Minimizing allergen concentration in latex goods to prevent NRL sensitization and thereby the development of clinical allergy is acknowledged as being of mutual interest for rubber manufacturers and regulatory health authorities. The modified Lowry method is currently the method of choice for manufacturers to determine the total protein concentration and hereby roughly estimate the amount of allergens in glove extracts. Although the Lowry results seem to correlate relatively well with the true NRL-allergen content measured by skin prick testing (SPT) (r = up to 0.80) or latex-specific human IgEbased methods,1,2 the information obtained is neither specific nor accurate enough to set any safety limits.
About 250 proteins or polypeptides have been identified in the liquid NRL by 2-dimensional electrophoresis. Of them, 50-60 show allergenic properties.3 According to the published literature, only a few
of the characterized 11 NRL allergens (Hev b1-Hev b11) have unequivocally been demonstrated to find their way into manufactured rubber products. Of these, 2 hydrophilic proteins, Hev b6.02 (hevein, MW 4719 Da), and Hev b5 (acidic, MW 16 kDa) are major allergens for adults. Two hydrophobic rubber particle proteins (Hev b1, MW 14.6 kDa and Hev b3, MW 22 kDa) are, in turn, major allergens for children with spina bifida and/or other congenital malformations, requiring multiple surgical operations at an early age.
Allergen content of glove extracts have been successfully measured by SPT in voluntary latex-allergic patients4 but due to ethical constraints this approach cannot be routinely used. Therefore, human IgE-based in vitro immunoassays have been developed to measure total latex allergen levels. IgE-immunoblotting after sodium-dodecylsulphate polyacrylamide-gel-electrophoresisis (SDS-PAGE) has turned out to be unsatisfactory, due to insufficient sensitivity and the fact that small molecular weight peptides (such as Hev b6.02) usually escape detection. Latex RAST-inhibition5 and IgE-ELISA inhibition2 seem to reliably measure allergenicity. The ELISA-inhibition2 correlated well with both skin prick testing (r = 0.94) in latex-allergic volunteers and also with RAST-inhibition (r = 0.96). The assay is very reproducible, but all human IgE-based methods carry major problems in the limited availability of suitable antisera and in difficulties in standardizing the assays. In addition, it will be increasingly difficult to ensure that sufficient levels of IgE antibodies to Hev b1 and Hev b3 can be maintained in the serum pools.
Recently, a novel capture ELISA has been developed, based on the use of a selection of clinically relevant purified or recombinant allergens known to exist in NRL gloves, along with their corresponding monoclonal antibodies. The assay is the result of a collaborative research and development project by a Finnish biotechnology company (FIT Biotech Ltd., Tampere, Finland) and a Finnish latex allergy research group. NRL allergens most often found in gloves were shown to be Hev b6.02 and Hev b5.6 Assays for Hev b 1, 3, 5, and 6.02 are now commercially available. The pressing need for reliable NRL allergen-measuring methods is today generally admitted and regulatory health authorities as well as rubber manufacturers worldwide have expressed interest towards such methods.
REFERENCES
- Yip E, Turjanmaa K, Ng PH, Mok KL. Allergic responses and levels of extractable proteins in NR gloves and dy rubber products. J Nat Rubber Res 1994; 9:79-86.
- Palosuo T, Mäkinen-Kiljunen S, Alenius H, Reunala T, Yip E, Turjanmaa K. Measurement of natural rubber latex allergen levels in medical gloves by an allergen-specific IgE-ELISA-inhibition, RAST-inhibition and skin prick testing. Allergy 1998; 53:59-67.
- Alenius H, Kurup V, Kelly K, Palosuo T, Turjanmaa K, Fink J. Latex allergy: Frequent occurrence of IgE antibodies to a cluster of 11 latex proteins in patients with spina bifida and histories of anaphylaxis. J Lab Clin Med 1994; 123:712-720.
- Turjanmaa K, Laurila K, Mäkinen-Kiljunen S, Reunala T (1988) Rubber contact urticaria. Allergenic properties of 19 brands of latex gloves. Contact Dermatitis 19:362-367.
- Yunginger J, Jones R, Fransway A, Kelso J, Warner M, Hunt L, Reed C Extractable latex allergens and proteins in disposable medical gloves and other rubber products. J Allergy Clin Immunol 1994; 93:836.
- Palosuo T, Ovod V, Kärkkäinen T, Kalkkinen N, Kulomaa M, Reunala T, Turjanmaa K, Reinikka-Railo H. The major latex allergens Hev b6.02 (hevein) and Hev b 5 are regularly detected in medical gloves with moderate or high allergen content. J Allergy Clin Immunol 2001; 107:S321.
