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Jak3, a member of the Janus tyrosine kinase family is an intracellular kinase functionally coupled to cytokine receptors that share a common gamma chain (gamma c). Defects in the gamma c or Jak3 result in T-B + severe combined immunodeficiency (SCID). In order to clarify discrepancies between earlier reported genomic organisations of human JAK3, the present study was undertaken to redefine its whole exon-intron structure. The genomic structure of human JAK3 consists of 23 exons and 22 introns, and shows strong homology with the organisation of the murine JAK3 locus. The exon-intron sequences provided in this report can be used to facilitate the identification of new Jak3-deficient SCID patients, including prenatal diagnosis.

The liver has been presumed to be the main source of complement deposited in inflammatory lesions such as in glomerulonephritis. In a previous study, however, it was demonstrated that renal tubular cells synthesize C3 in vitro. Furthermore, it was shown by others that C4 gene transcripts were detectable in situ in renal tubular cells. Therefore studies were initiated to investigate the synthesis of C4 by proximal tubular epithelial cells (PTEC) in vitro. Biosynthetic labeling experiments showed de novo synthesis of C4 by PTEC. The synthesis of C4 by PTEC and its regulation by IFN-gamma was fully inhibitable by the addition of cycloheximide, indicating that protein synthesis is required for an increase in C4 secretion. Addition of increasing concentrations of IFN-gamma enhanced the production of C4 by PTEC in a dose dependent fashion, with a 2.5-fold maximum. Kinetic experiments demonstrated higher levels of C4 production when stimulated with IFN-gamma for up to 72 hours. The hemolytic activity of C4 present in culture supernatants of PTEC decreased during the culture period as assessed by hemolytic titration. Northern blot analysis showed no enhancement of C4 mRNA in IFN-gamma treated PTEC, indicating that IFN-gamma regulates C4 production at a post-transcriptional level. Antibody blocking experiments confirmed that regulation of C4 production was directly mediated by IFN-gamma. From this study it was concluded that renal cells are able to synthesize complement components that could possibly play a role in inflammatory responses evolving in the kidney.

Using cDNA clones H-19 and H-46, we have shown previously that three different mRNA species (4.3 kb, 1.8 kb and 1.4 kb) for complement factor H are expressed constitutively in human liver. Here we report data suggesting that the expression of these different factor-H mRNA species is regulated by tissue-specific control mechanisms. Total RNA and poly(A)-enriched RNA from various human tissues (heart, lung, temporal cortex, kidney, spleen, bone marrow and muscle) various cell lines (HepG2, HepG3, HepG4, Hep3B, H-4, Jurkat, Molt4, H-9, KHos24Os, A-431, U937, Mono Mac 6 and Raji) and from primary cultures of peripheral blood monocytes, fibroblasts and human umbilical vein endothelial cells (HUVEC) were investigated for the expression of factor-H mRNA. In RNA preparations from extrahepatic tissue, factor-H mRNA was only detected in biopsies from the lung. Using 20 micrograms total RNA isolated from all 13 cell lines it was not possible to detect any factor-H mRNA, while mRNA for factor H was expressed in monocytes, HUVEC and fibroblasts. When expressed in extrahepatic tissues, only the 4.3-kb and the 1.8-kb mRNA species were detected, while the 1.4-kb mRNA is expressed abundantly in liver. Interferon-gamma did not induce the expression of factor-H mRNA in any of the cell lines tested. On the other hand, tumour necrosis factor-alpha induced the expression of the 4.3-kb mRNA species in U937 cells. In HUVEC and fibroblasts the relative quantities of the 4.3-kb and the 1.8-kb mRNA species and the regulatory effects of interferon-gamma, interleukin-1, dexamethasone and retinoic acid on their expression showed significant tissue specificity.