Initiation of allelic exclusion by stochastic interaction of Tcrb alleles with repressive nuclear compartments.

Studies of antigen-receptor loci have linked directed monoallelic association with pericentromeric heterochromatin to the initiation or maintenance of allelic exclusion. Here we provide evidence for a fundamentally different basis for T cell antigen receptor-beta (Tcrb) allelic exclusion. Using three-dimensional immunofluorescence in situ hybridization, we found that germline Tcrb alleles associated stochastically and at high frequency with the nuclear lamina or with pericentromeric heterochromatin in developing thymocytes and that such interactions inhibited variable-to-diversity-joining (V(beta)-to-D(beta)J(beta)) recombination before beta-selection. The introduction of an ectopic enhancer into Tcrb resulted in fewer such interactions and impaired allelic exclusion. We propose that initial V(beta)-to-D(beta)J(beta) recombination events are generally monoallelic in developing thymocytes because of frequent stochastic, rather than directed, interactions of Tcrb alleles with repressive nuclear compartments. Such interactions may be essential for Tcrb allelic exclusion.

Risks Associated With Lentiviral Vector Exposures and Prevention Strategies.

Lentiviral vectors (LVVs) are powerful genetic tools that are being used with greater frequency in biomedical laboratories and clinical trials. Adverse events reported from initial clinical studies provide a basis for risk assessment of occupational exposures, yet many questions remain about the potential harm that LVVs may cause. We review those risks and provide a framework for principal investigators, Institutional Biosafety Committees, and occupational health professionals to assess and communicate the risks of exposure to staff. We also provide recommendations to federal research and regulatory agencies for tracking LVV exposures to evaluate long-term outcomes. U.S. Food and Drug Administration approved antiviral drugs for HIV have theoretical benefits in LVV exposures, although evidence to support their use is currently limited. If treatment is appropriate, we recommend a 7-day treatment with an integrase inhibitor with or without a reverse transcriptase inhibitor within 72 hours of exposure.

Guidelines for Biosafety Training Programs for Workers Assigned to BSL-3 Research Laboratories.

The Guidelines for Biosafety Training Programs for Workers Assigned to BSL-3 Research Laboratories were developed by biosafety professionals who oversee training programs for the 2 national biocontainment laboratories (NBLs) and the 13 regional biocontainment laboratories (RBLs) that participate in the National Institute of Allergy and Infectious Diseases (NIAID) NBL/RBL Network. These guidelines provide a general training framework for biosafety level 3 (BSL-3) high-containment laboratories, identify key training concepts, and outline training methodologies designed to standardize base knowledge, understanding, and technical competence of laboratory personnel working in high-containment laboratories. Emphasis is placed on building a culture of risk assessment-based safety through competency training designed to enhance understanding and recognition of potential biological hazards as well as methods for controlling these hazards. These guidelines may be of value to other institutions and academic research laboratories that are developing biosafety training programs for BSL-3 research.

Enforcing order within a complex locus: current perspectives on the control of V(D)J recombination at the murine T-cell receptor alpha/delta locus.

V(D)J recombination proceeds according to defined developmental programs at T-cell receptor (TCR) and immunoglobulin loci as a function of cell lineage and stage of differentiation. Although the molecular details are still lacking, such regulation is thought to occur at the level of accessibility of chromosomal recombination signal sequences to the recombinase. The unique and complex organization of the TCRalpha/delta locus poses intriguing regulatory challenges in this regard: embedded TCRalpha and TCRdelta gene segments rearrange at distinct stages of thymocyte development, there is a highly regulated progression of primary followed by secondary rearrangements involving Jalpha segments, and there are important developmental constraints on V gene segment usage. The locus therefore provides a fascinating laboratory in which to explore the basic mechanisms underlying developmental control. We provide here a current view of cis-acting mechanisms that enforce the TCRalpha/delta locus developmental program, and we emphasize the unresolved issues that command the attention of our and other laboratories.

Monocyte response to Th1 stimulation and effector function toward human mesangial cells are not impaired in patients with lupus nephritis.

Monocytes/macrophages activated by Th1 stimulation such as interferon-gamma (IFN-gamma) and CD40 ligand (CD40L) infiltrate the kidney and play a critical role in the progression of lupus nephritis (LN). We examined the monocyte response to Th1 stimulation and their effector function toward activating renal resident cells in patients with LN. Following stimulation with IFN-gamma granulocyte macrophage-colony stimulating factor (GM-CSF)/recombinant CD40L the production of tumor necrosis factor-alpha and IL-12 p70 by PBMC was significantly higher in LN patients. In coculture experiments employing activated monocytes and human mesangial cells, there was a trend toward higher monocyte chemoattractant protein-1 production by lupus monocytes compared to normal controls. Basal expression of CD40, ICAM-1, and STAT-1 was significantly higher in monocytes from LN patients, suggesting ongoing activation. Monocyte response to IFN-gamma, as accessed by intercellular adhesion molecule-1 upregulation and phosphorylation of STAT-1, was comparable between the two groups. Thus, in contrast to earlier reports, Th1-dependent monocyte activation is not impaired. In this disease activated monocytes appear to be fully capable of inducing renal injury.