukin-8 receptor B and CXC chemokines can mediate transendothelial migration of human skin homing T cells.

We studied the involvement of chemokines that bind to G protein-coupled receptors in the migration of skin homing T cells across a bilayer vascular construct (BVC) consisting of a fibroblast matrix underneath an activated endothelial (EC) monolayer. Based on the expression of the cutaneous lymphocyte-associated antigen (CLA), a skin homing receptor, CD45R0+ T cells freshly isolated from blood or HUT-78 cutaneous T lymphoma cells were separated into CLA+ and CLA- subpopulations. These T cells were incubated on interleukin (IL)-1 beta and tumor necrosis factor-alpha-activated EC, and the number of transmigrated cells was determined. The chemokine IL-8 was selectively involved in the enhanced migration of CLA+ T cells across activated EC as demonstrated by blocking antibody to IL-8 but not to GRO-alpha, MCP-1 and RANTES. Identical results were obtained with both human umbilical vein EC (HUVEC) and microvascular skin EC (HDMEC). Pertussis toxin selectively inhibited the enhanced transendothelial migration (TEM) of CLA+ T cells, suggesting that CLA-dependent TEM depends on Gi protein-transmitted signals. Moreover, the IL-8 receptor B (IL-8RB) appeared to be functionally involved in TEM, as demonstrated by receptor desensitization with the CXC chemokines IL-8 and GRO-alpha and by blocking the IL-8RB with specific monoclonal antibodies. Although only the IL-8RB was involved in CLA-dependent TEM, mRNA encoding IL-8RA and IL-8RB was expressed by both CLA+ and CLA- T cells. This correlated with IL-8RA and IL-8RB surface expression on these cells. Thus, the IL-8RB is selectively functional in TEM of T cells expressing the skin homing receptor CLA. Our results demonstrate a critical role for IL-8 and possibly other IL-8RB ligands in addition to the IL-8RB in TEM and suggest the involvement of these molecules in the homing of specific T cells to inflamed skin.

Circulating allergen-reactive T cells from patients with atopic dermatitis and allergic contact dermatitis express the skin-selective homing receptor, the cutaneous lymphocyte-associated antigen.

The cutaneous lymphocyte-associated antigen (CLA) is the major T cell ligand for the vascular adhesion molecule E-selectin, and it has been proposed to be involved in the selective targeting of memory T cells reactive with skin-associated Ag to cutaneous inflammatory sites. To further investigate the relation of CLA and cutaneous T cell responses, we analyzed the CLA phenotype of circulating memory T cells in patients with allergic contact dermatitis and atopic dermatitis (AD) alone vs in patients manifesting bronchopulmonary atopy (asthma with or without AD) and nonallergic individuals. Significant T cell proliferative responses to Ni, a contact allergen, and to the house dust mite (HDM), an allergen to which sensitization is often observed in AD and/or asthma, was noted only in allergic and atopic individuals, respectively. When the minor circulating CLA+CD3+CD45RO+ subset was separated from the major CLA-CD3+CD45RO+ subpopulation in Ni-sensitive subjects, the Ni-dependent memory T cell response was largely confined to the CLA+ subset. A similar restriction of the T cell proliferative response to the CLA+ memory subset was observed for HDM in patients with AD alone. In HDM-sensitive patients with asthma with or without AD, however, the CLA- subset exhibited a strong antigen-dependent proliferation, in contrast to patients with AD alone, whose CLA- subset proliferated very weakly to HDM. In asthma with or without AD, the HDM-dependent proliferation slightly predominated in the CLA- when compared to the CLA+ subset. The functional linkage between CLA expression and disease-associated T cell effector function in AD was also demonstrated by the finding that the circulating CLA+ T cell subset in AD patients, but not nonatopic controls, selectively showed both evidence of prior activation (human histocompatibility antigen-DR expression) and spontaneous production of interleukin 4 but not interferon-gamma. Taken together, these observations demonstrate the correlation of CLA expression on circulating memory T cells and disease-associated memory T cell responses in cutaneous hypersensitivity, and they suggest the existence of mechanisms capable of sorting particular T cell Ag specificities and lymphokine patterns into homing receptor-defined memory subsets.

Migration of skin-homing T cells across cytokine-activated human endothelial cell layers involves interaction of the cutaneous lymphocyte-associated antigen (CLA), the very late antigen-4 (VLA-4), and the lymphocyte function-associated antigen-1 (LFA-1).

The cutaneous lymphocyte-associated Ag (CLA) is expressed by a subset of circulating memory/effector T cells and by the vast majority of skin-infiltrating T cells. CLA is thought to target skin-associated T cells to inflammatory skin sites by interacting with endothelial cell ligand E-selectin (CD62E). We have examined adhesion molecules involved in the migration of human CLA+ and CLA- memory/effector T lymphocytes through IL-1- and TNF-alpha-activated and nonactivated HUVEC layers under static (nonflow) conditions. CLA-enriched memory/effector T lymphocytes migrated more actively across cytokine-activated HUVEC than CLA-depleted memory/effector T cells. This enhanced migration is dependent on the CLA/E-selectin interaction. mAb to very late Ag-4 (VLA-4) and vascular cell adhesion molecule-1 (VCAM-1) blocked the migration of CLA-enriched, but not of CLA-depleted, T cells across activated HUVEC. The observation that anti-VLA-4 and anti-CLA mAb did not show additional inhibition supports the concept that CLA and VLA-4 are sequentially involved in the extravasation. The fact that only CLA+ T cells were inhibited by the anti-VLA-4 mAb suggests that, in this system, CLA engagement is required for using the VLA-4/VCAM-1 pathway. Our studies demonstrate that CLA+ T cells use LFA-1/intercellular leukocyte adhesion molecule-1 (ICAM-1) for transmigration but that CLA expression is not required for the LFA-1/ICAM-1-dependent transmigration because anti-CD18/CD11a mAbs and anti-ICAM-1 mAbs were able to block T cell migration regardless of the activation state of HUVEC or the CLA expression by T cells. Taken together, our results suggest that CLA has a homing function in conducting the T cell to interact with LFA-1/ICAM-1 and/or VLA-4/VCAM-1; this results in enhanced adhesion and migration across cytokine-activated endothelial cells.

Skin-homing T cells in human cutaneous allergic inflammation.

The cutaneous lymphocyte-associated antigen (CLA) is a carbohydrate epitope present on memory/effector T cells that infiltrate inflamed skin. E-selectin is the ligand for CLA and is induced under inflammation on endothelial cells. CLA was originally postulated as a phenotype marker for skin-associated T cells. We studied the specific in vitro response to skin-associated allergens of CLA+ and CLA-CD45RO+ T cells in atopic dermatitis (AD) and contact dermatitis (CD), which represent two well-characterized T cell-mediated cutaneous allergic inflammations. Whereas CLA+ T cells from AD patients preferentially responded to house dust mite (HDM) and CLA+ T cells from nickel CD patients showed an increased response to nickel, CLA-T cells showed very little response in both cases. In contrast, tetanus toxoid, a systemically acting antigen, induced a proliferative response in both CLA+ and CLA- cells. Interestingly the response to HDM in patients with asthma +/- AD was preferentially found in the CLA- subset indicating the involvement of different homing receptors for mucosal tissues. Moreover, CLA+ T cells showed enhanced migration through activated human umbilical vein endothelial cell monolayers compared to CLA- T cells. The CLA binding to E-selectin is initially responsible for the extravasation that also involves VLA-4/VCAM-1 and LFA-1/ICAM-1 interactions. We have recently identified IL-8 as an endothelial cell-derived chemokine and the IL-8 receptor type B which control CLA+ T cell migration. Such a CLA-mediated migration would localize memory/effector T cells that respond to antigens and reach the body through inflamed skin. Our data support the existence of a regionalization of the immune system and in particular of the skin immune system. It may allow an efficient distribution of the immune defense to different sites of the body.

Human monoclonal or polyclonal antibodies recognize predominantly discontinuous epitopes on bee venom phospholipase A2.

BACKGROUND: Two hybridomas, which secrete human monoclonal antibodies of IgG4 isotype specific for the main bee venom antigen/allergen phospholipase A2, were generated. The antigenic determinants recognized by these antibodies were mapped and compared with the binding sites of murine monoclonal and human polyclonal antibodies raised against the same antigen. METHODS: Two hybridomas were developed by fusing heteromyelomas to Epstein-Barr virus immortalized B cells obtained from beekeepers. The cloned hybridomas were stable and secreted up to 40 mg/L of antibody into the culture supernatant. Phospholipase A2 specificity of the human monoclonal antibodies was confirmed by binding and inhibition ELISA and by Western blot analysis. Epitope mapping on phospholipase A2 was done with the PEPSCAN method and ELISA techniques. RESULTS: The epitopes recognized by the human monoclonal antibodies were shown to be discontinuous and did not contain the sugar residue. Similar results were obtained with polyclonal antibodies of IgG4 isotype (from beekeepers) specific for phospholipase A2, which could also inhibit the binding of the human monoclonal antibodies to phospholipase A2. In contrast, antigen binding of the human monoclonal antibodies could not be inhibited by murine monoclonal antibodies against bee venom phospholipase A2. CONCLUSIONS: The data indicate that the human monoclonal antibodies obtained are representative of a part of the polyclonal immune response to phospholipase A2 from beekeepers and may allow a more precise analysis of the humoral immune response to phospholipase A2 that is associated with protection.