Electrotransfection of anchorage-dependent mammalian cells

Reversible electropermeabilization (or electroporation) of cell membranes is a very efficient method for intracellular delivery of xenomolecules, particularly of DNA. In the case of anchorage-dependent cells, however, enzymatic or mechanical detachment from the substratum is required prior to electropulsing. This can damage the plasma membrane and lead to low transfection yields. Here we present an efficient method for in situ electroporation of mammalian cells while they are attached to a solid substratum. For this purpose an electroporation chamber was constructed that housed a cell culture insert with a cell monolayer grown on a porous filter. By real-time monitoring the transmonolayer resistance, the field pulse parameters resulting in transient and reversible permeabilization of cell membranes were determined for two adherent cell lines, which were found to differ markedly in their sensitivity to electropulsing. Based on the transmonolayer resistance data, the pulsing conditions for optimum electrotransfection of two murine cell lines with plasmid DNA could be established in a very short time. The transfection yield and gene expression were significantly higher in cell monolayers facing the cathode compared to those exposed to field pulses of the reverse direction. This might be due to contribution of the electrophoresis to the translocation of the polyanionic plasmid DNA across the electropermeabilized cell membrane. The experimental setup presented here appears to be a promising tool not only for rapid optimization of in situ electrotransfection of anchorage-dependent cells but also for studying the molecular/biophysical mechanisms of the membrane breakdown and resealing.

Development of thymic and splenic dendritic cell populations from different hemopoietic precursors

The antigen-presenting dendritic cells (DCs) found in mouse lymphoid tissues are heterogeneous. Several types of DCs have been identified on the basis of the expression of different surface molecules, including CD4, CD8alpha, and DEC-205. Previous studies by the authors showed that the mouse intrathymic lymphoid-restricted precursors (lin(-)c-kit(+)Thy-1(low)CD4(low)) can produce DCs in the thymus and spleen upon intravenous transfer, suggesting a lymphoid origin of these DCs. In the current study, the potential for DC production by the newly identified bone marrow (BM) common lymphoid precursors (CLPs), common myeloid precursors (CMPs), and committed granulocyte and macrophage precursors was examined. It was found that both the lymphoid and the myeloid precursors had the potential to produce DCs. All the different DC populations identified in mouse thymus and spleen could be produced by all these precursor populations. However, CLPs produced predominantly the CD4(-)CD8alpha(+) DCs, whereas CMPs produced similar numbers of CD4(-)CD8alpha(+) and CD4(+)CD8alpha(-) DCs, although at different peak times. On a per cell basis, the CLPs were more potent than the CMPs at DC production, but this may have been compensated for by an excess of CMPs over CLPs in BM. Overall, this study shows that the expression of CD8alpha does not delineate the hemopoietic precursor origin of DCs, and the nature of the early precursors may bias but does not dictate the phenotype of the DC product.

Development of dendritic cells in culture from human and murine thymic precursor cells

The earliest T-precursor population in the adult murine thymus can give rise to dendritic cells (DC) in culture if stimulated with a cocktail of cytokines that includes interleukin (IL)-3, but not with cytokine mixes based on granulocyte-macrophage colony stimulating factor (GM-CSF), normally used to generate myeloid-derived DC. This and other evidence led to the proposal that two different lineages of DC exist, one lymphoid-related and the other myeloid-related. To determine whether this selective response to cytokines was restricted to murine DC, early human thymic T-precursors were isolated and their capacity to generate DC in response to various cytokines directly compared to their murine counterparts. In contrast to cultures of murine thymic precursors, CD34+CD1a- lineage marker negative (Lin-) precursor cells from the human thymus proliferated and generated DC with both the IL-3-containing cytokine mix lacking GM-CSF and with GM-CSF based cytokine mixes. These CD34+CD1a-Lin- human precursor cells also gave rise to NK cells under appropriate culture conditions, but produced no granulocyte, monocyte, eosinophil, megakaryocyte or erythroid cells in standard soft-agar colony-forming cell assays. Thus, although apparently lymphoid-restricted, the human thymic DC precursors responded to the myeloid factor GM-CSF as well as to the cytokines selective for murine lymphoid-related DC.

Altogether now? Professional differences in the priorities of primary care groups

BACKGROUND

Little is known about the similarities or differences with which Primary Care Group (PCG) Board members view the relative importance of the three functions with which they are charged, or how representative these views are of local primary care teams in general. This project explores the priorities of medical and nursing PCG Board members in relation to those of local General Practitioners (GPs) and practice nurses they represent.

METHODS

Postal questionnaires were sent to GPs (n=236) and practice nurses (n= 137); structured telephone interviews were carried out with PCG Board members (n=61) in East Sussex, Brighton and Hove.

RESULTS

There are large differences between the views of GPs and those of their nursing colleagues on how PCG Board members should determine priorities in their work. There are also marked differences in the priorities of PCG Boards (of whom the majority are GPs) and non-Board member GPs. Whereas around two-thirds of PCG Board members believe that improving health generally and reducing inequalities in particular are the most important tasks before them, this view is not shared by most GPs in the same localities, who are generally more concerned about commissioning services. There is some doubt among GPs generally about the suitability of PCG Board members as a vehicle for the tasks they have been set, and this doubt is also found among PCG Board members themselves.

CONCLUSIONS

The priorities of PCG Board members of different disciplines need to be aligned in order that they have a clear focus on the tasks before them. PCG Boards must also have priorities that are consistent with the local practitioners who elected them. Effective systems of communication will need to be developed between PCG Board members, Health Authorities and individual Primary Care Groups. Local flexibility is essential to the success of Primary Care Groups, but tackling inequalities in health must always be at the forefront of their role.

Starting smoking: girls' explanations of the influence of peers

A questionnaire survey of cigarette smoking completed in six secondary schools by 4773 pupils aged 11-16 years included five items concerning the circumstances of smoking initiation: (1) age at first cigarette; (2) source of supply; (3) location of first smoke; (4) persons present; and (5) perceived degree of coercion. Although there was a highly significant gender difference on the item concerning age at first cigarette, with the average for boys lower than that for girls, the remaining items showed no gender effects. In order to explore further the reasons for the observed higher prevalence of cigarette smoking among teenage girls compared to boys, 33 focus groups were undertaken with girls in Years 7 and 9. These qualitative data provide evidence of the social representations of different groups and of smoking and non-smoking identities. Any understanding of smoking among girls needs to take account the dynamics of girls' membership in groups of never, experimental and regular smokers in determining subsequent smoking behaviour.