Nonsteroidal anti-inflammatory drug hypersensitivity syndrome: a multicenter study. II. Basophil activation by nonsteroidal anti-inflammatory drugs and its impact on pathogenesis.

BACKGROUND: Patients who are clinically hypersensitive to nonsteroidal anti-inflammatory drugs (NSAIDs) sometimes present basophil activation in vitro, and in 50% of cases a parallel response to release of sulfidoleukotrienes (cellular allergen stimulation test) is observed. These phenomena occur not only in clinically hypersensitive patients, but also in some healthy controls who tolerate NSAIDs. MATERIAL AND METHODS: We studied 16 clinically hypersensitive patients, 22 controls tolerating NSAIDs, and 29 healthy blood donors (clinical NSAID status unknown) using 2 different basophil isolation techniques (buffy coat or plasma leukocytes). RESULTS: In a population of 13 aspirin-tolerant healthy controls and 29 healthy blood donors, basophil activation with aspirin, diclofenac, and naproxen was analyzed at 4 different concentrations. The results in the 2 groups were quite similar in qualitative terms. Choosing a cutoff of 5% and a stimulation index >2, the proportion of positive results increased with the concentration. There were more positive results at all concentrations using the plasma leukocyte technique. CONCLUSIONS: The most important finding of this study is that basophil activation by NSAIDs occurs not only in clinically hypersensitive patients but also, to a very variable extent and on an individual basis, in apparently normal healthy individuals who tolerate NSAIDs. The phenomenon is clearly dose-related, and hypersensitive patients seem to react to lower NSAID concentrations.

Nonsteroidal anti-inflammatory drug hypersensitivity syndrome. A multicenter study. I. Clinical findings and in vitro diagnosis.

BACKGROUND: We present the results obtained from the largest series of in vitro diagnostic tests ever reported in patients with clinically validated hypersensitivity to acetylsalicylic acid (ASA)/nonsteroidal anti-inflammatory drugs (NSAID) compared with various categories of controls tolerating ASA/NSAIDs. This multicenter study, which was performed within the framework of the European Network for Drug Allergy (ENDA) group, showed that the basophil activation test (BAT), particularly when used with the 3 NSAIDs aspirin (ASA), diclofenac (DIC), and naproxen (NAP), allows us to confirm the diagnosis of NSAID hypersensitivity syndrome. The results of the cellular allergen stimulation test (CAST) frequently correlate with those of the BAT, although not always. An unexpected finding was that basophil activation by NSAIDs is not an all-or-nothing phenomenon restricted to clinically hypersensitive patients, but that it also occurs in a dose-related manner in some NSAID-tolerant control individuals.Therefore, NSAID hypersensitivity appears as a shift in the normal pharmacological response to NSAIDs. These findings allow us to formulate a new rational hypothesis about the mechanism of NSAID hypersensitivity syndrome, a mechanism that most authors continue to describe as "unknown." METHODS: We enrolled 152 patients with a history of hypersensitivity to NSAIDs and 136 control participants in 11 different centers between spring 2003 and spring 2006. Flowcytometric BAT was performed. RESULTS: The most noteworthy results of our study were that 57% of 140 patients presented very clear-cut positive BAT results to multiple NSAIDs, and 16% were entirely negative. In about 27% of cases, positive results were obtained with 1 or 2 concentrations of a single NSAID. There is clearly a correlation between the results of BAT and CAST. CONCLUSIONS: BAT seems particularly indicated in patients with a clinical history of NSAID intolerance, and in whom a provocation test is not advisable for ethical, clinical, or other reasons. Clear-cut positive results can be considered as confirming a history of NSAID hypersensitivity, although negative results may not exclude it.

Pharmacovigilance of drug allergy and hypersensitivity using the ENDA-DAHD database and the GALEN platform. The Galenda project.

Nonallergic hypersensitivity and allergic reactions are part of the many different types of adverse drug reactions (ADRs). Databases exist for the collection of ADRs. Spontaneous reporting makes up the core data-generating system of pharmacovigilance, but there is a large under-estimation of allergy/hypersensitivity drug reactions. A specific database is therefore required for drug allergy and hypersensitivity using standard operating procedures (SOPs), as the diagnosis of drug allergy/hypersensitivity is difficult and current pharmacovigilance algorithms are insufficient. Although difficult, the diagnosis of drug allergy/hypersensitivity has been standardized by the European Network for Drug Allergy (ENDA) under the aegis of the European Academy of Allergology and Clinical Immunology and SOPs have been published. Based on ENDA and Global Allergy and Asthma European Network (GA(2)LEN, EU Framework Programme 6) SOPs, a Drug Allergy and Hypersensitivity Database (DAHD((R))) has been established under FileMaker((R)) Pro 9. It is already available online in many different languages and can be accessed using a personal login. GA(2)LEN is a European network of 27 partners (16 countries) and 59 collaborating centres (26 countries), which can coordinate and implement the DAHD across Europe. The GA(2)LEN-ENDA-DAHD platform interacting with a pharmacovigilance network appears to be of great interest for the reporting of allergy/hypersensitivity ADRs in conjunction with other pharmacovigilance instruments.

Cellular tests in the diagnosis of drug hypersensitivity.

The application of flowcytometry in the study of basophil activation for the diagnosis of allergic diseases has given interesting results in recent years. The quantification of basophil activation by flowcytometry has been proven to be a useful tool for the assessment of the immediate-type response to allergens mediated by IgE or by other mechanisms in drug allergic patients. Up to now, most basophil activation test studies reported in the literature have used CD69 or CD203c as markers to quantify basophil activation after antigen-specific stimulation. Some technical variations such as the use of whole blood or isolated leukocytes, the addition of IL-3, the conditions of storage of the blood sample, the time of incubation with allergens and their concentration can affect the results of the basophil activation tests. The basophil activation test is more sensitive and specific than other in vitro diagnostic techniques in drug allergy. In various studies, its sensitivity in allergy to muscle relaxant drugs ranges between 36 and 97.7%, with a specificity around 95%. For betalactam antibiotics, basophil activation test sensitivity is 50% and its specificity 90%. For NSAIDs, sensitivity varies between 66% and 75%; specificity is about 93%. Basophil activation test reproduces in vitro hypersensitivity mechanisms involved in immediate-type allergic reactions, allows the diagnosis of allergic and pseudo-allergic reactions particularly for drugs, which are often not detectable by serological techniques, such as determination of specific IgE.

Diagnostic tests based on human basophils: more potentials and perspectives than pitfalls.

For the diagnosis of allergy, cellular basophil activation tests (BAT), e.g. histamine or sulfidoleukotriene release tests, have long been introduced, but the expression of basophil activation markers such as CD63 and CD203c detected by flow cytometry has attracted more recent attention. A recent opinion paper in this Journal has stressed not only the potential but also the possible pitfalls of flow-cytometric BAT. We have applied clinical validation of various BAT in various ways for several years, and our experience shows that these new technologies have more potentials and perspectives than pitfalls. A comprehensive review of clinically validated studies on allergy to aeroallergens, insect venoms, latex, food allergens and drugs, e.g. myorelaxants, beta-lactams, pyrazolones and non-steroidal anti-inflammatory drugs, as well as chronic urticaria shows clearly that even with different protocols, reproducible and meaningful results can be obtained. Although the available technologies may still be optimized and better standardized, there are no serious reasons to deprive allergic patients of clinically indicated BAT, which can be performed reliably by any laboratory with allergy and flow-cytometric capacity and expertise.

Hypersensitivity to aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs).

Hypersensitivity to aspirin and other non steroidal anti-inflammatory drugs (NSAIDs) manifesting in the airways (rhinosinusitis, polyps, asthma) or in the skin (urticaria, angioedema) is the second most frequent untoward allergic reaction to drugs. Various aspects of this syndrome, such as its clinical features, the cell types and mediators involved, the role of underlying chronic inflammatory processes, the patterns of cross-reactivity between NSAIDs, the major role of sulfidoleukotrienes (LTC4) and of some other mediators such as prostaglandin E2 (PGE2) and C5a are briefly reviewed. It has been assumed for a long time that there were no reliable in vitro tests for that condition and that diagnostic confirmation can only be ascertained by provocation challenge. This appears no longer to be true, since several recent studies using a leukotriene release test (CAST) or a basophil activation test (BAT) on blood basophils, or a combination of both tests, yields positive results (70-75%) in a sizeable number of clinically validated cases, with a high specificity (above 85%). The finding in that syndrome of hyperreactive basophils suggests that the NSAID hypersensitivity syndrome is due to the associated effect of several factors: 1) Localized inflammatory processes causing a non specific cellular hyperreactivity; 2) An abnormal pharmacogenetic reaction to NSAIDs resulting in a hyperproduction of LTC4 and other mediators by activated mast cells, basophils and eosinophils.

Antigen specific quantification of sulfidoleukotrienes in patients allergic to Betalactam antibiotics.

BACKGROUND: After in vitro allergen-specific stimulation, basophils become activated and release sulfidoleukotrienes LTC4, LTD4 and LTE4. This can be detected by means of the CAST assay. We assessed the positivity criteria and the reliability of antigen-specific sulfidoleukotriene production (CAST) in the in vitro diagnosis of betalactam (BL) allergic patients. MATERIAL AND METHODS: We studied a sample of 67 patients (age 48.94 +/- 15.76 years) who had presented with anaphylaxis or urticaria-angioedema within the first 60 minutes after administration of Amoxicillin (54/67), Penicillin G (7/67), Cefuroxime (5/67) or Cefazoline (1/67). All of them had a positive skin test to at least one of the antigenic determinants of Penicillin. As control group 30 adults with negative skin tests who tolerated BL were included. All of them underwent skin tests, oral provocation tests, specific IgE (CAP-FEIA, Pharmacia) and CAST. RESULTS: Positivity criteria were established by means of ROC curves: a sLT release induced by Betalactams of at least 100 pg/ml and greater than or equal to 3 times the basal value. The overall sensitivity of CAST is 47.7% and specificity 83.3%. Sensitivity of specific IgE is 37.8% and specificity 83.3%. CONCLUSIONS: We have established validated positivity criteria for the CAST technique in patients allergic to Betalactams. This technique is a useful in vitro diagnostic method in patients with IgE-mediated allergy to Betalactam antibiotics.

A new combined test with flowcytometric basophil activation and determination of sulfidoleukotrienes is useful for in vitro diagnosis of hypersensitivity to aspirin and other nonsteroidal anti-inflammatory drugs.

BACKGROUND: We assessed whether nonsteroidal anti-inflammatory drugs (NSAIDs) may provoke blood basophil activation in vitro in aspirin- and NSAID-hypersensitive patients, as detected by a flowcytometric technique using the CD63 marker--flowcytometric basophil activation test (FAST) assay--in addition to the sulfidoleukotriene (sLT) release--the cellular allergen stimulation test (CAST). METHODS: Sixty aspirin- and/or NSAID-hypersensitive patients were studied. Thirty control patients without history and negative provocation challenge were also included. The percentage of activated basophils after in vitro stimulation with NSAIDs at 3 different concentrations was evaluated by an anti-CD63 phycoerythrin conjugate (FAST assay) and the amount of sLTs released in the cell supernatant by ELISA (CAST assay). RESULTS: For aspirin, the FAST indicated a sensitivity of 41.7%, a specificity of 100%, a positive predictive value of 100% and a negative predictive value of 99.4%; for paracetamol 11.7 and 100%, for metamizol 15 and 100%, for diclofenac 43.3 and 93.3%, and for naproxen 54.8 and 74.1%. Many patients showed positive tests to more than 1 NSAID. When considering the first 4 NSAIDs, the global sensitivity increased to 66.7%, while the specificity remained at 93.3%. The addition of the CAST results still increased the sensitivity up to 73.3%, but with a decrease of the specificity to 71.4%. CONCLUSIONS: The FAST shows a high percentage of positive reactions, which may reach 60-70% when 4 NSAIDs are tested and even 88% when the test is performed within 1 month of the last clinical drug exposure and reaction. The test has a high specificity above 90%. The addition of sLT determinations yields additional information in a few isolated cases. It is suggested that this test, when properly used, may help avoid some cumbersome and dangerous provocation challenges.

The flow-cytometric determination of basophil activation induced by aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) is useful for in vitro diagnosis of the NSAID hypersensitivity syndrome.

BACKGROUND: Hypersensitivity reactions to non-steroidal anti-inflammatory drugs (NSAIDs), manifested by cutaneous symptoms and/or airway manifestations represent 20-25% of all hypersensitivity reactions to drugs. Today, it is still claimed that no in vitro diagnostic tests exist for that condition and that the only way to confirm the diagnosis is a provocation challenge. OBJECTIVE: The objective of this study was to assess whether NSAIDs may provoke blood basophil activation in vitro in such patients, as detected by a flowcytometric technique. METHODS: Sixty NSAID hypersensitive patients (38 with cutaneous, 20 with airway and two with cutaneous and airway symptoms) and 30 control patients (15 asthmatics) were selected. Their hypersensitivity was confirmed by documented history indicating at least two clinical episodes to two or more different NSAIDs or by positive oral provocation challenge. Isolated buffy coat leukocytes were stimulated in vitro with aspirin, paracetamol, metamizol, diclofenac, and naproxen. The percentage of activated basophils was evaluated by an anti-CD63. RESULTS: Aspirin showed a sensitivity of 43.3%, a specificity of 100%, a positive predictive value of 100% and a negative predictive value of 99.4%. For the other NSAIDs, the sensitivity and specificity values were: for paracetamol 11.7% and 100%, for metamizol 15% and 100%, for diclofenac 43.3% and 93.3% and for naproxen 54.8% and 74.1%. When considering the first four NSAIDs, the global sensitivity raised to 63.3% and specificity to 93.3%. If the number of tests is to be limited for practical reasons, the combination of acetylsalicylic acid and diclofenac at two concentrations yields a sensitivity of 58.3% and a specificity of 93.3%. CONCLUSIONS: Flowcytometric determinations of basophil activation following stimulation with NSAIDs show a high sensitivity (60-70%) with specificity above 90%. So this test may help avoiding some cumbersome and dangerous provocation challenges.

Cellular allergen stimulation test (CAST) 2003, a review.

Specific diagnosis of immediate type allergies, such as rhinoconjunctivis, asthma, urticaria/angioedema and anaphylaxis, particularly when IgE-mediated, traditionally rests on prick and/or intradermal skin tests and, since about 30 years, on the determination of allergen specific IgEs. Some cellular tests, i.e. tests determining the reactivity of blood cells in vitro, particularly basophils, to allergens, have been available for many years. The determination of histamine release has been widely used in allergy pathophysiological research but its routine application in allergy diagnosis has been restricted to few groups. Basophil degranulation, as determined by microscopic examination, was promoted by some groups in the 1980's but has been largely abandoned since around 10 years ago; an alternative cellular test, based on the determination of sulfidoleukotrienes (LTC4, LTD4, LTE4) produced by IL-3 primed basophils stimulated by allergens in vitro, has been proposed. This test became available commercially in 1993 under the name of CAST (Bühlmann Laboratories, Allschwil, Switzerland). The CAST assay has been used in allergy diagnosis in a variety of indications, such as inhalation allergies, allergies to insect venoms, foods, occupational allergens and various drugs. A large number of reports on CAST diagnostic value, however, have been anecdotal. A meta-analysis of validated and well controlled studies encompasses 37 studies, 1614 patients and 1145 controls. This should definitely establish the value of this diagnostic test, particularly in instances where other in vitro or in vivo diagnostic tests are not reliable, such as food or drug allergies, as well as in non-IgE-mediated immediate hypersensitivity reactions. However, a number of questions about the CAST diagnostic assay are still open or have not been systematically explored. This may explain, in addition to the practical limitations inherent to all allergy cellular tests, why CAST has not yet become a very widely used assay worldwide, having gained broad acceptance in some countries but not in others.

Importance of early allergen contact for the development of a sustained immunoglobulin E response in a dog model.

BACKGROUND: Immunoglobulin E (IgE)-mediated allergies are postulated to require early allergen contact and sensitization for the full development of sustained IgE levels. METHODS: Thirty-two Beagle dogs from seven litters selectively bred for their high IgE response were sensitized by subcutaneous injection of chicken ovalbumin (OVA), peanut extract and recombinant birch pollen allergen (Bet v 1). In half of the dogs from each litter, sensitization injections were started on the first day of life; the other half of the same litter was first sensitized at the age of 4 months. To evaluate whether early sensitization also predisposes the animals to IgE responses to other allergens later in life, we injected a recombinant timothy grass pollen allergen (Phl p 5) later on, at the age of 10-12 months. Allergen-specific serum IgE and IgG levels were evaluated with enzyme-linked immunosorbent assays. In addition, 21 dogs were challenged with aerosolized OVA to measure bronchoconstrictive changes in lung function. RESULTS: Early sensitized dogs developed significantly higher OVA-specific serum IgE levels than late sensitized dogs, in contrast to the IgG levels, which were lower in these dogs (p < 0.001). The increase in specific serum IgE and IgG following boosting remained different between the two groups for over a year. Titers of specific serum IgE and IgG were also different after sensitization with a new allergen injected later in life for the first time. Dynamic pulmonary compliance and resistance, both parameters for bronchoconstriction induced by OVA aerosol challenge, were also significantly higher in early sensitized dogs (for both parameters, p < 0.01). CONCLUSIONS: Contact with an allergen early in life is decisive for the development of sustained IgE levels and the development of IgE responses to additional allergens encountered later in life. Allergen avoidance during early life may have some preventive effect on IgE-mediated allergy in dogs.

Use of CD63 expression as a marker of in vitro basophil activation and leukotriene determination in metamizol allergic patients.

BACKGROUND: We assessed the reliability of basophil activation test (FAST) and sulphidoleukotriene production (CAST) in the in vitro diagnosis of allergy to metamizol, evaluating its sensitivity and specificity. METHODS: Twenty-six patients allergic to metamizol and 30 control individuals were studied. Skin tests with metamizol, FAST, and CAST were performed. RESULTS: FAST sensitivity was 42.3% and specificity 100%. The PPV of FAST is 100% and the NPV 99.4%. The likelihood ratio for a positive value cannot be calculated because the specificity is 100% and the likelihood ratio for a negative value is 0.58. CAST sensitivity was 52%, and specificity 90%. The PPV of the test is 5% and the NPV 99.5%. The likelihood ratio for a positive result was 5.2 and that for a negative result 0.53. FAST detects a larger number of cases when patients are studied within the first 6 months after the clinical reaction (chi = 4.2, P = 0.04) than later. Together with skin tests, FAST allowed detection of 69.2% patients allergic to metamizol, the same as CAST 76%. The joint use of the three techniques allowed identification of 76.9% of cases. CONCLUSIONS: FAST and CAST are useful for the diagnosis of allergy to pyrazolones. Its usefulness clearly increases when recent reactions are studied.

Atopic and nonatopic IgE-mediated allergy: a new interpretation of old facts?

Coined 80 years ago, the term 'atopy' to designate a group of diseases associated with IgE and a hereditary background has raised many discussions. In particular, it is difficult to consider as part of an atopic syndrome cases of IgE-mediated allergies to isolated allergens without evidence of a familial inheritance. The postulate expressed in this essay is that in humans we are essentially dealing with an atopic IgE-mediated allergy, which is the equivalent of a genetically determined high IgE response, and with a nonatopic IgE-mediated allergy, which is the equivalent of a low IgE response in mammals and rodents.

Flow cytometric basophil activation test by detection of CD63 expression in patients with immediate-type reactions to betalactam antibiotics.

BACKGROUND: In this study, we used flow cytometry to determine the percentage of activated basophils that expressed the CD63 marker after in vitro stimulation by different betalactam antibiotics. The diagnostic reliability of the technique was assessed, as well as its correlation with specific IgE. METHODS: Fifty-eight patients with clinical allergy to betalactam antibiotics and presenting positive skin tests to at least one of the allergens (minor determinant mixture (MDM), benzylpenicilloyl-polylysine (PPL), penicillin, ampicillin, amoxicillin, cephalosporins) were tested. Thirty subjects non-allergic to betalactams were also studied as controls. The flow assay stimulation test (FAST) uses flow cytometry to determine the percentage of basophils that express CD63 as an activation marker after in vitro stimulation with allergen. Double labelling with monoclonal antibodies anti-CD63-PE and anti-IgE FITC was used. RESULTS: The allergic patients show a statistically greater number of activated basophils than the control subjects, after the incubation of cells with all the betalactams at various concentrations. The sensitivity of the technique is 50%, the specificity 93.3%, the likelihood ratio for a positive value 7.46 and the likelihood ratio for a negative value 0.54. In spite of having a greater sensitivity (37.9%) and specificity (86.7%) than CAP, differences between sensitivity and specificities of both techniques (CAP and FAST) do not reach statistical significance. CONCLUSION: The basophil activation test is a particularly useful technique in the diagnosis of patients with IgE-mediated allergy to betalactams and allows the identification of 50% of patients. Used in conjunction with CAP, it allows the identification of 65.5% of such patients.

Flow cytometric basophil activation test: a review.

Flow cytometry is a technique enabling the analysis of physical and biological characteristics of cells or other biological particles when labeled with antibodies coupled to fluorochromes or other dyes. The basophil activation test (BAT), also called flow-cytometric allergen stimulation test (FAST) [commercially available under the name of Flow CAST (Bühlmann Laboratories) or BASOTEST (Beckton-Dickinson)] is based on the in vitro allergen-induced specific activation of basophils. This assay rests on the demonstration of some membrane protein markers that appear after exposure to the allergen. This paper reviews some of the literature about the use of this technique in the investigation of immediate-type allergies to inhalant allergens, drugs, and foods, as well as our own experience with this diagnostic technique. Flow cytometry is a reliable method for the quantification of basophil activation after allergenic stimulus in vitro and in vivo. It also enables us to detect allergic and pseudoallergic reactions because of other mechanisms than allergen-specific IgE antibodies. Further clinical evaluation of this technique will allow validation and better establishment of its diagnostic value in allergy.

Allergen-induced basophil activation: CD63 cell expression detected by flow cytometry in patients allergic to Dermatophagoides pteronyssinus and Lolium perenne.

BACKGROUND: In this study, we determined by flow cytometry the percentage of basophils activated after in vitro stimulation by allergens and expressing the CD63 marker. The diagnostic reliability of the technique was assessed as well as its correlation with other in vitro diagnostic parameters. METHODS: Fifty-three patients suffering from asthma and/or allergic rhinitis following sensitization to Dermatophagoides pteronyssinus and 51 patients sensitized to Lolium perenne were investigated. Twenty-four atopic patients not sensitive to these allergens and 38 healthy subjects were also selected as controls. The basophil activation test determines the percentage of basophils which express CD63 as an activation marker, by means of flow cytometry, after in vitro stimulation with allergen, using double labelling with monoclonal antibody anti-CD63-PE and anti-IgE-FITC. RESULTS: No differences in basal values (non-activated control) were found between sensitized patients, atopic controls and healthy controls. On the other hand, sensitized patients showed a significantly higher percentage of activated basophils after stimulation by allergens in vitro than both control groups (P < 0.001). We found a significant correlation between skin tests and basophil activation tests (r = 0.72, P < 0.001). We also found a positive and significant correlation between basophil activation tests and histamine release tests (r = 0.80, P < 0.001), allergen-specific sulphidoleukotriene production (r = 0.7, P < 0.001) and the occurrence of serum allergen-specific IgE (r = 0.71, P < 0.001). CONCLUSION: The basophil activation test is a highly reliable technique in the diagnosis of allergy to inhalant allergens. The sensitivity of the basophil activation test was 93.3%, and its specificity 98.4%, when using a cut-off point of 15% activated basophils as positive result.

In vitro IgE but not IgG production of canine peripheral blood B cells is inhibited by CD40 ligation.

The aim of this study was to investigate in vitro IgE induction in peripheral canine B cells. CD21(+) B cells were purified from the peripheral blood of beagle dogs by positive selection via magnetic separation to a purity of >/=95%. Subsequently, proliferation, and IgG and IgE production of canine B cells were investigated after stimulation with human recombinant Interleukin-4 (hrIL-4) and human recombinant Interleukin-2 (hrIL-2) in the presence or absence of CD40L-CD8 fusion protein (CD40L) of mouse origin. We could demonstrate that canine B cells react on hrIL-2 alone by proliferation and IgG production but not by IgE secretion, whereas activation with hrIL-4 induced proliferation and mainly IgE production. Together, both cytokines synergistically increased B cell proliferation as well as IgG and IgE production. We could also show that mouse CD40L induces proliferation of dog B cells, which is further enhanced by addition of hrIL-4. Unexpectedly, CD40L led to a dramatic decrease in the IL-4 mediated IgE secretion (82% inhibition on an average). In contrast, IgG production was not affected significantly by CD40L. The same effects of CD40L were observed when B cells were stimulated by a combination of IL-2 and IL-4 and this inhibition could not be abrogated by increasing the amounts of IL-4. In summary, activation of canine B cells from peripheral blood by hrIL-4 in the presence or absence of hrIL-2 led to marked IgE production that is strongly and in a dose-dependent manner inhibited by CD40L. Stimulation of IgG production is not influenced by CD40L.