rHev b 8 Profilin, Latex

Code: k221
Latin name: Hevea brasiliensis
Common names: Profilin
Recombinant allergen
Hevea brasiliensis allergen Hev b 8
 
Biological function
Actin-binding protein.
 
Mw
14 kDa
 
Allergen description
Hev b 8 (1-2, 4-5) is a profilin. Plant profilins are important panallergens. They are responsible for a significant percentage of pollen-related allergies. The observed frequencies of Hev b 8-specific IgE antibodies in sera of Latex-allergic patients in different risk groups range between 6 and 24% (3-6).

rHev b 8 has a sequence identity of 75% with Birch profilin (Bet v 2) (3). Recombinant isoforms of Hev b 8 with marginal differences in the amino acid sequence were reported to have no influence on the IgE-binding properties of the rHev b 8 isoforms. In a study evaluating the prevalence of serum IgE antibodies to rHev b 8, among 17 SB patients, IgE antibodies to rHev b 8 were found in 2, and in 5 of 25 sera (20%) from HCW. Further studies demonstrated the presence of IgE-binding epitopes on the Hev b 8 molecule which did not cross-react with Birch profilin. The study concluded that Latex profilin represents a minor allergen in Natural rubber latex (NRL) and may have IgE-binding epitopes different from Bet v 2 (4).

These factors may explain the variability in the prevalence of allergen-specific IgE binding to Latex profilin in studies. For example, skin tests and allergen-specific IgE antibodies to natural and recombinant purified Hev b 8 were positive in 15 of 17 spina bifida (SB) children and all 14 adults allergic to Latex. However, only 42% of the Latex-allergic patients had allergen-specific IgE levels of 0.35 kUA/L or higher, and only 39% of them exhibited IgE binding with any natural or recombinant Hev b 8 forms (2).

Between 30% and 50% of individuals who are allergic to Latex products are also allergic to specific plant foods, and this is aptly described as Latex-fruit syndrome. However, the roles of the Latex chitinase, Latex profilin and Latex beta-1,3-glucanase need to be clarified. This is well illustrated in a study, which reviewed simultaneous sensitisation to Latex and Bell pepper, sensitisation that had previously been reported. In sera of 4 patients with allergy to Latex and Bell pepper, 3 were shown to have IgE antibodies to profilin from Bell pepper and Latex. Two patients also had IgE antibodies to Hev b 2 (a beta-1,3-glucanase) and a homologous protein in Bell pepper. One patient was shown to have allergenspecific IgE to an L-ascorbate peroxidase, and another patient to a 38 kDa protein. The study concluded that Hev b 2 (beta-1,3- glucanase) and the Bell pepper L-ascorbate peroxidase were also cross-reactive allergens, and that profilin was responsible for some of the IgE cross-reactivity (7). 

Similarly, other studies have demonstrated the variable responsibility of profilin in cross-reactivity between Latex profilin and other plant profilins. In a study of sera of 36 individuals containing IgE antibodies to Ragweed profilin, 35 reacted with profilin from Latex, indicating structural homologies between profilins from Latex and Ragweed. Fifty-nine percent of these sera were found to be positive for Latex-specific IgE. As profilin is also present in Banana, it was proposed that Latex profilin would likely be involved in crossreactivity between Banana and Latex. However, among 19 individuals allergic to Latex, only 2 had anti-profilin IgE antibodies. The authors suggested that IgE antibodies to Latex profilin might be a questionable factor in sensitisation of occupationally exposed patients, but that sensitisation to profilin should be taken into account when interpreting the results of Latex-specific IgE investigation (5).

Recombinant profilin from Banana and Pineapple has a high sequence identity (71- 84%) to known allergenic pollen and food profilin. In a study demonstrating IgE binding in sera to recombinant profilin, in 7/16 (44%) subjects with suspected Banana allergy, and in 8/19 (42%) subjects with suspected Pineapple allergy, high cross-reactivity to Birch pollen profilin Bet v 2 and Latex profilin Hev b 8 was demonstrated. Profilin was therefore shown to be an important mediator of IgE cross-reactivity between pollen and exotic fruits (8-9).

In a study using rHev b 8 to screen sera from Latex-allergic HCW with well documented histories of food and pollen allergy and Latex-allergic SB patients, 12 of the 50 HCW and 2 of the 34 SB patients were sensitised to Hev b 8. All Hev b 8- sensitised patients showed allergic symptoms to pollen or plant foods. Cross-reactivity among profilins of Latex, pollen and plant food was demonstrated by their ability to inhibit IgE binding to rHev b 8. The authors concluded that primary sensitisation to Latex profilin in the majority of cases took place via pollen or food profilin, and that pollen- and food-allergic patients with profilin-specific IgE antibodies could be at risk of developing Latex allergy (3).

Other studies have also demonstrated the relevance of Latex profilin cross-reactivity, for example between Chenopodium profilin and Latex (10), and between 2 Rice profilin cDNAs (highly homologous to each other) and profilin from Maize, Bermuda grass, Timothy grass and Latex (11). 

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.