Throughout the world rhus dermatitis represents a well-known type of allergic contact dermatitis and rhus trees continue to be a common cause of this dermatitis.
Despite the rapid development of urbanization this is the case at present, because of greater likelihood of exposure to the plant through the ever-increasing popularity of informal out-door living and relaxation during summer, the usefulness of the trees in herb medicine, application of lacquer-painting of luxurious
furnitures and so on. There exist 5 rhus trees belonging to the family Anacardacease in this country; Rhus verniciflus, Stokes., Rhus trichocarpa, Miquel., Rhus javanica, Linne., Rhus sylvestris, Siebold., and Rhus succedanea, Linne(Chung, 1965).
The exact incidence of rhus sensitivity is still unknown. However, it was estimated that at least the half of adult population is allergic to poison ivy (Rhus radicans) and poison oak (Rhus toxicodendron) (Kligman, 1958; Fisher, 1967),
and Woo et al. (1972) found that about 30% of patients of allergic contact dermatitis were reactive to lacquer Rhus verniciflua in routine patch test.
Kook and Woe (1971) demonstrated that incidences of latent hypersensitivity to dried leaves of Rhus verniciflua, Rhus trichocarpa, Rhus javanica, Rhus sylvestris and lacquer of Rhus verniciflua were 37.5%, 27.5%, 21.0%, 28.3% and 29.7%
respectively, and that the leaf of each rhus contained specific antigenic substance which was different from lacquer of Rhus verniciflua.
It has been established that rhus dermatitis is caused by an oleoresin known as urushiol, of which the active component is 3-n-pentadecylcatechol and this catechol can produce cross-reactions with other plants belonging to the family Anacardaceae
(Dawson, 1954; Baer et al., 1963; Fisher, 1967; Domonkos, 1971: Gellin et al., 1971). On the other hand, Mason and Lada (1963) pointed out that poison ivy urushiol is a minor antigenic component of poison ivy, and Baer (1963) reported the immunologic unresponsiveness of adult guinea pigs to a component of poison ivy extract (3-n-pentadecylcatechol). Based on Mason and Bowser's suggestion, it could be postulated that there is a specific substance in each rhus, different from urushiol, and we have shown previously that the antigenic substance is specific and
differed from urushiol (Kook and Woo, 1971).
Studies were made in this investigation on the extraction from Korean rhuses of antigenic substances which are different from urushiol, identification of active components of the substances and establishment of the specificites of extracted antigenic substances by patch test in human volunteer experiment.
Materials arid Methods Dried leaves of Rhus verniciflua, Rhus trichocarpa and Rhus javanica were included in the extraction experiment. The methods of extraction of antigenic substances consisted of extraction with either acetone or ethyl alcohol while homogenization in Waring blendor or tissue grinder, separation of the supernatant and the residue by filtration and centrifugation of the extracts, and further extraction of the residue with hexane into the supernatant and the residue. The
extracted substances and original dried leaves, lacquer of Rhus verniciflua, urushiol and turpentine were all included for the closed patch test (Fisher, 1967) in human volunteers who were sensitive to rhus leaf.
The hexane-supernatant was further fractionated by thin-layer chromatography of Randerath (1965) and each fraction was also included in the patch test.
Results and Discussion
1. Patch tests with the extracts and common antigenic substances of rhus trees. By results of the patch tests the volunteers could be subdivided into 2 groups. In the first group which included 47 individuals, visible reactions was observed in the patch tests with rhus leaf, its acetone and alcoholic extracts, lacquer, turpentine and urushiol simultaneously but they proved to be non-reactive to its hexane extracts. The results established that common antigenic substances of rhus leaves could be completely extracted by acetone or ethyl alcohol solvents.
In the 2nd group of 13 volunteers, there observed visible reactions only in the patch tests with rhus leaf itself and its hexane extraction products but they were all non-reactive to the common antigenic substance and other extracts included in this study. These data indicated that certain specific antigenic substances, differed completely from the common antigenic substances, could be extracted from rhus leaves with hexane solvent.
The volunteers of the 2nd group were further tested with fractionated components of the hexane-supernatant.
2. Fractionation by thin-layer chromatography of the extracts and common antigenic substances of rhus.
Lacquer, turpentine and urushiol exhibited almost the same fractionation pattern and the fractionation study showed that the urushiol is a major component of lacquer of the rhus tree. Fractionation patterns of both acetone and ethyl alcohol extract were almost same as lacquer, and there observed no difference in the fractionation patterns of Rhus verniciflua, Rhus trichocarpa and Rhus javanica.
Active components of acetone and ethyl alcohol extracts of rhus were shown to be identical in both fractionation pattern by thin-layer chromatography and patch teat results. Finally, it was demonstrated that the common antigenic substances of rhus were extracted with acetone or ethyl alcohol solvent.
3. The fractionation of hexane extracts of rhus leaves.
The fractionation patterns of hexane extracts of 3 rhus leaves were different from one another and also from those of lacquer. These results demonstrated that the specific antigenic substance is soluble in hexane and is different from acetone or ethyl alcohol soluble ones.
4. Identification of the specific fraction of hexane extracts of 3 rhus trees.
Each of fractions obtained from hexane extracts of 3 rhuses by thin-layer chromatography was recollected from the plates in powdery form, eluted with hexane and used for patch tests for the final identification of respective specific antigenic fractions.
The hexane-soluble antigenic substances obtained from the leaves of each rhus were different from one another and from the common antigenic substances, and they appeared to be chemically and immunologically specific.
Fractionation experiments demonstrated that a specific antigenic substance of Rhus vern-iciflua is a faintly yellowish fluorescence substance with R^^F value of 0.45, of Rhus trichocarpa a yellowish under visible light and yellow-greenish
fluorescening substance having R^^F value of 0.6, and of Rhus javanica a yellowish material under both visible and fluorescent light having R^^F value of 0.5.
This study established that each of 3 rhus trees which are distributed widely in Korea contains a hexane-soluble specific antigen that is different from the common antigens, urushiol, lacquer and turpentine.
It is suggested that the specific causative allergen responsible for rhus dermatitis differed from the formerly known extracts of rhus, and that further studies on the chemical composition and the methods of identification of the specific antigenic substance will be very much useful for the prevention and treatment of rhus dermatitis, seasonal rhinitis and even asthma due to pollen of rhus trees.