Steven O. Stapel

Immunoglobulin G4: an odd antibody

Despite its well‐known association with IgE‐mediated allergy, IgG4 antibodies still have several poorly understood characteristics. IgG4 is a very dynamic antibody: the antibody is involved in a continuous process of half‐molecules (i.e. a heavy and attached light‐chain) exchange. This process, also referred to as ‘Fab‐arm exchange’, results usually in asymmetric antibodies with two different antigen‐combining sites. While these antibodies are hetero‐ bivalent, they will behave as monovalent antibodies in most situations. Another aspect of IgG4, still poorly understood, is its tendency to mimic IgG rheumatoid factor (RF) activity by interacting with IgG on a solid support. In contrast to conventional RF, which binds via its variable domains, the activity of IgG4 is located in its constant domains. This is potentially a source of false positives in IgG4 antibody assay results. Because regulation of IgG4 production is dependent on help by T‐helper type 2 (Th2) cells, the IgG4 response is largely restricted to non‐microbial antigens. This Th2‐dependency associates the IgG4 and IgE responses. Another typical feature in the immune regulation of IgG4 is its tendency to appear only after prolonged immunization. In the context of IgE‐mediated allergy, the appearance of IgG4 antibodies is usually associated with a decrease in symptoms. This is likely to be due, at least in part, to an allergen‐blocking effect at the mast cell level and/or at the level of the antigen‐presenting cell (preventing IgE‐facilitated activation of T cells). In addition, the favourable association reflects the enhanced production of IL‐10 and other anti‐inflammatory cytokines, which drive the production of IgG4. While in general, IgG4 is being associated with non‐activating characteristics, in some situations IgG4 antibodies have an association with pathology. Two striking examples are pemphigoid diseases and sclerosing diseases such as autoimmune pancreatitis. The mechanistic basis for the association of IgG4 with these diseases is still enigmatic. However, the association with sclerosing diseases may reflect an excessive production of anti‐inflammatory cytokines triggering an overwhelming expansion of IgG4‐producing plasma cells. The bottom line for allergy diagnosis: IgG4 by itself is unlikely to be a cause of allergic symptoms. In general, the presence of allergen‐specific IgG4 indicates that anti‐inflammatory, tolerance‐inducing mechanisms have been activated. The existence of the IgG4 subclass, its up‐regulation by anti‐inflammatory factors and its own anti‐inflammatory characteristics may help the immune system to dampen inappropriate inflammatory reactions.

An IL-13 promoter polymorphism associated with increased risk of allergic asthma

IL-13 plays a crucial role in the development of allergic asthma by several mechanisms, including induction of IgE antibodies, airway eosinophilia and hyper-reactivity. We previously established a deregulated production of IL-13 by T cells from allergic asthma patients. In this report we describe the identification of a novel IL-13 promoter polymorphism (C to T exchange) at position −1055. The IL-13 −1055 TT genotype is associated with allergic asthma (P = 0.002), altered regulation of IL-13 production (P < 0.002), and increased binding of nuclear proteins to this region. we postulate that the presence of this polymorphism predisposes to the development of allergic asthma.

Anti-infliximab and anti-adalimumab antibodies in relation to response to adalimumab in infliximab switchers and anti-tumour necrosis factor naive patients: a cohort study

Objective To investigate how antibodies against anti-tumour necrosis factor (anti-TNF) agents influence response after switching from infliximab to adalimumab in rheumatoid arthritis (RA). Methods This cohort study consisted of 235 patients with RA, all treated with adalimumab. At baseline 52 patients (22%) had been previously treated with infliximab (‘switchers’), and 183 (78%) were anti-TNF naive. Disease activity (using the 28-joint count Disease Activity Score (DAS28)) and presence of antibodies against infliximab and adalimumab were assessed. Clinical response to adalimumab was compared between switchers and anti-TNF naive patients and their anti-infliximab and anti-adalimumab antibody status. Results After 28 weeks of adalimumab treatment the decrease in DAS28 (ΔDAS28) for the 235 patients was 1.6±1.5 (mean±SD). Anti-adalimumab antibodies were detected in 46 patients (20%). ΔDAS28 was 1.8±1.4 in patients without anti-adalimumab and 0.6±1.3 in patients with anti-adalimumab (p<0.0001). Thirty-three of the 52 switchers (63%) had anti-infliximab antibodies. Patients with anti-infliximab more often developed anti-adalimumab than anti-TNF naive patients (11 (33%) vs 32 (18%); p=0.039). ΔDAS28 was greater for anti-TNF naive patients (1.7±1.5) than for switchers without anti-infliximab antibodies (ΔDAS28=0.9±1.4) (p=0.009). ΔDAS28 for switchers with anti-infliximab was 1.2±1.3 and did not differ significantly from anti-TNF naive patients (p=0.262). Conclusion Switchers with anti-infliximab antibodies more often develop antibodies against adalimumab than anti-TNF naive patients. Response to adalimumab was limited in switchers without anti-infliximab antibodies, which raises the question whether a second anti-TNF treatment should be offered to patients with RA for whom an initial treatment with an anti-TNF blocker fails, in the absence of anti-biological antibodies.

Testing for IgG4 against foods is not recommended as a diagnostic tool: EAACI Task Force Report.

Serological tests for immunoglobulin G4 (IgG4) against foods are persistently promoted for the diagnosis of food‐induced hypersensitivity. Since many patients believe that their symptoms are related to food ingestion without diagnostic confirmation of a causal relationship, tests for food‐specific IgG4 represent a growing market. Testing for blood IgG4 against different foods is performed with large‐scale screening for hundreds of food items by enzyme‐linked immunosorbent assay‐type and radioallergosorbent‐type assays in young children, adolescents and adults. However, many serum samples show positive IgG4 results without corresponding clinical symptoms. These findings, combined with the lack of convincing evidence for histamine‐releasing properties of IgG4 in humans, and lack of any controlled studies on the diagnostic value of IgG4 testing in food allergy, do not provide any basis for the hypothesis that food‐specific IgG4 should be attributed with an effector role in food hypersensitivity. In contrast to the disputed beliefs, IgG4 against foods indicates that the organism has been repeatedly exposed to food components, recognized as foreign proteins by the immune system. Its presence should not be considered as a factor which induces hypersensitivity, but rather as an indicator for immunological tolerance, linked to the activity of regulatory T cells. In conclusion, food‐specific IgG4 does not indicate (imminent) food allergy or intolerance, but rather a physiological response of the immune system after exposition to food components. Therefore, testing of IgG4 to foods is considered as irrelevant for the laboratory work‐up of food allergy or intolerance and should not be performed in case of food‐related complaints.

Allergen‐specific IgG4 in atopic disease

Allergen-specific IgG4 has often been regarded as a two-headed creature: potentially harmful as well as potentially protective. As more is found out about these antibodies, the harmful effects are found to be hard to substantiate, at least in the allergy domain. The protective effects (with respect to allergy) are still debated, but particularly from the field of parasitology the evidence is accumulating that IgG4 does, under certain conditions, effectively interfere with allergen-induced, IgE-mediated, effector-cell triggering; i.e., it acts as a blocking antibody. It should be noted that, with respect to parasite immunity, this tnay be an undesirable effect (32, 36, 44, 45, 69, 70, 105), Particularly, recent research in the regulation of B cells by T cells and T-cell-dependent cytokines helps to explain the similarities and differences between IgE and IgG4. It will be explained that a striking similarity has been found between IgE and IgG4 with respect to the type of antigen that triggers these immune responses. As will be explained in some detail later, it is now clear that this effect is a refiection of the similar T-cell help requirements: TH2type cells need to be activated for both immunoglobulin isotypes. In view of this similarity between IgE and IgG4 with respect to antigen specificity, it was unexpected to find a marked difference in epitope specificity between IgE and IgG4. The consequence of the differences in epitope specificity is that binding of IgG4 antibody does not necessarily interfere very effectively with the binding of IgE antibodies. In this review, we will argue that the level of allergen-specific IgG4 does not accurately refiect the level of protection obtained, because only a fraction of the allergenspecific IgG4 can interfere effectively with IgE binding. The position with respect to the use of IgG4 antibodies to monitor immunotherapy that we will put forward in this review is that this use of lgG4 antibody assays is justifiable, but its value should not be overrated. The reasoning behind this position statement is that conventional immunotherapy depends on the immunologically specific activation or inactivation of allergen-specific T cells. Currently, this means stimulation of TH2 cells, and this process can be monitored conveniently by measuring allergenspecific IgG4. If no IgG4 antibody is induced by conventional immunotherapy, the therapy is likely to have been ineffective in reaching the allergen-specific immune system. A future challenge for immunotherapy might well be to exploit the increasing knowledge about B-cell regulation and devise strategies to stimulate the production of IgG4 antibodies with the correct epitope specificities.

The presence or absence of antibodies to infliximab or adalimumab determines the outcome of switching to etanercept

Objective The aim of this study was to test the hypothesis that the reason for non-response (caused by immunogenicity or not) to a first tumour necrosis factor (TNF) inhibitor defines whether a second TNF inhibitor will be effective. Methods This cohort study consisted of 292 consecutive patients with rheumatoid arthritis (RA), all treated with etanercept. A total of 89 patients (30%) were treated previously with infliximab or adalimumab (‘switchers’), and the remaining 203 (70%) were anti-TNF naive. All switchers were divided into two groups: with and without antibodies against the previous biological. Differences in clinical response to etanercept between switchers with and without antibodies and patients who were anti-TNF naive were assessed after 28 weeks of treatment using changes in Disease Activity Score in 28 joints (DAS28). Results After 28 weeks of treatment, response to etanercept did not differ between patients who were anti-TNF naive and switchers with anti-drug antibodies (ΔDAS28=2.1±1.3 vs ΔDAS28=2.0±1.3; p=0.743). In contrast, switchers without anti-drug antibodies had a diminished response to etanercept treatment compared to patients who were TNF naive (ΔDAS28=1.2±1.3 vs ΔDAS28=2.1±1.3; p=0.001) and switchers with antibodies (ΔDAS28=1.2±1.3 vs ΔDAS28=2.0±1.3; p=0.017). Conclusion Patients with RA with an immunogenic response against a first TNF-blocking agent had a better clinical response to a subsequent TNF blocker compared to patients with RA without anti-drug antibodies. Hence, determining immunogenicity can be helpful in deciding in which patient switching could be beneficial and can be part of a personalised treatment regimen.

Decreased clinical response to infliximab in ankylosing spondylitis is correlated with anti-infliximab formation

Objectives: Correlation of serum trough infliximab levels and antibodies to infliximab (anti-infliximab) with clinical response in ankylosing spondylitis. Methods: In accordance with the international ASsessment in Ankylosing Spondylitis (ASAS) consensus statement, patients were treated with infliximab (5 mg/kg) every 6 weeks after a starting regimen. Preinfusion sera were collected at baseline, 24 and 54 weeks. At every visit, the 20% improvement response (ASAS-20) was assessed and laboratory tests performed. Results: 24 of the 38 (63%) patients fulfilled ASAS-20 response criteria after 24 weeks of treatment and 21 (53%) after 54 weeks. After 54 weeks, 11 (29%) patients showed undetectable serum trough infliximab levels and detectable anti-infliximab; six of these patients developed an infusion reaction. Anti-infliximab was found significantly more often (p = 0.04) in ASAS-20 non-responders compared with responders at week 54. Serum trough infliximab levels were significantly (p<0.0001) lower in patients with (mean 0.02 mg/l) than in those without (12.7 mg/l) anti-infliximab. Conclusions: In ankylosing spondylitis, high levels of serum trough infliximab correlated with a good clinical response. Detection of anti-infliximab within 54 weeks is associated with undetectable serum trough infliximab levels, reduced response to treatment and increased risk of developing an infusion reaction.

Immunogenicity does not influence treatment with etanercept in patients with ankylosing spondylitis.

Background: Immunogenicity, specifically the onset of antibodies against tumour necrosis factor (TNF) blocking agents, seems to play an important role in non-response to treatment with these drugs. Objectives: To assess the relation of clinical response of ankylosing spondylitis (AS) to etanercept with etanercept levels, and the presence of antibodies to etanercept. Methods: Patients with AS were treated with etanercept 25 mg twice weekly, according to the international Assessment in Ankylosing Spondylitis (ASAS) working group consensus statement. Sera were collected at baseline and after 3 and 6 months of treatment. Clinical response was defined as a 50% improvement or as an absolute improvement of 2 points on a (0–10 scale) Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) score. Functional etanercept levels were measured by a newly developed ELISA, measuring the binding of etanercept to TNF. Antibodies against etanercept were measured with a two-site assay and antigen binding test. Clinical data were used to correlate disease activity with serum etanercept levels. Results: In all, 53 consecutive patients were included. After 3 months of treatment 40 patients (76%) fulfilled the response criteria. Mean etanercept levels were 2.7 mg/litre and 3.0 mg/litre after 3 and 6 months respectively. Characteristics and etanercept levels of responders and non-responders were similar. No antibodies to etanercept were detected with any of the assays. Conclusion: Etanercept levels of responders and non-responders were similar and no antibodies to etanercept were detected with any of the assays. This study indicates that etanercept is much less immunogenic compared with the other TNF-blocking agents.

The relationship between RAST and skin test results in patients with asthma or rhinitis: a quantitative study with purified major allergens.

BACKGROUND Study of the relationship between skin test results and IgE antibody levels is seriously hampered by the use of conventional allergen extracts because the precise amount of relevant allergen for each patient is unknown. OBJECTIVE This study was designed to investigate skin reactivity with purified major allergens and to assess the relation with serum levels of IgE antibodies and to determine which additional factors contribute to the skin test result. METHODS We used five purified major allergens (Der p 1, Der p 2, Fel d 1, Lol p 1, and Lol p 5) in skin tests, RASTs, and histamine release tests in 43 multisensitized patients with asthma or rhinitis. RESULTS The differences in biologic activity of the five major allergens at a given level of specific IgE are within one order of magnitude. A significant residual variation remains in the correlation between skin test results and levels of IgE antibodies, which cannot be explained by imprecision of both tests (Pearson log skin test vs log specific IgE: r = 0.46-0.92). With similar levels of specific IgE, the amount of allergen that is required for a positive skin test result may differ by as much as a factor of 100 between patients. The amount of total IgE in serum contributes significantly to the skin test result. High values of total IgE are accompanied by a lower skin reactivity for allergen. Within individuals, allergens that cause skin test results that deviate from the prediction based on IgE antibody level often show a similar deviation in the histamine release test. This indicates that the type of IgE response (i.e., affinity or epitope recognition pattern) contributes significantly to the skin test result. Skin reactivity for histamine does not significantly influence the skin reactions expressed as allergen threshold. However, increased skin reactions with higher allergen dosages depend on histamine reactivity. CONCLUSION The major allergens tested show similar biologic activities. In addition to IgE antibody level, total serum IgE and type of IgE antibody response contribute significantly to the skin test threshold for allergens. Even in a system with purified allergens, IgE antibody levels and skin test results are not interchangeable as an indicator of the degree of allergic sensitization.

Variability of crossreactivity of IgE antibodies to group I and V allergens in eight grass pollen species

Crossreactivity to Dactylis glomerata, Festuca rubra, Phleum pratense, Anthoxanthum odoratum, Secale cereale, Zen mays, and Phragmites communis of IgE antibodies against Lol p I or Lol p V was investigated by means of RAST‐inhibition. Within a group of sera the degree of crossreactivity was demonstrated to be highly variable. Individual sera were not always equally crossreactive to all pollen species. A high degree of crossreactivity for Group I allergens did not necessarily implicate the same for Group V. Group I and Group V representatives were found to be present in all eight species. It was demonstrated that within this group of grass species significant quantitative and qualitative differences exist, with respect to Group I and Group V allergens. Species with a low phylogenetic affinity to Lolium perenne, like Zea mays and Phragmites communis showed a very low degree of reactivity, even when measured with the most crossreactive sera. A higher taxonomic relationship however, did not always implicate a closer antigenic resemblance. Antigenically both allergens from Zea mays are more similar to Lol p I and Lol p V, than the analogues in Secale cereale.