Little is known of the role of classical HLA-A and -B class I alleles in determining resistance, susceptibility, or the severity of acute viral infections. Appropriate paradigms for immunogenetic studies of acute viral infections are dengue fever (DF) and dengue hemorrhagic fever (DHF). Both primary and secondary infections with dengue virus (DEN) serotypes 1, 2, 3 or 4, can result in either clinically less severe DF or the more severe DHF. In secondary exposures, a memory response is induced in immunologically primed individuals, which can both clear the infecting dengue virus and contribute to its pathology. In a case-control study of 263 ethnic Thai patients infected with either DEN-1, -2, -3 or -4, we detected HLA class I associations with secondary infections, but not in immunologically naive patients with primary infections. HLA-A*0203 was associated with the less severe DF, regardless of the secondary infecting virus serotype. By contrast, HLA-A*0207 was associated with susceptibility to the more severe DHF in patients with secondary DEN-1 and DEN-2 infections only. Conversely, HLA-B*51 was associated with the development of DHF in patients with secondary infections, and HLA-B*52 was associated with DF in patients with secondary DEN-1 and DEN-2 infections. Moreover, HLA-B44, B62, B76 and B77 also appeared to be protective against developing clinical disease after secondary dengue virus infection. These results confirm that classical HLA class I alleles are associated with the clinical outcome of exposure to dengue virus, in previously exposed and immunologically primed individuals.

We recently reported association of a newly identified polymorphism of Fcgamma receptor (FcgammaR) IIb, I232T, with systemic lupus erythematosus (SLE) in Japanese. To date, information on FcgammaR genotypes and their association with SLE is limited in South-east Asian populations. To gain further insight into the role of FcgammaR polymorphisms in the genetic predisposition of SLE, association of FcgammaRIIa-H131R, IIb-I232T, IIIa-F176V and IIIb-NA1/NA2 (HNA-1a/1b) polymorphisms with SLE was analyzed in the Thai population, using case-control association analysis. FcgammaRIIb-232T/T and IIIb-NA2/NA2 genotypes were associated with SLE with the odds ratio of 2.55. Genotype relative risk analysis revealed significant association of IIb-232T/T and IIIb-NA2/NA2, and a tendency of association of the IIIa-176F/F genotype. Moreover, carriers of FcgammaRIIa-131R were significantly increased in patients with lupus nephritis. Significant linkage disequilibrium was present among FcgammaRIIb, IIIa and IIIb, and two-locus analyses suggested that the tendency of association of FcgammaRIIIa could derive from linkage disequilibrium with IIb and IIIb. These results provided evidence that FcgammaR polymorphisms may be an important predisposing factor also in Thais in a complex manner.

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