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Unlike other loci, only one allele of the immunoglobulin genes in a B cell is used to produce antibodies. Skok and colleagues (p 31) investigate how such 'allelic exclusion' is enforced. The Igh genes temporarily contract, which juxtaposes distal VH segments with downstream DHJH sequences. Signaling through the pre-BCR triggers loss of this close apposition, precluding further rearrangements with distal VH regions. Confocal image shows in situ nuclear hybridization signals of the looped Igh locus. Artwork by Lewis Long.
The fourth EMBO workshop on “Lymphocyte antigen receptor and coreceptor signaling” gathered immunologists to share key findings, new questions and emerging trends in the field of cell signaling.
Dendritic cells have the unique capacity of processing soluble exogenous proteins for presentation to killer T lymphocytes. Now Cresswell and associates show that this is possible because pinocytosed material gains access to the perinuclear endoplasmic reticulum of dendritic cells.
The signaling pathways distinguishing positive and negative thymic selection are critical for establishing T cell immunity and tolerance. The kinase MINK might be an important component that differentiates these two events.
When confronted with a pathogen, the immune system must develop the appropriate type of immune response. Recent work provides new insight into how regulated gene activation and silencing occurs in helper T cells.
Human skin is surprisingly resistant to colonization by Escherichia coli, a prevalent commensal bacterium of the gut flora. An 11-kDa Zn2+-binding protein, psoriasin, is identified as the principal E. coli–bactericidal factor present at the surface of human skin.