The added value of free preparatory activities for widening access to medical education: a multi-cohort study.

BACKGROUND: Medical schools are reported to be less accessible to students with non-traditional backgrounds. These students face barriers when applying for and transitioning to medical school, which may be reduced by offering free preparatory activities. By equalizing access to resources, these activities are expected to reduce disparities in selection outcomes and early academic performance. In the present study, four free institutionally-provided preparatory activities were evaluated by comparing the demographic composition of participating and non-participating applicants. Additionally, the association between participation and selection outcomes and early academic performance was investigated for subgroups (based on sex, migration background and parental education). METHODS: Participants were applicants to a Dutch medical school in 2016-2019 (N = 3592). Free preparatory activities included Summer School (N = 595), Coaching Day (N = 1794), Pre-Academic Program (N = 217), and Junior Med School (N = 81), supplemented with data on participation in commercial coaching (N = 65). Demographic compositions of participants and non-participants were compared using chi-squared tests. Regression analyses were performed to compare selection outcomes (curriculum vitae [CV], selection test score, probability of enrolment) and early academic performance (first-course grade) between participants and non-participants of demographic subgroups, controlling for pre-university grades and participation in other activities. RESULTS: Generally, no differences in sociodemographic compositions of participants and non-participants were found, but males participated less often in Summer School and Coaching Day. Applicants with a non-Western background participated less often in commercial coaching, but the overall participation rate was low and participation had negligible effects on selection outcomes. Participation in Summer School and Coaching Day were stronger related with selection outcomes. In some cases, this association was even stronger for males and candidates with a migration background. After controlling for pre-university grades, none of the preparatory activities were positively associated with early academic performance. CONCLUSIONS: Free institutionally-provided preparatory activities may contribute to student diversity in medical education, because usage was similar across sociodemographic subgroups, and participation was positively associated with selection outcomes of underrepresented and non-traditional students. However, since participation was not associated with early academic performance, adjustments to activities and/or curricula are needed to ensure inclusion and retention after selection.

Selection tools and student diversity in health professions education: a multi-site study.

Student diversity in health professions education (HPE) can be affected by selection procedures. Little is known about how different selection tools impact student diversity across programs using different combinations of traditional and broadened selection criteria. The present multi-site study examined the chances in selection of subgroups of applicants to HPE undergraduate programs with distinctive selection procedures, and their performance on corresponding selection tools. Probability of selection of subgroups (based on gender, migration background, prior education, parental education) of applicants (N = 1935) to five selection procedures of corresponding Dutch HPE undergraduate programs was estimated using multilevel logistic regression. Multilevel linear regression was used to analyze performance on four tools: prior-education grade point average (pe-GPA), biomedical knowledge test, curriculum-sampling test, and curriculum vitae (CV). First-generation Western immigrants and applicants with a foreign education background were significantly less likely to be selected than applicants without a migration background and with pre-university education. These effects did not vary across programs. More variability in effects was found between different selection tools. Compared to women, men performed significantly poorer on CVs, while they had higher scores on biomedical knowledge tests. Applicants with a non-Western migration background scored lower on curriculum-sampling tests. First-generation Western immigrants had lower CV-scores. First-generation university applicants had significantly lower pe-GPAs. There was a variety in effects for applicants with different alternative forms of prior education. For curriculum-sampling tests and CVs, effects varied across programs. Our findings highlight the need for continuous evaluation, identifying best practices within existing tools, and applying alternative tools.

Hepatitis B virus suppresses the functional interaction between natural killer cells and plasmacytoid dendritic cells.

Natural killer cells (NK) are one of the key players in the eradication and control of viral infections. Infections with the hepatitis B virus (HBV) may lead to persistence in a subgroup of patients, and impaired NK cell functions have been observed in these patients. Crosstalk with other immune cells has been shown to modulate the function of NK cells. We studied the functional crosstalk between NK cells and plasmacytoid dendritic cell (pDC) and its modulation by HBV. Healthy human peripheral blood-derived NK cells and pDC were purified and cocultured in the presence or absence of HepG2.2.15-derived HBV under various in vitro conditions. The functionality of NK cells was assessed by evaluation of activation markers, cytokine production and cytotoxicity of carboxyfluorescein succinimidyl ester-labelled K562 target cells by flow cytometry or immunoassays. Additionally, the crosstalk was examined using NK and pDC from patients with chronic HBV. The activation of NK cells in cocultures with pDC, as demonstrated by CD69, CD25 and HLA-DR, was not affected by the presence of HBV. Similarly, when cocultured with pDC, the cytotoxic potential of NK cells was not influenced by HBV. However, HBV significantly inhibited pDC-induced IFN-γ production by NK cells both in the presence and in the absence of CpG. As HBV did not affect cytokine-induced IFN-γ production by NK cells cultured alone, the suppressive effect of HBV on NK cell function was mediated via interference with pDC-NK cell interaction. In contrast to other viruses, HBV does not activate pDC-NK cell interaction but inhibits pDC-induced NK cell function. In parallel with NK cells of patients with chronic HBV, which show diminished cytokine production with normal cytotoxicity, HBV specifically suppressed pDC-induced IFN-γ production by NK cells without affecting their cytolytic ability. These data demonstrate that HBV modulates pDC-NK cell crosstalk, which may contribute to HBV persistence.

Branched oligosaccharide structures on HBV prevent interaction with both DC-SIGN and L-SIGN.

Hepatitis B virus (HBV) is a DNA virus that infects the liver as primary target. Currently, a high affinity receptor for HBV is still unknown. The dendritic cell specific C-type lectin DC-SIGN is involved in pathogen recognition through mannose and fucose containing carbohydrates leading to the induction of an anti-viral immune response. Many glycosylated viruses subvert this immune surveillance function and exploit DC-SIGN as a port of entry and for trans-infection of target cells. The glycosylation pattern on HBV surface antigens (HBsAg) together with the tissue distribution of HBV would allow interaction between HBV and DC-SIGN and its liver-expressed homologue L-SIGN. Therefore, a detailed study to investigate the binding of HBV to DC-SIGN and L-SIGN was performed. For HCV, both DC-SIGN and L-SIGN are known to bind envelope glycoproteins E1 and E2. Soluble DC-SIGN and L-SIGN specifically bound HCV virus-like particles, but no interaction with either HBsAg or HepG2.2.15-derived HBV was detected. Also, neither DC-SIGN nor L-SIGN transfected Raji cells bound HBsAg. In contrast, highly mannosylated HBV, obtained by treating HBV producing HepG2.2.15 cells with the alpha-mannosidase I inhibitor kifunensine, is recognized by DC-SIGN. The alpha-mannosidase I trimming of N-linked oligosaccharide structures thus prevents recognition by DC-SIGN. On the basis of these findings, it is tempting to speculate that HBV exploits mannose trimming as a way to escape recognition by DC-SIGN and thereby subvert a possible immune activation response.

Quantification of dendritic cell subsets in human renal tissue under normal and pathological conditions.

Dendritic cells (DCs) play critical roles in immune responses and can be distinguished in two major subsets, myeloid and plasmacytoid DCs. Although the presence of DC in all peripheral organs, including the kidney, has been well documented, no accurate estimates of DC subsets in human kidneys have been reported. This study shows a detailed analysis of DC subsets in cryosections of human renal tissue. The cortex of normal kidneys contains at least two different HLA-DR(+) myeloid DC subtypes characterized by BDCA-1(+)DC-SIGN(+) and BDCA-1(+)DC-SIGN(-). The staining for DC-SIGN completely overlapped with CD68 in the renal interstitium. Unexpectedly, BDCA-2(+)DC-SIGN(-) plasmacytoid DCs are also abundantly present. Both subsets are located in the tubulo-interstitium often with a high frequency around, but rarely observed within glomeruli. Quantification of BDCA-1(+), DC-SIGN(+), and BDCA-2(+) cells in normal human renal tissue (pretransplant biopsy living donors; n=21) revealed that BDCA-1 is about four times as frequently present as BDCA-2. A preliminary cross-sectional analysis of DC in diseased kidneys, including rejection and immunoglobulin A nephropathy, revealed that the number of DC as well as their anatomical distribution might change under pathophysiological conditions. In conclusion, we show that human kidneys contain a dense network of myeloid and plasmacytoid DCs and provide the tools for phenotyping and enumeration of these cells to better understand interindividual differences in immune responses.

Maturation-resistant dendritic cells induce hyporesponsiveness in alloreactive CD45RA+ and CD45RO+ T-cell populations.

Dendritic cells (DCs) play a crucial role in the induction of antigen-specific immunity and tolerance. Considering in vivo application of DCs prior to human organ transplantation, a protocol to develop tolerogenic DCs that not only induce unresponsiveness in naive (CD45RA+) T cells, but also in alloreactive memory (CD45RO+) T cells is required. The present study shows that dexamethasone (Dex) alters the differentiation of human monocyte-derived DCs. DexDCs cocultured with allogeneic CD4+ T cells induced low proliferating and low IFNgamma producing T cells. This is caused by lack of both costimulation via CD28 and hampered production of a soluble factor, as well as additional active suppression via B7-H1 and IL-10. T cells primed by DexDCs demonstrated hyporesponsiveness upon restimulation with mature DCs seemingly via the induction of anergy, since these cells showed no enhanced apoptosis and only a limited suppressive capacity. Interestingly, not only cocultures of allogeneic CD45RA+, but also of CD45RO+ T cells with DexDCs rendered T-cell populations hyporesponsive to restimulation with mature DCs. The finding that also alloreactive memory T cells can be regulated supports the rationale of cell-based therapies to obtain allograft-specific tolerance in transplant recipients.

Rapamycin induces apoptosis in monocyte- and CD34-derived dendritic cells but not in monocytes and macrophages.

Rapamycin (Rapa), a recently introduced immunosuppressive drug, seems to be effective in preventing acute allograft rejection. Although its antiproliferative effect on T lymphocytes has been investigated extensively, its effect on the initiators of the immune response, the dendritic cells (DCs), is not known. Therefore, the effect of Rapa on monocyte- (mo-DCs) and CD34(+)-derived DCs in vitro but also on other myeloid cell types, including monocytes and macrophages, was examined. The present study shows that Rapa does not affect phenotypic differentiation and CD40L-induced maturation of mo-DCs. However, Rapa dramatically reduced cell recovery (40%-50%). Relatively low concentrations of Rapa (10(-9) M) induced apoptosis in both mo-DCs and CD34(+)-derived DCs, as visualized by phosphatidylserine exposure, nuclear condensation and fragmentation, and DNA degradation. In contrast, Rapa did not affect freshly isolated monocytes, macrophages, or myeloid cell lines. The sensitivity to Rapa-induced apoptosis was acquired from day 2 onward of mo-DC differentiation. Rapa exerts its apoptotic effect via a reversible binding to the cytosolic receptor protein FKBP-12, as demonstrated in competition experiments with FK506, which is structurally related to Rapa. Partial inhibition of Rapa-induced apoptosis was obtained by addition of ZVAD-fmk, which implies caspase-dependent and caspase-independent processes. The fact that Rapa exerts a specific effect on DCs but not on monocytes and macrophages might contribute to the unique actions of Rapa in the prevention of allograft rejection and other immune responses.

Immunological function of tubular epithelial cells: the functional implications of CD40 expression.

Tubulo-interstitial inflammation in the kidney is characterized by the presence of activated T cells. Both by the local production of cytokines, as well as by direct cell-cell interactions, these activated T cells might affect the immune and inflammatory response. Recently it has been demonstrated that these kidney-infiltrating T cells express CD40 ligand and that tubular epithelial cells (TECs) express CD40. In the present review we will discuss the potential implications of CD40-CD40L interactions for the activation of TECs and its immunological function.

The effect of calcineurin inhibitors and corticosteroids on the differentiation of human dendritic cells.

Corticosteroids and the calcineurin inhibitors cyclosporin A (CsA) and FK506 have been studied extensively regarding their effects on T lymphocytes, but their effects on dendritic cells (DC) are relatively unknown. Monocytes are one of the precursors of DC that differentiate into CD14-CD1a+ immature DC upon culture with IL-4 and GM-CSF. The presence of CsA or FK506 during differentiation did not affect DC development. In contrast, the presence of corticosteroids, either dexamethasone (Dex) or prednisolone (Pred), for as little as the first 48 h of culture blocked the generation of immature DC. Dex-DC were unresponsive to signals inducing maturation (CD40 ligand, lipopolysaccharide), as demonstrated by the absence of CD83, CD80/CD86 and HLA-DR up-regulation and their strongly reduced T cell stimulatory capacity. Furthermore, Dex-DC showed a decreased CD40 ligand-induced IL-6 and TNF-alpha production, a complete block in IL-12p40 production, while IL-10 production was unaffected. CsA-DC and FK506-DC showed a partial reduction in the production of TNF-alpha, whereas all other functional activities appeared to be similar to control DC. These data show that, when compared to calcineurin inhibitors, corticosteroids have a unique and profound inhibitory effect on the generation and function of DC.

Synergistic effect of interleukin-1 and CD40L on the activation of human renal tubular epithelial cells.

BACKGROUND: Renal tubular epithelial cells are a central cell type in tubulointerstitial inflammation because they can produce inflammatory mediators such as cytokines and chemokines. Several signals derived from either monocytes or activated T cells have been reported to regulate the activation of tubular epithelial cells. We studied this regulation in more detail by combined treatment with CD40 ligand and the proinflammatory cytokine interleukin-1 (IL-1) in vitro. METHODS: The regulation of cytokine and chemokine production was studied in primary cultures of human proximal tubular epithelial cells (PTECs). PTECs were activated by coculture with CD40L-transfected murine fibroblasts in combination with recombinant human cytokines. The production of IL-6, IL-8, monocyte chemoattractant protein-1 (MCP-1), and RANTES were measured by specific enzyme-linked immunosorbent assay. RESULTS: The combined activation of PTECs with CD40L and IL-1 resulted in strong synergistic effects on the production of IL-6, IL-8, and RANTES, whereas only an additive stimulation of MCP-1 production was observed. The effects were specific for IL-1 and could be neutralized by the addition of the IL-1R antagonist. Both IL-1alpha and IL-1beta showed similar effects on cytokine production by PTECs. The effects of IL-1 were dose dependent, and kinetic experiments showed that synergistic effects were observed after 24 hours of activation and remained present for at least five days. Reverse transcription-polymerase chain reaction analysis showed that human PTECs could express both IL-1alpha and IL-1beta. The activation of PTECs with IL-1 resulted in an up-regulation of CD40 expression on these cells. CONCLUSIONS: A complex network of regulation exists for the production of cytokines and chemokines by PTECs. The combined treatment results in strong synergistic effects on IL-6, IL-8, and RANTES production. This strengthens the potential role of tubular epithelial cells in inflammatory responses within the kidney.

Transactivation of classical and nonclassical HLA class I genes through the IFN-stimulated response element.

The IFN-stimulated response element (ISRE) is an important conserved cis-acting regulatory element in the promoter of MHC class I genes, but displays considerable locus-specific nucleotide variation. In this report, the putative ISREs of classical and nonclassical HLA class I genes were investigated for their contribution to MHC class I transactivation. It is shown that IFN-gamma induced MHC class I transactivation through the ISRE of HLA-A, HLA-B, HLA-C, and HLA-F. This is congruent with the binding of IFN regulatory factor-1 to the ISREs of these loci upon IFN-gamma treatment. Sp1 was shown to bind to the CG-rich sequences in the ISRE regions of HLA-B, HLA-C, and HLA-G. The putative E box 5' of the ISRE in most HLA-B alleles was shown to bind the upstream stimulatory factors (USF) 1 and 2. The Sp1 and USF binding sites did not influence IFN-gamma-induced transactivation. However, the USF binding site played a suppressive role in the constitutive expression of HLA-B. The locus-specific transcriptional control through the ISRE could be an important mechanism in the differential regulation of classical and nonclassical MHC class I expression, which determines adequate Ag presentation upon pathogenic challenge.

Exhaled nitric oxide (NO) is reduced shortly after bronchoconstriction to direct and indirect stimuli in asthma.

Exhaled NO is increased in patients with asthma and may reflect disease severity. We examined whether the level of exhaled NO is related to the degree of airway obstruction induced by direct and indirect stimuli in asthma. Therefore, we measured exhaled NO levels before and during recovery from histamine and hypertonic saline (HS) challenge (Protocol 1) or histamine, adenosine 5'-monophosphate (AMP), and isotonic saline (IS) challenge (Protocol 2) in 11 and in nine patients with mild to moderate asthma, respectively. The challenges were randomized with a 2-d interval. Exhaled NO and FEV1 were measured before and at 4, 10, 20, and 30 min after each challenge. NO was measured during a slow VC maneuver with a constant expiratory flow of (0.05 x FVC)/s against a resistance of 1 to 2 cm H2O. Baseline exhaled NO levels were not significantly different between study days in Protocol 1 (mean +/- SD: 4.8 +/- 1.8 ppb [histamine] versus 5.4 +/- 2.1 ppb [HS], p = 0.4) or in Protocol 2 (7.9 +/- 4.7 ppb [histamine], 8.3 +/- 5.2 ppb [AMP], and 7.2 +/- 3.7 ppb [IS], p = 0.7). A significant reduction in exhaled NO was observed directly after HS (mean +/- SEM: 39.2 +/- 3.9 %fall) and AMP challenge (32.3 +/- 7.3 %fall) (MANOVA, p < 0.001), respectively, whereas exhaled NO levels tended to decrease after histamine challenge. Isotonic saline challenge did not induce changes in exhaled NO (p = 0.7). There was a positive correlation between %fall in FEV1 and the %fall in exhaled NO after histamine, HS, and AMP challenge as indicated by the mean slope of the within-subject regression lines (p <= 0.04). We conclude that acute bronchoconstriction, as induced by direct and indirect stimuli, is associated with a reduction in exhaled NO levels in asthmatic subjects. This suggests that airway caliber should be taken into account when monitoring exhaled NO in asthma.