RESUMEN
The identification of factors causing complex diseases contributes to the understanding of their pathophysiology and provides new diagnostic methods and potentially new prevention and treatment strategies. Polymorphic genes functioning in innate and acquired immune mechanisms participate in interindividual and interpopulational differences of susceptibility to many diseases of complex etiology and pathogenesis. Numerous studies have related especially the HLA genes to pathologic autoimmunity, and to the pathogenesis of infectious diseases and cancer. In recent years, the search for additional susceptibility genes has been facilitated by the resources and information generated by genome mapping and diversity analysis. Genes involved in immunity are being identified at an accelerating rate, and the investigation of implications of their variability regarding disease pathogenesis is beginning. Studies of Brazilian populations have especially contributed to recognition of genes modulating susceptibility to infections and their clinical outcome. Since genetic polymorphism differs between populations, the heterogeneity of the Brazilian populations, if properly explored, will add valuable information to the understanding of causes of complex diseases. Conversely, disease studies contribute to knowledge of the evolution and functional implications of genetic polymorphism.