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The gelatin story
Editorial The gelatin story
In July of 1991, I saw a 17-year-old woman in consultation because of an adverse reaction to measles, mumps, and rubella (MMR) vaccine. Within 5 minutes of receiving the vaccination, profuse rhinorrhea, total body itching and hives, lightheadedness, and a sensation of throat swelling had developed. She returned immediately to the clinic that had given her the immunization, where her blood pressure was recorded as 70/50, and she was treated appropriately with an injection of epinephrine. After treatment with diphenhydramine and a second dose of epinephrine, her symptoms eventually resolved. When later describing this vaccine reaction, she volunteered that the throat swelling was “kind of like what happens when I eat Jell-O.” She stated that whenever she ate gelatin, within a few minutes she would develop itching and swelling of her throat. Although I had never heard of allergy to gelatin, her history seemed quite convincing. Furthermore, a quick check of the Physicians’ Desk Reference1 revealed that MMR vaccine contains “hydrolyzed gelatin” as a “stabilizer.” Thus it seemed conceivable that her anaphylactic reaction to the vaccine was due to allergy to gelatin. Subsequent skin testing, immunoassays for IgE antibodies, inhibition immunoassays, and protein immunoblotting confirmed that the only component of the vaccine to which the patient made IgE antibody was indeed the gelatin.2 Allergic reactions to MMR vaccine had been thought most likely related to egg allergy.3 However, a review of the literature to date in 1993 (when this case was published) revealed that only 2 of 28 previous reports of anaphylactic reactions to measles or MMR vaccines were in subjects allergic to eggs, whereas literally hundreds of children allergic to eggs had received the vaccines uneventfully.2 This cast serious doubt on any relationship between egg allergy and adverse reactions to these vaccines. On the basis of this single case report,2 astute investi-
From the Department of Internal Medicine (Allergy Division), Naval Medical Center, San Diego. The views expressed in this article are those of the author and do not reflect the official policy or position of the Department of the Navy, Department of Defense, or the US Government. Received for publication Nov 2, 1998; accepted for publication Nov 4, 1998 Reprint requests: CDR John M. Kelso, MC, USN, c/o Clinical Research Department, Naval Medical Center, San Diego, CA 92134-5000. J Allergy Clin Immunol 1999;103:200-2. 1/1/95632
200
Abbreviations used DTaP: Diphtheria, tetanus, and acellular pertussis MMR: Measles, mumps, and rubella
gators in Japan set out to determine whether anaphylactic reactions to measles and mumps vaccines reported in 26 children there might also be due to gelatin.4 Twentysix age- and sex-matched children who had received the vaccines without allergic reactions served as control subjects. The researchers determined that 24 of the 26 children with immediate-type systemic allergic reactions to the vaccines (urticaria, wheezing, and hypotension) had IgE antibody to gelatin, whereas none of the control subjects produced such antibody. Furthermore, they discovered that 7 of the children had a history of hives after eating gelatin, and that in 5 of these 7, the clinical allergy to eating gelatin did not develop until after the vaccine reaction. Similarly, with varicella vaccine, 3 of 4 children with anaphylactic reactions to the vaccine were found to have anti-gelatin IgE, whereas none of 50 control subjects had such antibodies.5 These studies suggested that immediate-type allergic reactions to gelatin-containing vaccines are most often due to allergy to gelatin. A subsequent report examined cellular immune responses in children with both immediate and delayed adverse reactions to MMR and varicella vaccines.6 As with the earlier studies, 6 of 6 patients with histories of immediate-type allergic reactions had anti-gelatin IgE. Also studied were 21 patients with histories of delayed adverse reactions to the vaccines, either redness and swelling at the injection site or a nonurticarial rash that developed several to 48 hours after the immunizations. None of the 21 had anti-gelatin IgE. Specific cellular immune responsiveness to gelatin was studied by in vitro lymphocyte proliferation assay and antigen-specific IL-2 responsiveness. The results of one or both of these assays was positive in all 6 of the patients with immediate reactions and in 17 of the 21 patients with delayed reactions. The tests were negative in 14 control subjects, who had no adverse reaction to the vaccines. This report suggested that lymphocyte responses were involved in both immediate- and delayed-type reactions to gelatincontaining vaccines. Three articles appear in this issue of The Journal that add to the gelatin story. First, Ohsaki et al7 further define T-cell responses in subjects’ reactions to gelatin-containing
J ALLERGY CLIN IMMUNOL VOLUME 103, NUMBER 2, PART 1
vaccines. As might be expected, among 8 subjects with a history of immediate-type allergic reactions to the vaccines and positive test responses for anti-gelatin IgE, incubation of PBMCs with gelatin induced production of mRNA for IL-4, IL-13, or both, which is consistent with a TH2-type response. By contrast, among 8 subjects with delayed reactions to the vaccines, none had any induction of IL-4 mRNA, and 4 had low-level induction of IL-13 mRNA. The picture with the so-called TH1 cytokines, IFN-γ and IL-2, was less clear. All subjects with immediate-type reactions also had robust induction of mRNA for one or both of these cytokines, whereas only 3 of the 8 subjects with delayed reactions had such responses. These 3 were among the 4 who also had induction of IL-13 mRNA. This heterogeneity of responses in subjects with delayed reactions may well reflect that this is a heterogeneous group of patients. Some reactions, such as local redness and swelling, may not be immune mediated at all. No mRNA for these cytokines could be induced in 6 control subjects without any history of adverse reaction to the vaccines. This study further supports and defines the role of TH2 cytokine–driven, IgE-mediated responses to gelatin as important in immediate allergic reactions to gelatin-containing vaccines. As to the TH1 responses, the title of a recent editorial in The Journal says it best, “TH1/TH2 lymphocytes: doubt some more.”8 One question raised by gelatin-related allergic reactions to vaccines is as follows: How did the subjects become sensitized to gelatin in the first place? As above, clinical allergy to the ingestion of gelatin may or may not be present in patients who have allergic reactions to the systemic injection of gelatin.4 Reactions to a gelatin-containing vaccine may occur after the first dose of vaccine because of prior exposure to (and sensitization from) gelatin in other medications or vaccines or by ingestion of gelatin-containing foods. The second article, by Nakayama et al,9 addresses this question. From 1989 to 1993 in Japan, a trivalent MMR vaccine was administered, followed by a series of diphtheria, tetanus, and acellular pertussis (DTaP) vaccines. During this time, no anaphylactic reactions to MMR vaccines were reported. Since 1994, the DTaP series has been given before monovalent MMR vaccines. Since this change in vaccine schedule, numerous reports of anaphylactic reactions to the MMR vaccines have been received. Both the trivalent and the monovalent MMR vaccines contain the same 0.2% gelatin added as a stabilizer; however, only some brands of DTaP vaccine contain gelatin. Among the subjects reported with adverse reactions, almost all had received gelatin-containing DTaP. Thus prior injection with gelatin-containing DTaP vaccine may be the cause of sensitization to gelatin and the subsequent reaction to other gelatin-containing vaccines. In the third article, Sakaguchi et al10 describe how another route of gelatin-containing medication administration can cause anaphylaxis. A patient had anaphylaxis when administered intravenous epoetin (recombinant erythropoietin) that contained gelatin but tolerated anoth-
Editorial 201
er epoetin product without gelatin. She had anti-gelatin IgE but not antiepoetin IgE, implicating gelatin allergy as the cause of her allergic reactions. A number of intravenous gelatin solutions are used as plasma expanders in Europe.11 Anaphylactic reactions have been reported in association with the infusion of these products,12,13 including 2 fatalities.13,14 Some patients who have had such reactions have had positive skin test responses to the gelatin solutions.12,15,16 Thus intravenous gelatin may also induce allergic reactions to gelatin. An electronic search of the 1998 Physicians’ Desk Reference,17 revealed 360 different products that contain gelatin. Most of these are gelatin capsules for oral administration; however, I am aware of only a single case in which a gelatin capsule has been suspected of causing an allergic reaction.18 As would be expected, administering gelatin to a sensitized person by injection or intravenously, as with the reports above, would pose the greatest risk for anaphylaxis. Of interest is that all of the subsequent vaccine reports have come from Japan, and the subject of our original report is half Japanese. It is conceivable that ethnicity has some role in susceptibility to gelatin allergy, perhaps related to HLA types. A collaborative group of allergists and personnel from the Centers for Disease Control and Prevention and the Food and Drug Administration are currently evaluating patients in the US who have had anaphylactic reactions to MMR to determine whether large numbers are also allergic to gelatin. What can be done about the threat that allergy to gelatin poses? Gelatin is prepared by the hydrolysis of collagen from various animal sources (eg, bovine and porcine hide and bones). It is thus partially denatured protein. The more thorough the hydrolysis, the lower the molecular weight and the lower the gel melting point.11 In our original report of anaphylaxis to MMR vaccine caused by gelatin allergy,2 our patient had positive skin test responses to several flavored gelatins (Jell-O), as well as one unflavored gelatin (Knox). In inhibition immunoassays, all of these products, as well as the MMR vaccine itself, were good inhibitors of the patient’s antigelatin IgE. However, a second lot of the same brand of unflavored gelatin was a much less potent inhibitor. Furthermore, in immunoblot analysis the patient’s IgE antibodies recognized gelatin components of a variety of molecular weight in all of the gelatins, including the first lot of unflavored gelatin, but showed no bands to the second lot. Presumably, the source or processing of the second lot had rendered it less allergenic. This has been investigated further in a recent study in which gelatin was digested with collagenase to yield fractions of various molecular weights.19 The fraction with a molecular weight range from 2000 to 10,000 d showed considerably reduced reactivity with anti-gelatin IgE, yet maintained its adsorption blocking activity. Thus the gelatin used in vaccines may well be able to be altered in such a way as to maintain necessary pharmaceutical properties, yet not be allergenic.
202 Editorial
J ALLERGY CLIN IMMUNOL FEBRUARY 1999
The gelatin story continues to evolve. New insights gained into gelatin allergy should allow us to prevent these rare, but life-threatening, vaccine and medication reactions. John M. Kelso, MD Naval Medical Center San Diego, CA 92134-5000
REFERENCES 1. Physicians’ desk reference. 45th ed. Montvale (NJ): Medical Economics Company; 1991. 2. Kelso JM, Jones RT, Yunginger JW. Anaphylaxis to measles, mumps and rubella vaccine mediated by IgE to gelatin. J Allergy Clin Immunol 1993;91:867-72. 3. Herman JJ, Radin R, Schneiderman R. Allergic reactions to measles (Ruboela) vaccine in patients hypersensitive to egg protein. J Pediatr 1983;102:196-9. 4. Sakaguchi M, Nakayama T, Inouye S. Food allergy to gelatin in children with systemic immediate-type reactions, including anaphylaxis, to vaccines. J Allergy Clin Immunol 1996;98:1058-61. 5. Sakaguchi M, Yamanaka T, Ikeda K, Sano Y, Fujita H, Miura T, et al. IgEmediated systemic reactions to gelatin included in the varicella vaccine. J Allergy Clin Immunol 1997;99:263-4. 6. Kumagai, T, Yamanaka T, Wataya Y, Umetsu A, Kawamura N, Ikeda K, et al. Gelatin-specific humoral and cellular immune responses in children with immediate- and nonimmediate-type reactions to live measles, mumps, rubella, and varicella vaccines. J Allergy Clin Immunol 1997;100:130-4.
7. Ohsaki M, Tsutsumi H, Kumagai T, Yamanaka T, Wataya Y, Furukawa H, et al. The relevance of TH1 and TH2 cell in immediate and nonimmediate reactions to gelatin containing vaccine. J Allergy Clin Immunol 1999;103:276-81. 8. Borish L, Rosenwasser L. TH1/TH2 lymphocytes: doubt some more. J Allergy Clin Immunol 1997;99:161-4. 9. Nakayama T, Aizawa C, Kuno-Sakai H. Clinical analysis of gelatin allergy and causal relationship of past history of gelatin-containing acellular pertussis vaccine combined with diphtheria and tetanus toxoid. J Allergy Clin Immunol 1999;103:321-5. 10. Sakaguchi M, Kaneda H, Inouye S. A case of anaphylaxis to gelatin included in erythropoietin products. J Allergy Clin Immunol 1999;103:349-50. 11. Saddler JM, Horsey PJ. The new generation gelatin. Anaesthesia 1987;42:998-1004. 12. Lund N. Anaphylactic reaction induced by infusion of haemaccel. Br J Anaesth 1973;45:929. 13. Lundsgaard-Hansen P, Tschirren B. Clinical experience with 120,000 units of modified fluid gelatin. Dev Biol Stand 1980;48:251-6. 14. Freeman MK. Fatal reaction to haemaccel. Anesthesia 1979;34:341-3. 15. Wisborg K. Anaphylactic reaction induced by infusion of polygeline (haemaccel). Br J Anaesth 1973;47:1116-7. 16. Vervolet D, Fenft M, Dugue P, Arnaud A, Charpin J. Anaphylactic reactions to modified fluid gelatin. J Allergy Clin Immunol 1983;71:535-40. 17. Physicians’ desk reference. Version 3.02a—1998 release 2. Montvale (NJ): Medical Economics Company; 1998. 18. Haeney MR. Angio-edema and urticaria associated with omeprazole. Br Med J 1992;305:870. 19. Sakai Y, Yamato R, Onuma M, Kikuta t, Watanabe M, Nakayama T. Nonantigenic and low allergic gelatin produced by specific digestion with an enzyme-coupled matrix. Biol Pharm Bull 1998;21:330-4.
In July of 1991, I saw a 17-year-old woman in consultation because of an adverse reaction to measles, mumps, and rubella (MMR) vaccine. Within 5 minutes of receiving the vaccination, profuse rhinorrhea, total body itching and hives, lightheadedness, and a sensation of throat swelling had developed. She returned immediately to the clinic that had given her the immunization, where her blood pressure was recorded as 70/50, and she was treated appropriately with an injection of epinephrine. After treatment with diphenhydramine and a second dose of epinephrine, her symptoms eventually resolved. When later describing this vaccine reaction, she volunteered that the throat swelling was “kind of like what happens when I eat Jell-O.” She stated that whenever she ate gelatin, within a few minutes she would develop itching and swelling of her throat. Although I had never heard of allergy to gelatin, her history seemed quite convincing. Furthermore, a quick check of the Physicians’ Desk Reference1 revealed that MMR vaccine contains “hydrolyzed gelatin” as a “stabilizer.” Thus it seemed conceivable that her anaphylactic reaction to the vaccine was due to allergy to gelatin. Subsequent skin testing, immunoassays for IgE antibodies, inhibition immunoassays, and protein immunoblotting confirmed that the only component of the vaccine to which the patient made IgE antibody was indeed the gelatin.2 Allergic reactions to MMR vaccine had been thought most likely related to egg allergy.3 However, a review of the literature to date in 1993 (when this case was published) revealed that only 2 of 28 previous reports of anaphylactic reactions to measles or MMR vaccines were in subjects allergic to eggs, whereas literally hundreds of children allergic to eggs had received the vaccines uneventfully.2 This cast serious doubt on any relationship between egg allergy and adverse reactions to these vaccines. On the basis of this single case report,2 astute investi-
From the Department of Internal Medicine (Allergy Division), Naval Medical Center, San Diego. The views expressed in this article are those of the author and do not reflect the official policy or position of the Department of the Navy, Department of Defense, or the US Government. Received for publication Nov 2, 1998; accepted for publication Nov 4, 1998 Reprint requests: CDR John M. Kelso, MC, USN, c/o Clinical Research Department, Naval Medical Center, San Diego, CA 92134-5000. J Allergy Clin Immunol 1999;103:200-2. 1/1/95632
200
Abbreviations used DTaP: Diphtheria, tetanus, and acellular pertussis MMR: Measles, mumps, and rubella
gators in Japan set out to determine whether anaphylactic reactions to measles and mumps vaccines reported in 26 children there might also be due to gelatin.4 Twentysix age- and sex-matched children who had received the vaccines without allergic reactions served as control subjects. The researchers determined that 24 of the 26 children with immediate-type systemic allergic reactions to the vaccines (urticaria, wheezing, and hypotension) had IgE antibody to gelatin, whereas none of the control subjects produced such antibody. Furthermore, they discovered that 7 of the children had a history of hives after eating gelatin, and that in 5 of these 7, the clinical allergy to eating gelatin did not develop until after the vaccine reaction. Similarly, with varicella vaccine, 3 of 4 children with anaphylactic reactions to the vaccine were found to have anti-gelatin IgE, whereas none of 50 control subjects had such antibodies.5 These studies suggested that immediate-type allergic reactions to gelatin-containing vaccines are most often due to allergy to gelatin. A subsequent report examined cellular immune responses in children with both immediate and delayed adverse reactions to MMR and varicella vaccines.6 As with the earlier studies, 6 of 6 patients with histories of immediate-type allergic reactions had anti-gelatin IgE. Also studied were 21 patients with histories of delayed adverse reactions to the vaccines, either redness and swelling at the injection site or a nonurticarial rash that developed several to 48 hours after the immunizations. None of the 21 had anti-gelatin IgE. Specific cellular immune responsiveness to gelatin was studied by in vitro lymphocyte proliferation assay and antigen-specific IL-2 responsiveness. The results of one or both of these assays was positive in all 6 of the patients with immediate reactions and in 17 of the 21 patients with delayed reactions. The tests were negative in 14 control subjects, who had no adverse reaction to the vaccines. This report suggested that lymphocyte responses were involved in both immediate- and delayed-type reactions to gelatincontaining vaccines. Three articles appear in this issue of The Journal that add to the gelatin story. First, Ohsaki et al7 further define T-cell responses in subjects’ reactions to gelatin-containing
J ALLERGY CLIN IMMUNOL VOLUME 103, NUMBER 2, PART 1
vaccines. As might be expected, among 8 subjects with a history of immediate-type allergic reactions to the vaccines and positive test responses for anti-gelatin IgE, incubation of PBMCs with gelatin induced production of mRNA for IL-4, IL-13, or both, which is consistent with a TH2-type response. By contrast, among 8 subjects with delayed reactions to the vaccines, none had any induction of IL-4 mRNA, and 4 had low-level induction of IL-13 mRNA. The picture with the so-called TH1 cytokines, IFN-γ and IL-2, was less clear. All subjects with immediate-type reactions also had robust induction of mRNA for one or both of these cytokines, whereas only 3 of the 8 subjects with delayed reactions had such responses. These 3 were among the 4 who also had induction of IL-13 mRNA. This heterogeneity of responses in subjects with delayed reactions may well reflect that this is a heterogeneous group of patients. Some reactions, such as local redness and swelling, may not be immune mediated at all. No mRNA for these cytokines could be induced in 6 control subjects without any history of adverse reaction to the vaccines. This study further supports and defines the role of TH2 cytokine–driven, IgE-mediated responses to gelatin as important in immediate allergic reactions to gelatin-containing vaccines. As to the TH1 responses, the title of a recent editorial in The Journal says it best, “TH1/TH2 lymphocytes: doubt some more.”8 One question raised by gelatin-related allergic reactions to vaccines is as follows: How did the subjects become sensitized to gelatin in the first place? As above, clinical allergy to the ingestion of gelatin may or may not be present in patients who have allergic reactions to the systemic injection of gelatin.4 Reactions to a gelatin-containing vaccine may occur after the first dose of vaccine because of prior exposure to (and sensitization from) gelatin in other medications or vaccines or by ingestion of gelatin-containing foods. The second article, by Nakayama et al,9 addresses this question. From 1989 to 1993 in Japan, a trivalent MMR vaccine was administered, followed by a series of diphtheria, tetanus, and acellular pertussis (DTaP) vaccines. During this time, no anaphylactic reactions to MMR vaccines were reported. Since 1994, the DTaP series has been given before monovalent MMR vaccines. Since this change in vaccine schedule, numerous reports of anaphylactic reactions to the MMR vaccines have been received. Both the trivalent and the monovalent MMR vaccines contain the same 0.2% gelatin added as a stabilizer; however, only some brands of DTaP vaccine contain gelatin. Among the subjects reported with adverse reactions, almost all had received gelatin-containing DTaP. Thus prior injection with gelatin-containing DTaP vaccine may be the cause of sensitization to gelatin and the subsequent reaction to other gelatin-containing vaccines. In the third article, Sakaguchi et al10 describe how another route of gelatin-containing medication administration can cause anaphylaxis. A patient had anaphylaxis when administered intravenous epoetin (recombinant erythropoietin) that contained gelatin but tolerated anoth-
Editorial 201
er epoetin product without gelatin. She had anti-gelatin IgE but not antiepoetin IgE, implicating gelatin allergy as the cause of her allergic reactions. A number of intravenous gelatin solutions are used as plasma expanders in Europe.11 Anaphylactic reactions have been reported in association with the infusion of these products,12,13 including 2 fatalities.13,14 Some patients who have had such reactions have had positive skin test responses to the gelatin solutions.12,15,16 Thus intravenous gelatin may also induce allergic reactions to gelatin. An electronic search of the 1998 Physicians’ Desk Reference,17 revealed 360 different products that contain gelatin. Most of these are gelatin capsules for oral administration; however, I am aware of only a single case in which a gelatin capsule has been suspected of causing an allergic reaction.18 As would be expected, administering gelatin to a sensitized person by injection or intravenously, as with the reports above, would pose the greatest risk for anaphylaxis. Of interest is that all of the subsequent vaccine reports have come from Japan, and the subject of our original report is half Japanese. It is conceivable that ethnicity has some role in susceptibility to gelatin allergy, perhaps related to HLA types. A collaborative group of allergists and personnel from the Centers for Disease Control and Prevention and the Food and Drug Administration are currently evaluating patients in the US who have had anaphylactic reactions to MMR to determine whether large numbers are also allergic to gelatin. What can be done about the threat that allergy to gelatin poses? Gelatin is prepared by the hydrolysis of collagen from various animal sources (eg, bovine and porcine hide and bones). It is thus partially denatured protein. The more thorough the hydrolysis, the lower the molecular weight and the lower the gel melting point.11 In our original report of anaphylaxis to MMR vaccine caused by gelatin allergy,2 our patient had positive skin test responses to several flavored gelatins (Jell-O), as well as one unflavored gelatin (Knox). In inhibition immunoassays, all of these products, as well as the MMR vaccine itself, were good inhibitors of the patient’s antigelatin IgE. However, a second lot of the same brand of unflavored gelatin was a much less potent inhibitor. Furthermore, in immunoblot analysis the patient’s IgE antibodies recognized gelatin components of a variety of molecular weight in all of the gelatins, including the first lot of unflavored gelatin, but showed no bands to the second lot. Presumably, the source or processing of the second lot had rendered it less allergenic. This has been investigated further in a recent study in which gelatin was digested with collagenase to yield fractions of various molecular weights.19 The fraction with a molecular weight range from 2000 to 10,000 d showed considerably reduced reactivity with anti-gelatin IgE, yet maintained its adsorption blocking activity. Thus the gelatin used in vaccines may well be able to be altered in such a way as to maintain necessary pharmaceutical properties, yet not be allergenic.
202 Editorial
J ALLERGY CLIN IMMUNOL FEBRUARY 1999
The gelatin story continues to evolve. New insights gained into gelatin allergy should allow us to prevent these rare, but life-threatening, vaccine and medication reactions. John M. Kelso, MD Naval Medical Center San Diego, CA 92134-5000
REFERENCES 1. Physicians’ desk reference. 45th ed. Montvale (NJ): Medical Economics Company; 1991. 2. Kelso JM, Jones RT, Yunginger JW. Anaphylaxis to measles, mumps and rubella vaccine mediated by IgE to gelatin. J Allergy Clin Immunol 1993;91:867-72. 3. Herman JJ, Radin R, Schneiderman R. Allergic reactions to measles (Ruboela) vaccine in patients hypersensitive to egg protein. J Pediatr 1983;102:196-9. 4. Sakaguchi M, Nakayama T, Inouye S. Food allergy to gelatin in children with systemic immediate-type reactions, including anaphylaxis, to vaccines. J Allergy Clin Immunol 1996;98:1058-61. 5. Sakaguchi M, Yamanaka T, Ikeda K, Sano Y, Fujita H, Miura T, et al. IgEmediated systemic reactions to gelatin included in the varicella vaccine. J Allergy Clin Immunol 1997;99:263-4. 6. Kumagai, T, Yamanaka T, Wataya Y, Umetsu A, Kawamura N, Ikeda K, et al. Gelatin-specific humoral and cellular immune responses in children with immediate- and nonimmediate-type reactions to live measles, mumps, rubella, and varicella vaccines. J Allergy Clin Immunol 1997;100:130-4.
7. Ohsaki M, Tsutsumi H, Kumagai T, Yamanaka T, Wataya Y, Furukawa H, et al. The relevance of TH1 and TH2 cell in immediate and nonimmediate reactions to gelatin containing vaccine. J Allergy Clin Immunol 1999;103:276-81. 8. Borish L, Rosenwasser L. TH1/TH2 lymphocytes: doubt some more. J Allergy Clin Immunol 1997;99:161-4. 9. Nakayama T, Aizawa C, Kuno-Sakai H. Clinical analysis of gelatin allergy and causal relationship of past history of gelatin-containing acellular pertussis vaccine combined with diphtheria and tetanus toxoid. J Allergy Clin Immunol 1999;103:321-5. 10. Sakaguchi M, Kaneda H, Inouye S. A case of anaphylaxis to gelatin included in erythropoietin products. J Allergy Clin Immunol 1999;103:349-50. 11. Saddler JM, Horsey PJ. The new generation gelatin. Anaesthesia 1987;42:998-1004. 12. Lund N. Anaphylactic reaction induced by infusion of haemaccel. Br J Anaesth 1973;45:929. 13. Lundsgaard-Hansen P, Tschirren B. Clinical experience with 120,000 units of modified fluid gelatin. Dev Biol Stand 1980;48:251-6. 14. Freeman MK. Fatal reaction to haemaccel. Anesthesia 1979;34:341-3. 15. Wisborg K. Anaphylactic reaction induced by infusion of polygeline (haemaccel). Br J Anaesth 1973;47:1116-7. 16. Vervolet D, Fenft M, Dugue P, Arnaud A, Charpin J. Anaphylactic reactions to modified fluid gelatin. J Allergy Clin Immunol 1983;71:535-40. 17. Physicians’ desk reference. Version 3.02a—1998 release 2. Montvale (NJ): Medical Economics Company; 1998. 18. Haeney MR. Angio-edema and urticaria associated with omeprazole. Br Med J 1992;305:870. 19. Sakai Y, Yamato R, Onuma M, Kikuta t, Watanabe M, Nakayama T. Nonantigenic and low allergic gelatin produced by specific digestion with an enzyme-coupled matrix. Biol Pharm Bull 1998;21:330-4.