IgE antibodies to allergen components

Transcription

1 IgE antibodies to allergen components NY VERSION 2012 SACHS CHILDREN S SACHSSKA HOSPITAl, BARNSJUKHUSET, Stockholm South SÖDERSJUKHUSET General Hospital The contents of this leaflet are based on the authors own clinical experiences, their own and others research in the area. Anna Asarnoj, Susanne Glaumann, Gunnar Lilja, Caroline Nilsson, Mirja Vetander, Magnus Wickman och Eva Östblom. SJUKHUSBACKEN 10, SE STOCKHOLM, sweden. TEL

2 The diagnosis of allergy has so far been based on case history, skin prick test results or the presence of allergen specific IgE antibodies (IgE abs) in serum, elimination of a specific foodstuff, and when possible oral provocation. The use of quantitative allergen-specific IgE has meant a further improvement of the diagnostics. Since 2007 it is possible to analyze IgE abs to single allergenic proteins (allergen components) from various allergy triggering substances. This is what the concept Molecular Allergology refers to. The individual proteins have been given designations based on the Latin name of the species (e.g. peanut = Ara h from Arachis hypogea) and have been numbered in the order that they have been discovered. To identify the primary specific sensitizing allergen in relation to the cross-reacting one To elucidate the probability that the cross-reactive allergen will only give rise to mild reactions if any, by having knowledge of the degree of homology between the sensitizing allergen and other related allergens acquiring knowledge of the degree of protein stability, i.e. how heat and acid instable the allergen is To have knowledge of how much of the protein there is in the allergy source, i.e. how large the dose will be on a given exposure Figure 1. The concept of Molecular Allergology in allergy diagnostics When investigating allergy to milk, egg, fish, pollen, furred animals and mites we now that the higher the IgE levels, the higher is the probability that the patient will suffer symptoms on exposure to the allergen. For a number of allergens from the vegetable kingdom, such as peanut, soy and wheat, such a clear correlation cannot be seen. This is due to the fact that proteins in these foodstuffs contain allergen components with a similar structure as allergenic proteins in pollens, among others, which may result in serological cross-reactivity.

3 PR-10 is a protein found in plant-based foodstuffs. It is homologous with the main allergen of birch and is also present in the hazel nut allergen as Cor a 1, in the peanut allergen as Ara h 8, and in the soy allergen as Gly m 4. These proteins are so similar to the main allergen in birch pollen that serological cross-reactivity can be expected, especially if the level of IgE to birch is high. As these allergens have similar three-dimensional structures and the same biological function, i.e. the degree of homology is high, also the risk for clinical cross-reactivity increases. This is why individuals allergic to birch pollen experience itching in the mouth and throat when eating plant-based foods containing PR-10 proteins, e.g. apple, peach or hazel nut, and can also react with the same symptoms if they drink a soy beverage or eat peanuts. Individuals allergic to birch pollen reacting to hazel nut, peanut or soy as a result of IgE cross-reactivity with birch are generally not at any significant risk for suffering severe symptoms on ingestion of these food allergens. One condition is, however, that they do not have a primary sensitization to these foodstuffs, i.e. they do not have a true peanut, hazel nut or soy allergy. The reason why serious symptoms do not appear in birch pollen allergic individuals with IgE cross-reactivity with peanut, hazelnut or soy is that the birch pollen homologous allergens are relatively instable. They are denatured by the enzymes and acid of the gastric juice, and on heating. The prerequisite is however that the intake of the allergen in question is not too large or too rapid. The same possibilities for IgE cross-reactivity also exist between a number of other allergens, e.g. between different pollens (birch, grass and mugwort), various furred animals (cat, dog and horse), bee and wasp, latex, avocado and chestnut, mites and cockroach, between all kinds of shellfish and between all beans, nuts and seeds. Since 2007 molecular allergology has been used at Sachs Children s Hospital, in research and in clinical routine for allergy diagnostics. This has considerably simplified the management of allergies, above all food allergies, improved our possibilities to give fact based information to the patient, and reduced the need to prescribe adrenaline in autoinjector to some patient groups. It is important for us to be able to explain to the patient that the presence of IgE abs to an allergen does not necessarily mean that you will get an allergic reaction to the allergen in question. Sometimes unpleasant symptoms may occur due to IgE cross-reactivity, but such a reaction is not to be considered dangerous. This leaflet is not a complete account of the topic of allergy diagnostics using IgE abs to allergen components. For further knowledge we refer to review articles published in recent years (e.g. Hauser M 2010, Sastre J, Clin Exp All 2010, Borres M et al, PAI 2011) and to http//: NOTE! A decreased risk for serious allergic reactions only applies provided that the patient has a birch pollen-related nut, peanut or soy allergy and not a true allergy. Mixed forms exist.

4 ALLERGY DIAGNOSTICS IN FOOD ALLERGY FOOD ALLERGENS FROM THE VEGETABLE KINGDOM Which allergenic proteins from the vegetable kingdom that cause systemic reactions mainly depends on their degree of stability. I foodstuffs from the vegetable kingdom four different protein families can be identified; storage proteins, lipid transfer proteins (LTPs), PR-10 proteins, and profilins. The storage proteins and LTPs are stable and can therefore give rise to systemic reactions. Allergy to LTPs is relatively uncommon in Sweden, despite the fact that LTPs are present in most vegetables, fruits and grains. The reason for this is probably that we are not exposed to pollen containing LTPs. Other stable fruit allergens are various proteases, e.g. cysteine protease which can be found in kiwi (Act d 1). Table 1: The most common protein families in food allergy from the vegetable kingdom Protein family Stability Risk for systemic reaction on ingestion Storage proteins High Yes (2S albumin, 7S globulin, 11S glycin) Lipid transfer proteins High Yes, but rarely in Sweden PR-10 proteins Low, partly low No, but there might be exceptions Profilins Low Never when ingested Peanut - Arachis hypogea Ara h 1 storage protein, 7S glycin Ara h 2 storage protein, 2S albumin Ara h 3 storage protein, 11 S globulin Ara h 6 storage protein, 2S albumin Ara h 8 PR-10 allergen, i.e. Bet v 1 (birch) homolog Ara h 9 lipid transfer protein, LTP When investigating peanut allergy, it might seem sufficient to analyze IgE abs to Ara h 2 ( true ) and Ara h 8 (Bet v 1-homolog) in addition to f13, i.e. peanut allergen extract (for use as a reference). In cases of IgE sensitization to Ara h 2, and above all if the concentration of IgE abs to Ara h 2 is high, IgE abs to Ara h 1 and Ara h 3 are most often positive. IgE abs to Ara h 1 and Ara h 3 demonstrate cross-reactivity to other seeds, beans/peas and tree nuts. Analysis of IgE abs also to Ara h 1 and Ara h 3 may therefore be of value.

5 If there are IgE abs in serum to Ara h 2 and/or Ara h 1/Ara h 3, at a detection limit of 0.35 ku/l, the accuracy of a diagnosis that the patient has a true peanut allergy is more than 97 %. On the other hand, if there are IgE abs only to Ara h 8, more than 99 % tolerate peanuts or experience only mild symptoms from the mouth or throat. The majority of patients with IgE abs to Ara h 2 get symptoms from peanut and it is doubtful if these patients should have to undergo a provocation with peanut in order to confirm the diagnosis. Among patients with IgE abs to Ara h 2 below 2 ku/l there might be a few individuals who tolerate peanut, but there are in fact also those who get severe reactions on provocation. In cases where it is important to establish the degree of severity of reactions to peanut provocation may be considered (e.g. teenage problems with denial). In cases of itching, burning or swelling in the mouth or throat on ingestion of peanuts (like the reaction to apples in birch pollen allergics) sensitization to Ara h 2 cannot be ruled out. You should therefore test these patients for IgE abs not only to Ara h 8, but also to Ara h 2, in addition to peanut f13. The presence of IgE abs to Ara h 9 is linked to allergic systemic reactions, rare in Scandinavia but more common in the Mediterranean countries. Individuals from these countries, but living in Scandinavia, may have IgE abs to Ara h 9. When the sum of IgE abs to Ara h 1-3 and Ara h 8 does not reach the IgE ab level for peanut (f13) sensitization to Ara h 9 can be suspected. Even though we can measure IgE abs to many different peanut components there are individuals who have reactions, despite no positive results for any of the peanut components we know today. IgE ab to peanut (f13) may be elevated, but not to any or only slightly to some of the components we can analyze today. Children/adolescents who are sensitized and have a clinical allergy to peanut, but are eating other nuts and/or almond should be able to continue eating these. There is no scientific evidence that avoiding tree nuts should be recommendable under these circumstances. This is in agreement with our clinical experience in recent years. Summary: In cases of suspected peanut allergy you should above all test for sensitization to peanut (f13), Ara h 2 and Ara h 8. Analyzing IgE abs to Ara h 1 and Ara h 3 should be considered if you wish to obtain a complete picture of the sensitization. In some cases also analysis of IgE abs to Ara h 9 may be needed. Always analyze at the same time for sensitization to birch pollen.

6 Soy Glycine max Gly m 5 storage protein, 7S Globulin Gly m 6 storage protein, 11S Glycin Gly m 4 PR-10, Bet v 1 (birch) homolog In true soy allergy sensitization to Gly m 5 and Gly m 6 is common and the IgE ab levels generally high (>10 ku/l). In patients with IgE abs to peanut that are sensitized to Ara h 1 and/or Ara h 3 the majority also have IgE abs to soybean protein (f14), without suffering reactions to soy. The IgE ab levels to soy are relatively low among patients who are primarily allergic to peanut. Gly m 5 and Ara h 1 are both 7S globulin proteins and Gly m 6 and Ara h 3 are 11S glycin proteins. The homology between peanut and soy 7S globulin is just %, so strong clinical cross-reactions are not to be expected. Soy should not be eliminated from these patients diet unless there is also a clinic soy allergy. Patients with a primary soy allergy often have high levels of IgE abs to soybean (f14) compared to the corresponding level of IgE abs to peanut. Those with a primary peanut allergy often have IgE abs to Gly m 5 and Gly m 6, but the levels are relatively low. There are how ever patients who are primary sensitized to both soy and peanut. They have high IgE ab levels to peanut as well as soy, but such patients are rare. 2S albumin, which is the most important component in the peanut allergen Ara h 2, is also present in soy (Gly m 2S albumin) but studies suggest that Gly m 5 and 6 are the most important allergens in soy for triggering allergic reactions to the foodstuff among children. It cannot be ruled out, however, that Gly m 2S albumin may be more important than we believe. Gly m 2S albumin is currently not commercially available. When an allergic reaction to soy is suspected, above all to soy beverage and with concurrent birch pollen allergy, it is recommended that the IgE abs to the soy component Gly m 4 are analyzed. Gly m 4 is a PR-10 allergen and cross-reacts with birch (Bet v 1). Note that in these patients IgE abs to soybean (f14) may be negative even if IgE abs to Gly m 4 is positive in testing. This is due to the fact that the soybean extract contains just small amounts of Gly m 4. Strong reactions to soy have been traced to sensitization to Gly m 4. This seems to affect birch pollen allergic patients when they drink soy beverages fast and maybe on an empty stomach (e.g. long distance runners or instead of breakfast). This has been observed during the birch pollen season. In some cases systemic reactions have been noted. The explanation may be that Gly m 4 probably is partly heat and acid/enzyme stable. In order for a strong reaction to occur a high dose is probably required. Therefore patients with IgE abs to Gly m 4 do not seem to react to soy flour, provided that the dose of the foodstuff is not high and/or ingested on an empty stomach. The absence of allergy may also be a result of the denaturation of Gly m 4 in the industrial process of producing a soy flour product. Summary: Analyze IgE abs to soy only on suspicion of soy allergy. If the IgE ab level to soybean (f14) is < 0.35 ku/l, but a strong suspicion that soy is involved in the reaction remains, the patient should be tested for IgE abs to Gly m 4 (Bet v 1 homolog) and IgE abs to birch pollen.

7 Hazel nut Corylus avellana Cor a 1 - PR-10, Bet v 1 (birch) homolog Cor a 8 - lipid transfer protein, LTP We are currently lacking some important allergen components in hazel nut, as they are difficult to produce. However, it may get us quite far to analyze IgE abs to Cor a 8 (LTP) and Cor a 1 (Bet v homolog). Sometimes the sum of the IgE ab levels for these two components is significantly lower than the corresponding IgE ab level to hazel nut (f17). The patient then probably has IgE abs to other protein components such as Cor a 9, Cor a 11 and Cor a 14, which are currently not commercially available for analysis. Always test for birch when investigating allergy to hazel nut in order to relate to possible sensitization to Cor a 1. An IgE ab level to Cor a 1 that is higher than the corresponding IgE ab level to hazel nut can in most cases be explained by an even higher IgE ab level to birch pollen. In patients with a primary sensitization to hazel nut a low grade sensitization to walnut is often observed. The clinical relevance of cross-reacting IgE abs to hazel nut and walnut is unknown. Summary: Test for IgE abs to hazel nut (f17) and birch when investigating hazel nut allergy. If f17 and birch are both positive, test for IgE abs to Cor a 1 and Cor a 8. If IgE abs to hazel nut (f17) are present without IgE abs to birch, a primary sensitization to hazel nut can be suspected. If IgE abs to Cor a 1 is negative and IgE abs to Cor a 8 are missing, or if the sum of IgE abs to the hazel nut components do not reach the level of IgE abs to hazel nut (f17), some vital component is missing. These patients may react with severe allergic reactions to hazel nut.

8 in other tree nuts, seeds and leguminous plants (beans/peas) Homologous allergen components such as storage proteins, LTP, PR-10 proteins and some other proteins are found in tree nuts, leguminous plants (peas, beans, lentils) and seeds (sesame, mustard, pumpkin, sunflower, poppy, etc.). Some degree of IgE ab cross-reactivity can therefore be expected. The greater the homology, the higher is the likelihood that clinical cross-reactivity may occur. Table II. Occurrence of 2S albumin, 7S globulin and 11S glycin in peanut and leguminous plants, tree nuts and seeds, and their designations as allergen components Foodstuff PR-10 2S albumin 7S globulin 11S glycin Peanut Ara h 8 Ara h 2, Ara h 6, Ara h 1 Ara h 3 Ara h 7 Soy Gly m 4 Gly 2S albumin Gly m 5 Gly m 6 Pea Pis s 1 Hazel nut Cor a 1 Cor a 14 Cor a 11 Cor a 9 Cashew Ana o 3 Ana o 1 Ana o 2 Pistachio Pis v 1 Pis v 3 Pis v 2, Pis v 5 Walnut Jug r 1 Jug r 2 Jug r 4 Para nut Ber e 1 Ber e 2 Sesame Ses i 1, Ses i 2 Ses i 3 Ses i 6, Ses i 7 Mustard seed Sin a 1 Sin a 2 In cases with clinical symptoms and IgE abs only to tree nuts but not to peanut there is no reason to warn against peanut if the child has previously eaten peanut and tolerated it. If a child has reacted to one kind of tree nut, but tolerates other tree nuts, it can continue to eat these nuts. The same applies to different kinds of leguminous plants, see Figure 2. Figure 2. The degree of sequence homology (0-100 %) between different 7S globulins in allergens in leguminous plants and hazel nut Soy 7S Peanut 7S Pea 7S Hazelnut 7S Gly m 5 Ara h 1 Pis s 1 Cor a 11 Soy 7S % 40-49% 51-56% 31-34% Peanut 7S 40-49% % 43-52% 33-34% Pea 7S 51-56% 43-52% % 35-36% Hazelnut 7 S 31-34% 33-34% 35-36% 100% From Kroghsbo S et al Int Arch Allergy Immunol 2011;155:

9 If an individual reacts to several kinds of nuts, or if the family has great worries concerning a more general nut allergy, you should analyze IgE abs to all nuts, peanut and possible also sesame. It is the pattern of IgE abs to tree nuts and peanut and possibly some seeds like sesame that should be evaluated. In some cases you need to decide if a provocation is needed in order to clarify which nuts that the child tolerates. In cases of high IgE ab levels to a nut that the patient gets allergic reactions to, IgE abs to other nuts are often detected, but at considerably lower levels. This does not necessarily have clinical relevance, especially if the difference in IgE concentration is 10 times or more. The cause is serological cross-reactivity. There is strong IgE ab cross-reactivity between cashew and pistachio. If there is allergy/ sensitization to one of these tree nuts IgE abs to the other need not to be analyzed. Both nuts should be avoided if the individual gets allergic reactions to either pistachio nut or cashew nut. There is also strong IgE ab cross-reactivity between walnut and pecan nut. The same recommendation applies to these two tree nuts as to cashew and pistachio nuts. Among other tree nuts IgE abs to components in paranut can be analyzed. If microarray technology (ISAC) is used, additional tree nut components are available for IgE ab analysis. Wheat Triticum aestivum Tri a 19 - ω--5 gliadin Clinical allergy to wheat is uncommon, but IgE ab sensitization to wheat without allergic symptoms from wheat is much more so. ω-5 gliadin (Tri a 19) is a good marker for clinical wheat allergy, but far from covering all. In the future we will have access to more wheat components. There is good correlation between the presence of IgE abs to the wheat component ω-5 gliadin and the probability of reactions with allergic symptoms to wheat. We recommend testing for IgE sensitization to ω-5 gliadin if the patient has reacted to food where wheat has been ingested a few hours before the occurrence of symptoms. This applies especially to the cases where the analysis of IgE abs to wheat (f4) is negative. Also remember that ω-5 gliadin may be the triggering agent in exercise-induced anaphylaxis. IgE abs to wheat (f4) may be negative in these patients. There is a pronounced IgE ab cross-reactivity between different grains, and between grains and grasses. Just as in the case of nuts, leguminous plants and seeds, the grains contain homologous allergens. This also applies to corn and rice, even if allergy to these two foodstuffs is very rare in our part of the world. Summary: In cases of IgE sensitization to wheat (f4) and/or suspected allergy to wheat IgE abs to ω-5 gliadin can be helpful to diagnose wheat allergy. We probably still lack some important wheat components and our knowledge is therefore limited.

10 Allergens in fruits and vegetables Practically all fruits and vegetables contain LTP and profilin. Many also contain PR-10 allergens, i.e. birch pollen homologous allergens. In addition there are enzymatic allergen components that can cause systemic reactions as these allergens are heat and acid stable. LTP is heat and acid stable, whereas PR-10 allergens and profilins are heat and acid unstable. One exception, however, is celery-profilin (Api g 4). Those who react to some fruits and vegetables in raw form but tolerate them in prepared form usually have a PR-10 allergy due to an underlying birch pollen allergy (e.g. raw potato and carrot), while patients who react to cooked, oven-prepared, pasteurized juices may be LTP-allergic. LTP from fruit and vegetables display limited homology. It is uncertain if sensitization to profilin in foodstuffs cause symptoms at all, with the exception of profilin in celery. Mucous contact, e.g. via the airways, peritoneum, rectum or vagina, with profilin, e.g. in pollen if inhaled or latex in contact with the peritoneum, that has not been heated/ denatured can give rise to symptoms. The PR-10 allergen from apple (Mal d 1), LTP from peach (Pru p 3) and profilin from birch (Bet v 2) or peach (Pru p 4) have proved to be good markers for the respective group of allergen components. Mal d 1 can only be analyzed with microarray technology (ISAC). Peach Prunus persica Pru p 1 PR-10, Bet v 1 (birch) homolog Pru p 3 LTP Pru p 4 profilin In the Mediterranean area IgE-sensitization to Pru p 3 is common among persons with systemic reactions to fruit, even if it is ingested in prepared form. It is believed that the allergic reaction to peach may be the result of a primary sensitization to parietaria, olive or platanus trees, the allergens of which all contain LTP. Among patients allergic to birch/ alder/hazel pollen, symptoms in the mouth or throat are common from pome fruits and stone fruits. In middle and northern Europe these reactions are mainly caused by allergens that are homologous with allergens in pollen from birch, alder and hazel, so-called PR-10 proteins. In peach this allergen is designated Pru p 1. PR-10 allergens are, as previously noted, heat and enzyme instable, i.e. they do not withstand heating and they are denatured by the gastric acid. Sensitization to these allergens generally causes only local symptoms in the mouth and throat. If IgE abs to Pru p 3 are analyzed, it is recommended to always simultaneously analyze the amount of IgE abs to Pru p 1. If IgE abs to Pru p 3 is negative, but there are IgE abs to Pru p 1 the suffering of e.g. breathing difficulties at the ingestion of PR-10 allergen-containing fruit can probably be explained by a pronounced oral allergy syndrome in the form of a mild mucosal swelling in the throat which is unpleasant, but not harmful.

11 Kiwi - Actinidia deliciosa Act d 1 - cysteine protease protein Act d 8 - Bet v 1 (birch) homolog It is common that patients with birch pollen allergy react with itching and swelling in the mouth at ingestion of kiwi, but there are also those who may react to the food with anaphylaxis. In birch pollen allergy IgE abs to Act d 8 are elevated. In true kiwi allergy the level of IgE abs to Act d 1 is normally elevated. If IgE abs to Act d 1 is negative, but positive to Act d 8, the suffering of e.g. breathing difficulties at the ingestion of kiwi can probably be explained by a mild mucosal swelling in the throat.

12 FOOD ALLERGENS FROM THE ANIMAL KINGDOM Milk - Bos domesticus Bos d 4 α-lactalbumin Bos d 5 β-lactglobulin Bos d 6 serum albumin Bos d 8 - casein Bos d lactoferrin transferrin We have limited knowledge of the clinical usefulness of components as a diagnostic tool in the investigation of cow s milk allergy. IgE abs to casein, Bos d 8, followed by IgE abs to α-lactalbumin and β-lactglobulin (Bos d 4 and d5) best reflect clinical milk allergy. The vast majority of our patients with severe milk allergy have high IgE ab levels to casein. So far we have only seen a few milk allergic persons who have IgE abs to α-lactalbumin or β-lactglobulin without an elevated IgE level to casein. There is uncertainty concerning the serum albumin in milk and its clinical significance as an allergen. There are reports that individuals allergic to furred animals, who often have IgE abs to serum albumin to furred animals, may have cross-reacting IgE abs to Bos d 6, i.e. milk serum albumin. This cross-reactivity probably lacks clinical significance. Summary: There is more uncertainty concerning the significance of component diagnostics relating to milk than to allergens from the vegetable kingdom, as the IgE cross-reactivity is much less pronounced. This is probably due to our consumption pattern practically all the milk we drink is cow s milk. Egg - Gallus domesticus Gal d 1 - ovomucoid Gal d 2 - ovalbumin Gal d 3 - conalbumin Gal d 4 lysozyme In a published study from Japan with a selected patient material it can be seen that if the individual has an IgE ab level below1.2 ku/l for ovomucoid (Gal d 1), the probability is 95 % or more that the child tolerates egg in prepared (heated) form. Similar data has been in shown in the US. It can also be seen that the IgE-levels for egg and ovomucoid largely follow each other. If these data are transferable to Swedish conditions is not clear. In a situation where provocation may be considered it may however be of value to check the IgE-level to ovomucoid. In those cases when the egg sensitization can be traced to Gal d 2 (ovalbumin) egg is often tolerated in cooked (heated) form. Summary: Consider analysis of IgE abs to ovomucoid, above all in cases with low IgElevels to egg, or when oral provocation is considered and if this provocation could be performed in the patient s home. However, it is the previous case history, i.e. the severity of the symptoms at previous reactions that is most important to evaluate.

13 Meat (cattle, lamb, pig and game) Kött (Nöt, lamm, gris och vilt) α gal It has recently been shown that systemic reactions such as anaphylaxis, generalized urticaria and facial oedema may occur 3 to 6 hours after ingestion of raw meat. The allergy triggering component has been galactose, α-1.3-galactose (α-gal). The epitope α-gal is already well known and is found in tissues in mammals and parasites. According to the literature these patients have often been bit by a tick a few weeks or months before the reaction to meat. This has now been described from the US as well as Europe, including Sweden. It is primarily adults who are affected, but this form of allergy also occurs among teenagers. The patient group is also sensitized to meat from mammals (cattle, pig, lamb, rabbit and game) but not to poultry. A clinically irrelevant sensitization to furred animals (cat, dog, etc.) also occurs among these patients. Fish Gad c 1 parvalbumin from cod Cyp c 1 - parvalbumin from carp The allergen extract for fish is made from cod muscle (f3). Parvalbumin (f426) is the main allergen of cod and also the main allergen in a number of other fish species. There is crossreactivity between different fish species, not least among salt water fish. Different fish have different amounts of parvalbumin. Tuna fish contains small amounts of parvalbumin compared to cod. Parvalbumin from different fish is very similar and recombinant carp parvalbumin contains 70 % of the IgE-binding epitopes present in cod, tuna and salmon. Therefore f3 takes us far in the diagnosis of suspected fish allergy. The experiences of using allergen components in the investigation of fish allergy are so far limited. Summary: In cases of suspected fish allergy, start testing with standard fish extract, i.e. f3. Shellfish Pen a 1 - Tropomyosin from shrimp Tropomyosin is a muscle protein present in various shellfish, clams, octopus, cockroach, mite, anisakis, snails and other parasites. There is IgE ab cross-reactivity for tropomyosin between these species. Between shrimp, crab and lobster the homology is 90 %. In cases of primary sensitization to e.g. shrimp the IgE ab levels for crab, lobster and crayfish should be at almost the same level as IgE for shrimp. The homology between shellfish and clams is only %. Between shrimp and mite the homology is 80 %. It is therefore not surprising if persons with a primary mite allergy are also sensitized to shrimp and other shellfish. The clinical relevance of cross-reactivity between different shellfish is unclear. Summary: Tropomyosin is a muscle protein allergen present in shellfish and molluscs, some arachnea and parasites. Patients allergic to shrimp, crab, lobster or crayfish in most cases tolerate different kinds of clams or octopus.

14 Allergy diagnostics in connection with exercise-induced or idiopathic anaphylaxis VIn cases of anaphylaxis with or without exercise where the cause is unknown an analysis of IgE abs to allergen components from wheat and soy should be made, even if the IgElevels for the whole allergen (wheat or soy) is under 0.35 ku/l. Also investigate the possibility of an underlying allergy to celery or meat (α-gal): Analysis of IgE abs to 1. ω-5 gliadin (wheat component), especially if specific IgE abs to wheat is < 0.35 ku/l and wheat cannot be ruled out as the allergy-causing agent. 2. Gly m 4 (soy component), even if specific IgE abs to soy is < 0.35 ku/l, simultaneously analyze also IgE abs to birch pollen. 3. Celery, also analyze IgE abs to mugwort pollen. 4. IgE abs to α-gal. Summary and some good to know facts IgE ab cross-reactivity is common. Cross-reactions under laboratory conditions: Ara h 2 with several beans/peas, tree nuts and seeds. Ara h 1 with Gly m 5 and several beans/peas, tree nuts and seeds. Ara h 3 with Gly m 6 and several beans/peas, tree nuts and seeds. Tree nuts, seeds, peas and beans often IgE cross-react with each other due to homology, as the allergens contain related proteins (2S albumin, 7S globulin, 11S glycin. LTP, oleosin and profilin). There are probably additional possibilities for cross-reactions under laboratory conditions, but we have limited knowledge of the clinical significance of these connections. Do not test with peanut, hazel nut, soy or wheat in the SPT panel as screening. This only causes problems due to IgE ab cross-reactivity between allergen components in pollen and in various foods. Only test for the food allergen(s) that are suspected based on the case history. If a child eats some nuts but reacts to another nut, it may be valuable to analyze for all nuts, i.e. almond, hazel nut, pecan nut, pistachio, paranut, walnut and cashew. Otherwise you may find yourself in an awkward position in terms of information to the patients. It is easy to forbid all nuts, some of them quite unnecessarily. When analyzing IgE abs to hazel nut and peanut also IgE abs to birch pollen should be analyzed. If the quotient between IgE abs to peanut and birch pollen is > 1, i.e. a higher level of IgE abs to peanut than to birch pollen, you should suspect true peanut allergy. The same applies to sensitization to hazel nut. NOTE that the opposite, i.e. a quotient < 1, is no guarantee that true nut or peanut allergy is not at hand.

15 If the sum of IgE abs to the components analyzed is lower than the IgE abs to the extract, you should be careful, as some components are probably missing in the analysis. The IgE-levels to pistachio and cashew nut correlate, i.e. the content of IgE abs are often at the same level. If sensitization and clinical reaction is present to one of these two nuts you should be careful with the other one until we know more about the connection (clinically and serologically) between the two tree nuts. The same applies to walnut and pecan nut. In small children IgE-levels between ku/l can be seen at anaphylaxis. When the patient is no longer exposed to peanut/tree nuts the IgE ab levels decrease, sometimes by 50 % or more. Values below 0.35 ku/l can therefore be seen at follow-up if the child has not been exposed to the allergen for a time. These children should not be provoked until at least 5 years after the latest exposure (not scientifically proven). Great caution with provocation should be observed if the patient has previously reacted to the food with anaphylaxis of degree 2 or more. A food reaction may occur regardless of test results, even though the risk for a reaction is linked to the IgE ab level. Always take previous reactions into consideration before a possible provocation. Coconut, sunflower seed, pine nuts and sesame are not related to tree nuts and can in most cases be eaten despite simultaneous nut allergy. There are exceptions, however, as these foodstuffs have some allergen components in common. Many children tolerate almond despite allergy to peanut or other tree nuts. They can therefore eat almond paste. Our knowledge of macadamia nuts are limited, but they should be treated as other nuts and they can be tested for.

16 All the authors work at the Sachs Children and Youth Hospital, Stockholm South General Hospital, except Anna Asarnoj who works at Astrid Lindgren Children s Hospital, Karolinska University Hospital, Solna. Contact: magnus.wickman@ki.se Copyright 2012 Anna Asarnoj, Susanne Glaumann, Gunnar Lilja, Caroline Nilsson, Mirja Vetander, Magnus Wickman och Eva Östblom.