Key words: latex, allergy, protein measurement, tech support, research
Natural latex in medical devices frequently induces a Type 1 allergy which may be life threatening in individuals highly sensitized to latex proteins. Although awareness of allergy to latex proteins has increased in the last five years, the prevalence of latex sensitization is increasing in the general population. One of the most prominently affected groups, due to the frequent and extended exposure to latex gloves, is healthcare professionals. The prevalence of latex allergy in this group is estimated to be up to 15%. Due to the severity of reactions, sensitized individuals either avoid using latex gloves or are forced to change their occupation. The potential for reduced usage of protective latex products (gloves and condoms) by increasing number of sensitized individuals may have a detrimental effect on the further spreading of HIV and other infections.
General research efforts are focused on identifying allergenic proteins and reducing protein levels on finished latex products. Present laboratory and clinical studies include several in vitro and in vivo approaches for evaluation of allergenic potential of latex products and identification of latex sensitized individuals. However, the clinical relevance of various in vitro methods has not been established, and the identity of all latex allergens had not been determined yet.
The purpose of this project was to evaluate the specificity of the anti-latex IgE antibodies in human sera reacting with latex proteins from various sources. These findings have been correlated with the medical history of test subjects and specific exposure profiles. This study revealed : (a) the existence of a number of major allergenic proteins that are present in various latex products, and (b) that the specificity of allergenic response depends on the type of product and the pattern of exposure. While the profile of allergenic proteins varies from product to product, all proteins were present in non-ammoniated raw latex. Therefore, the studies were extended to evaluate the relationship between total protein content on latex products and potential allergenicity. Latex protein extracts from three major sources (non-ammoniated and ammoniated raw latex and latex products) were compared for total protein content. In addition, the level of allergenic proteins was determined using a pool of human sera and the intensity of skin reactions in sensitized individuals. In earlier clinical studies, skin testing was performed with these three extracts and dosing was normalized according to the total protein levels. The intensity of skin reactions was the same for all extracts. This finding indicated that the total protein level may be a reliable measure of the potential allergenicity of latex products. Correlation of the total protein measurement and RAST inhibition test, as an in vitro measure of allergenic potential, is in progress. To confirm this finding, OST scientists are further extending the study to make similar comparisons of two in vitro tests on the wide range of extracts from finished latex products. Protein extracts from surgical and examination gloves and other latex products (15 total) will be evaluated for total protein levels and allergenic protein levels. Selected samples from this group will be evaluated by skin testing also.
In efforts to develop a more sensitive method for reliable measurement of protein levels on the medical devices, OST investigators generated pilot data for enzymatic assay of latex proteins. Several attempts to develop an ELISA for latex proteins raised the question of an appropriate source of latex protein to represent standard reference antigen. OST scientists evaluated a series of sera from rabbits immunized with latex proteins extracted from ammoniated and non-ammoniated latex (NAL) and from latex gloves. Capacity and selectivity of protein recognition by those sera was evaluated by immunoblotting. The results demonstrated that the largest number of protein molecules in extracts from various sources was recognized by serum from NAL-immunized rabbits, suggesting that NAL represents the most complete source of latex proteins including all potential allergens. Therefore, NAL was selected as the standard source of latex proteins. A large quantity of NAL was obtained from the Rubber Research Institute of Malaysia. Standard proteins were used generate a standard pool of rabbit anti-latex sera. The serum pool and the standard protein were used to optimize the assay. The protocol is being validated in several other laboratories. Upon completion, the method will be submitted to the ASTM as potential standard test for evaluation of the potential allergenicity of latex-containing medical devices.