Class II (or Ia) antigens are highly polymorphic surface molecules which are essential for the cellular interactions involved in the immune response. In man, these antigens are encoded by a complex multigene family which is located in the major histocompatibility complex (MHC) and which comprises up to 12 distinct alpha- and beta-chain genes, coding for the HLA-DR, -DQ and -DP antigens. One form of congenital severe combined immunodeficiency (SCID) in man, which is generally lethal, is characterized by an absence of HLA-DR histocompatibility antigens on peripheral blood lymphocytes (HLA class II-deficient SCID). In these patients, as reported here, we have observed an absence of messenger RNA for the alpha- and beta-chains of HLA-DR, -DQ and -DP, indicating a global defect in the expression of all class II genes. Moreover, the lack of expression of HLA class II mRNAs could not be corrected by gamma-interferon, an inducer of class II gene expression in normal cells. Family studies have established that the genetic defect does not segregate with the MHC. We conclude, therefore, that the expression of the entire family of class II genes is normally controlled by a trans-acting class II regulatory gene which is unlinked to the MHC and which is affected in the patients. This gene controls a function or a product necessary for the action of gamma-interferon on class II genes.

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In vitro modulation of the cytokine network by MTX, increasing Th2 cytokines and decreasing Th1 cytokines, could explain its antiinflammatory and immunoregulatory actions in vivo during the treatment of RA.

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The human major histocompatibility complex class II antigens of the HLA-D are highly polymorphic, surface proteins essential in the cellular interactions necessary for an immune response. The analysis of this polymorphism is crucial for (i) histocompatibility matching for transplantation and (ii) understanding the association between HLA-D and certain important diseases. The polymorphism of certain HLA-D haplotypes may escape detection by current methodologies. Analysis at the genomic level of the polymorphism of one of the HLA-D subregions HLA-DR, using oligonucleotide probes specific for the polymorphic regions, is capable of distinguishing single nucleotide differences. The DRw6 haplotype was analyzed in view of the lack of DRw6 specific sera. On the basis of nucleotide sequence analysis, the DRw6 haplotype consists of at least two subtypes. When analyzed with oligonucleotide probes, this split identifies new polymorphic groups that differ from the DRw6 serological subgroups.