Behcet's Disease Associated with HLA-B51 and DRw52 Antigens in Italians
Olavio R. Baricordi, Alberto Sensi, Paola Pivetti-Pezzi, Salvatore Perrone, Alessandra Balboni, Giovanni Catarinelli, Fabrizio Filippi, Loredana Melchiorri, Alfio Moncada, and Pier Luigi Mattiuz
Abstract
Thirty-eight Italian patients with Behcet's disease, all with ocular involvement, (28 complete type and ten incomplete) were typed for HLA A,B,DR, and DQ antigens. A significant increase of HLA-B51 (p < 0.00001) and DRw52 (p = 0.045) with no significant difference between complete and incomplete syndrome was found. The involvement of B51 antigen as the main immunogenetic factor in the disease is suggested by the high value of relative risk (RR = 16.03). However, the association with the II class antigen DRw52 (RR = 2.77) cannot be easily explained as a secondary association due to linkage disequilibria with B51.
Abbreviations
BD Behcet's disease RR relative risk
Introduction
Behcet's disease (BD) is a multifocal syndrome due to an inflammatory vasculitis and characterized by affections at eyes, mouth, genitals, skin, joints, and brain. Although the etiology is still unknown, several reports suggest immunological abnormalities as pathogenetic elements [1-4]. Furthermore, the involvement of immunogenetic factors is strongly suggested by the association between the HLA B5 antigen and the disease, first reported by Ohno et al. in Japanese patients [5], and subsequently confirmed in different ethnic groups [6-9]. When the B5 specificity was subdivided into B51 and Bw52, B51 resulted strongly associated with the ocular type of the disease [10]. However, other HLA specificities showed significant associations with the disease: B12 with the mucocutaneous type [11] and B27 with the arthritic type [12]. Recently, the association between HLA-D region antigens and BD has been investigated in Japanese patients, showing an increase of DRw52 (MT2) [13-15] and a decrease of DQw1 [15]. A similar study in Caucasoid patients, suffering for ocular lesions, reported an increase of HLA-B5 and DR7 antigens [11,16]. In the present study, we have investigated the associations of HLA class I and II antigens with BD in Italians. Furthermore, we have tested the reactivity of the monoclonal antibody 9w 925-HU39 detecting a structure associated with the disease on B lymphocytes of Japanese patients [15].
Materials and Methods
Population. The study is based upon 38 (27 males and 11 females) Italian Behcet patients, aged 18 to 61, all with ocular lesions and diagnosed as complete (n = 28) and incomplete (n = 10) type according to the clinical criteria proposed by the Behcet's Disease Research Committee of the Japanese Ministry of Health and Welfare [17].
Control frequencies for HLA-A, B (n = 522) and private DR (n = 455) specificities were obtained from healthy unrelated Caucasoids individuals typed in Italy during the VIII Histocompatibility Workshop [18]. Italian unrelated subjects, typed during the IX Histocompatibility Workshop (n = 68) [15], served as controls for DRw52, DRw53, and DQ frequencies.
Typing. HLA typing was performed by conventional two-step complement de pendent microlymphocytotoxicity on peripheral blood lymphocytes or enriched B lymphocytes preparations by nylon wool column [19]. Ninth International Histocompatibility Workshop and correlated local sera were used to define the HLA-A (n = 13) - B (n = 23) - DR (n = 12), and DQ (n = 3) specificities. MoAb 9W925-HU39 was kindly provided by Dr. M. Aizawa (Sapporo).
Statistics. Statistical significance of associations were evaluated by Fisher's exact p test. Correction of p values for multiple comparisons (pc) was performed for associations not previously reported by multiplying the number of antigens tested by the calculated p value. The relative risk (RR) was estimated from the 2 x 2 table data.
Results
B51 specificity was observed in 31 of the 38 patients examined, with no significant difference between the complete and incomplete type of the disease. The anti genic frequency observed showed a significant increase (81,5% vs. 21,7% in controls, p < 0.00001) with a RR of 16.03. No positive significant associations were observed between other HLA-A and -B determinants and the disease except for A24 (p = 0.019; pc = NS). Protective antigens were sought by comparing the observed frequencies with those expected on the basis of the compensatory decrease [20]. None were found.
The frequencies observed for the HLA-D region antigens are reported in Table 1. The results showed significant increases for DRw52 (p = 0.04 5; RR = 2. 77) and DQw3 (p = 0.013; pc = NS) specificities in the patients when com pared to controls.
Analysis of the reactivity of monoclonal antibody 9w 925-HU39, associated in Japanese patients with the disease (61.1% vs. 25.0 in controls, p < 0.0003), showed no significant difference between controls and patients (30.8% vs. 27.1%) in Italians.
From a clinical standpoint it is worthwhile to note that no significant differences

in the antigens frequencies were observed between the complete and incomplete type of the disease.
Discussion
The analysis performed in a series of Italian BO patients confirms the strong association between HLA-BS 1 and the disease, as previously observed in different ethnic groups [9,10,13-15].
Our data on the HLA-DR antigens in BO confirm neither the increase of DR7 antigen observed in Caucasoid patients by Lehner et al. [11,16] nor the strong association between 9w925-HU39 target antigen and the disease in Japanese patients [15].
On the other hand, the significant increase of ORw52 in Italian patients is in agreement with the recent studies in the Japanese population [13-15]. Further more, DQwl was reported to be decreased in Japanese patients [15]. An altered DQ distribution was noted in Italian patients also, with an increased frequency of DQw3, which was not significant after correction for the number of antigens tested.
The observed increase of DRw52 specificity in BD might be merely due to its linkage disequilibrium with B51. Indeed, linkage disequilibrium between B51 and DRw11 (DRS), and between DRw11 and DRw52 has been reported in Caucasians [21]. However, it is worthwhile noting that in our study: (i) DRS is not significantly increased in patients; (ii) all seven B51 negative patients were DRw52 positive (p = 0.08 NS); (iii) when only DRS negative cells are taken into account, DRw52 retains its significant association (p < 0.05). Consequently, it is unlikely that the linkage disequilibrium between BS l and DRw52 is the explanation for the increased frequency of DRw52 in Italian Behcet patients.
The immunological functions mediated by MHC molecules suggest the direct biological involvement of HLA products in the etiopathogenesis of autoimmune and immunopathologically mediated diseases [22-25]. The two probably independent associations of BD with B51 and DRw52 could be regarded in the light of this functional hypothesis.
Acknowledgments
This work was supported by CNR "Progetto finalizzato ingegneria genetica e basi molecolari delle malattie ereditarie" 84.00877. 51 and by "Fondo Ministeriale per la Ricerca Scientifica (40%)." The excellent technical assistance of Mrs. Maria Teresa Grappa is gratefully acknowledged.
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