Hospital restructuring initiatives in Canada.

OBJECTIVES: Recent changes in the organization, staffing, and utilization of acute hospitals in Canada are reviewed with regard to the potential implications for quality of care, national nurse workforce requirements, and research. METHODS: Available national and selected provincial data and trends in hospital utilization, capacity, and staffing are synthesized. RESULTS: Health system reform in Canada has resulted in lower utilization of acute inpatient resources, excess hospital capacity, and increased budgetary constraints in the hospital sector. In response, there is widespread hospital restructuring, which includes modifications in nurse staffing ratios and skill mix. Little is known about the potential impact of these changes on patient outcomes. From a workforce perspective, changes in the hospital sector have reduced demand for registered nurses but nursing schools have not modified enrollments. As a result, new graduates are experiencing difficulty obtaining registered nurse positions. CONCLUSIONS: Research should be undertaken to evaluate the impact of changes in the organization and staffing of hospitals on patient outcomes, and on the future requirements for nurses.

Hyper-reactivity of mouse CD45RA- T cells.

Mouse CD4 T cells have been partitioned into CD45RA and CD45RA- subpopulations by means of the monoclonal antibody 14.8. The CD45RA- subpopulation proliferated more actively and generated more interleukin-4 (IL-4) in response to stimulation with anti-CD3 antibody and phytohemagglutinin, and more IL-2 in response to anti-CD3. This subpopulation is therefore hyper-reactive to these polyclonal stimulators, but does not show the bias towards T helper type 2 activity that has been found in studies with other related CD45 isoforms. No evidence of suppression was obtained by comparing proliferation of CD45RA- cells in the presence and absence of CD45RA cells. Thus mouse CD4 T cells behave in these respects similarly to those of man, as is evident in a brief review of the quiescence-activation-quiescence cycle in the two species.

Memory in helper T cells of minor histocompatibility antigens, revealed in vivo by alloimmunizations in combination with Thy-1 antigen.

A cooperative antibody response in which T helper (Th) cells recognize minor histocompatibility antigens (mha) and B cells recognize Thy-1 antigen, is used to explore memory in the T cell compartment. In contrast to B cell memory, Th memory reaches a plateau rapidly, although Th memory of Thy-1 itself (or an associated antigen) behaves exceptionally in this respect. The plateau then extends over several weeks at least. Single mha, among them H-Y, generate detectable memory. Incompatible H-2 antigens, including class I antigens on their own, inhibit this response through what appears to be a mechanism of intracellular antigenic competition. Antigen presentation in this system is by host cells, as judged by lack of donor-specific restriction. Memory resides in both the CD45RA+ and CD45RA- compartments, although the majority of memory Th cells have the latter phenotype.

Antigen presentation by dendritic cells provides optimal stimulation for the production of interleukin (IL) 2, IL 4 and interferon-gamma by allogeneic T cells.

Previous studies have shown that dendritic cells are the most potent inducers of T cell proliferation in vitro and that this is reflected in the release of interleukin (IL) 2 into culture supernatants during dendritic cell-T cell interaction. However, the role of the dendritic cells, and, indeed, of the antigen-presenting step, has not yet been explored with respect to other T cell-derived cytokines, in either a qualitative or relative fashion. In this study, therefore, we have examined the comparative role of different antigen-presenting cells (APC) as inducers of T cell cytokine release in allogeneic responses. We have confirmed that dendritic cells are the most effective inducers for IL2 and have shown that this is true not only in primary alloresponses, but also in alloresponder T cells maintained for extended periods and then rechallenged. Dendritic cells were also the most potent inducers of IL3 and interferon-gamma (IFN-gamma) in primary cultures. No IL4 was demonstrable irrespective of the type of presenting cells used, and both tissue macrophages and dendritic cells can induce synthesis of IL6. Likewise, in secondary alloresponses both dendritic cells and to a lesser extent tissue macrophages induce release of IL3, no IL4 is detectable, and activated macrophages and B cells raise IFN-gamma levels in the supernatants albeit to a lower concentration than that seen when dendritic cells are used as stimulators. The results were similar in the tertiary alloresponse except that (a) IL4 was now detectable in the supernatants but only where dendritic cells had been used as APC, and (b) both resting and activated macrophages induced IL2 and IFN-gamma. By the eighth cycle of allostimulation there is negligible IL2. Dendritic cells, tissue macrophages and activated B cells constitute a hierarchy of APC for IL3, IFN-gamma and IL4. These findings therefore demonstrate the role of dendritic cells as potent in vitro inducers of IL3, IL4 and IFN-gamma synthesis as well as of IL2.

CD45RA antibodies split the CD3bright T cell subset.

Thymocyte subsets have been well characterized on the basis of CD4 and CD8 antigen expression. Recently, the use of anti-CD3 antibodies has allowed more precise phenotyping of these subsets. The most immature T cell precursors are largely CD3-CD4-CD8-, while the most mature are CD3brightCD4+CD8- or CD3brightCD4-CD8+. Moreover, the expression of CD45RA on thymocytes appears to define a progenitor population and may define a continuous lineage of cells. Using a panel of CD45RA antibodies, we have further characterized the CD45RA+ thymocyte population in the murine system. The size of this subset is greatly enhanced in cortisone-treated mice and in sublethally irradiated mice. Moreover, the CD45RA+ population is present early in foetal life and is maintained thereafter. Using three-colour immunofluorescence, we show that (i) while most CD45RA+ cells are present amongst the CD4-CD8- thymocyte subset in the normal thymus, after cortisone treatment or irradiation, all four thymocyte subsets co-express significant amounts of CD45RA. This suggests that not only progenitor cells but also the mature population which can survive such manipulation are CD45RA+; and (ii) a large proportion of CD45RA+ cells are CD3bright and this subset is represented in the thymus at all stages of maturation tested. These data suggest that a proportion of TCR-gamma delta + CD3+ cells in the fetus as well as of TCR-alpha beta+ CD3+ cells in the adult co-express CD45RA.

In the mouse the maturation stage of the peripheral CD4+ CD45RA+ subset is different from that of the CD8+ CD45RA+ subset.

In vitro studies have suggested that the presence of CD45RA on subsets of CD4 and CD8 cells defines naive T cells and that, in response to antigen, CD45RA+ cells become CD45RA- along a differentiation pathway. To test the hypothesis that CD45RA+ cells are naive cells which have just left the thymus, young mice were thymectomized. This would be predicted to lead to a fall in the size of the peripheral pool of CD45RA+ T cells. However, the changes in the size of this pool would also be dependent on the life-span and self renewal capacity of the CD45RA+ T cells in the periphery. Therefore, to test the contribution of the thymus to the peripheral CD45RA+ pool, the percentage of CD45RA+ cells among spleen lymphocyte subsets was studied from 10 days up to 2 years of age in thymectomized and control mice. We also studied the expression of the memory marker CD44 on the CD45RA subsets of CD4 and CD8 cells, as well as the effect of in vitro activation on expression of CD45RA. Our results show that CD8+ CD45RA+ cells are mainly CD44- and their maintenance is dependent on the presence of the thymus. In contrast, the majority of CD4+ CD45RA+ are CD44+ and are not affected by thymectomy. This indicates that the maturation stage of CD8+ CD45RA+ cells is different from that of CD4+ CD45RA+ cells.

The CD45RA molecule is expressed in naive murine CTL precursors but absent in memory and effector CTL.

We have studied the expression of the CD45RA molecule in murine cytotoxic T lymphocytes (CTL) specific for the allogeneic H-2Kb molecule at different stages of differentiation. The CD45RA phenotype of naive H-2Kb-specific CTL precursors has been determined using primary in vitro CTL responses. For the analysis of memory CTL we have immunized mice in vivo followed by restimulation in vitro. We have also determined the CD45RA expression at the CTL effector stage. Our results show that among naive CD8+ T cells both the CD45RA+ and the CD45RA- subpopulations can mount Kb-specific CTL responses. In contrast, memory CTL responses are mediated only by the CD8+ CD45RA+ T cell subpopulation. Similarly, effector CTL are CD8+ CD45RA- while the CD8+ CD45RA+ subpopulation does not exhibit specific cytolytic activity. The data indicate that CD45RA expression changes during CTL differentiation and that memory as well as effector CTL lack this marker.

CD45RA is detected in all thymocyte subsets defined by CD4 and CD8 by using three-colour flow cytometry.

In the mouse, using three-colour flow cytometry, the presence of CD45RA+ cells is demonstrated amongst all of the thymocyte subsets defined by expression of CD4 and CD8, i.e. amongst the double negatives, immature CD8 single positives, double-positive blasts and CD4 and CD8 single positives. This evidence is compatible with the existence of a continuous lineage of T cells expressing CD45RA which would develop from double-negative to mature single-positive T cells.

Anti-CD45RA antibodies increase the proliferation of mouse T cells to phytohemagglutinin through the interleukin 2/interleukin 2 receptor pathway.

We have studied the effect of anti-CD45RA monoclonal antibodies on the proliferation of murine spleen T cells activated with phytohemagglutinin. Antibodies act on both CD8 and CD4 subsets of T cells. They seem to replace a signal normally delivered by accessory cells which would act through the interleukin 2/interleukin 2 receptor pathway.