Genetic defects in downregulation of IgE production and a new genetic classification of atopy

Atopic disorders, such as asthma, eczema and rhinitis, develop due to the interactions between genetic and environmental factors. Atopy is characterized by enhanced IgE responses to environmental antigens. The production of IgE is upregulated by Th2 cytokines, in particular interleukin (IL)-4, and downregulated by Th1 cytokines, in particular interferon (IFN)-γ. In the present review, we present the genetic factors responsible for IgE production and genetic defects in the downregulation (brake) of IgE production, especially in terms of IL-12 and IL-18 signaling, mutations of the IL-12 receptor β2 chain gene and mutations of the IL-18 receptor α chain gene in atopy. Moreover, we newly present a genetic classification of atopy. There are four categories of genes that control the expression of allergic disorders, which include: (i) antigen recognition; (ii) IgE production (downregulation=brake; and upregulation); (iii) the production and release of mediators; and (iv) events on target organs. In the near future, this genetic classification will facilitate the development of tailor-made treatment

Molecular mechanism of a temperature-sensitive phenotype in peroxisomal biogenesis disorder

Peroxisomal biogenesis disorders include Zellweger syndrome and milder phenotypes, such as neonatal adrenoleukodystrophy (NALD). Our previous study of a NALD patient with a marked deterioration by a fever revealed a mutation (Ile326Thr) within a SH3 domain of PEX13 protein (Pex13p), showing a temperature-sensitive (TS) phenotype in peroxisomal biogenesis. Clinical TS phenotypes also have been reported in several genetic diseases, but the molecular mechanisms still remain to be clarified. The immunofluorescent staining with anti-Pex13p antibody also revealed TS phenotype of the I326T mutant protein itself in the patient cells. Protease digestion of the recombinant Pex13p-SH3 domain showed an increase of protease susceptibility, suggesting a problem of mutant protein fold. Conformational analyses against urea denaturation using urea gradient gel electrophoresis or fluorescence emission from tryptophan residue revealed that the mutant protein should be easily unfolded. Far-UV circular dichroism (CD) spectra demonstrated that both wild-type and the mutant protein have antiparallel beta-sheets as their secondary structure with slightly different extent. The thermal unfolding profiles measured by CD showed a marked lower melting temperature for I326T protein compared with that of wild-type protein. Analysis of the protein 3D-structure indicated that the Ile326 should be a core residue for folding kinetics and the substitution of Ile326 by threonine should directly alter the kinetic equilibrium, suggesting a marked increase of the unfolded molecules when the patient had a high fever. Structural analyses of the protein in the other genetic diseases could provide an avenue for better understanding of genotype-phenotype correlation