Prevalence, time trends, and correlates of major depressive episode and other psychiatric conditions among young people amid major social unrest and COVID-19 in Hong Kong: a representative epidemiological study from 2019 to 2022

Background

Hong Kong is among the many populations that has experienced the combined impacts of social unrest and the COVID-19 pandemic. Despite concerns about further deteriorations in youth mental health globally, few epidemiological studies have been conducted to examine the prevalence and correlates of major depressive episode (MDE) and other major psychiatric disorders across periods of population-level changes using diagnostic interviews.

Methods

We conducted a territory-wide household-based epidemiological study from 2019 to 2022 targeting young people aged 15-24 years. MDE, generalised anxiety disorder (GAD), panic disorder (PD), and bipolar disorder (BD) were assessed using the Composite International Diagnostic Interview-Screening Scales in 3340 young people. Psychotic disorders were assessed by experienced psychiatrists according to the DSM. Help-seeking patterns were also explored.

Findings

16.6% had any mental disorder (13.7% 12-month MDE, 2.3% BD, 2.1% GAD, 1.0% PD, 0.6% psychotic disorder). The prevalence of MDE increased from 13.2% during period 1 (May 2019-June 2020) to 18.1% during period 2 (July-December 2020), followed by 14.0% during period 3 (January-June 2021) and 13.2% during period 4 (July 2021-June 2022). Different stressors uniquely contributed to MDE across periods: social unrest-related stressors during period 1, COVID-19 stressors during period 2, and personal stressors during periods 3-4. Lower resilience, loneliness, frequent nightmares, and childhood adversity were consistently associated with MDE. Compared to other conditions, those with MDE showed the lowest service utilisation rate (16.7%). Perceiving services to "cost too much" and "talked to friends or relatives instead" were among the major reasons for not seeking help. MDE was also significantly associated with poorer functioning and health-related quality of life.

Interpretation

MDE can be sensitive to population-level changes, although its persistently elevated prevalence across the study period is of concern. Efforts to mitigate their impacts on youth mental health alongside personal risk factors are needed. Further work is required to increase the availability and acceptability of youth-targeted mental health services.

Funding

Food and Health Bureau (HKSAR Government).

Comparison of monocyte enrichment by immuno-magnetic depletion or adherence for the clinical-scale generation of DC

BACKGROUND

DC generated from monocytes have been used for vaccines. We have developed a monocyte enrichment procedure by depleting T and B cells with anti-CD2 and anti-CD19 Abs using the automated Isolex 300i magnetic cell selector for clinical-scale DC generation in gas permeable SteriCell culture bags. We have also compared DC function, yield and purity of DC generated from adherent monocytes using culture bags in a closed system, with DC generated in conventional tissue culture flasks.

METHODS

Monocytes were enriched from normal donor apheresis products using CD2/19 depletion with experimental software on the Isolex 300i (ISO), adherence (AD) to SteriCell bags and to T175 flasks and then cultured for 7 days in serum-free X-VIVO 15 media with GM-CSF and IL-4. Phenotype and dextran uptake were analyzed by flow cytometry and allogeneic MLR was also evaluated.

RESULTS

ISO-DC and AD-DC from SteriCell bags showed similar viability. Higher purity of ISO-DC than AD-DC was measured by forward- and side-scatter flow cytometry. Similar expression of CD1a, CD80, CD86 and CD83 were observed in both ISO-DC and AD-DC. Similar dextran uptake and allo MLR were also observed.

DISCUSSION

These data indicated that functional DC were generated in gas permeable SteriCell culture bags from both ISO- and AD-monocytes in a closed system.

Differential effects of autologous serum on CD34(+) or monocyte-derived dendritic cells

Dendritic cells (DC) with potentially important clinical applications have been generated from human peripheral blood monocytes and CD34(+) cells in the presence of recombinant cytokines granulocyte-macrophage colony-stimulating factor (GM-CSF) + interleukin-4 (IL-4) and GM-CSF + tumor necrosis factor-alpha (TNF-alpha), respectively. Many of the studies generating DC have included fetal calf serum, which is not desirable due to the risk of immune reactions and infectious disease transmission. Additionally, low DC yields have been reported using serum-free media. In this study, we investigate supplementing serum-free media with autologous serum and plasma for DC generation from monocytes and CD34(+) cells. Our results show that functional DC can be reproducibly obtained in the presence of autologous serum using monocytes and CD34(+) cells as the starting populations. However, with the addition of autologous serum, a differential effect is observed in the phenotypic characterization of these culture-derived DC. Monocytes cultured for 7 days in X-VIVO 15 serum-free media in the presence of GM-CSF + IL-4 showed down-regulation of CD14 with increased expression of HLA-DR, mannose receptor, CD80, and CD86, along with highly up-regulated CD1a(+) expression. The addition of autologous serum to serum-free media in monocyte cultures resulted in a dose-dependent decrease in the CD1a(+) expression generating a distinct subset of CD1a(+/-) cells expressing HLA-DR, mannose receptor, CD80, and CD86. Upon stimulation with CD40L cells, both monocyte-derived DC subsets CD1a(+/-) and CD1a(++) were capable of maturation measured by CD83 and CD86 up-regulation. Data suggest the differences in the monocyte-derived DC in serum-free (CD1a(++)) or autologous serum (CD1a(+/-)) supplemented cultures is of a qualitative nature, rather than quantitative. CD1a(+) and CD14(+) cells expressing HLA-DR, mannose receptor, CD80, and CD86 were generated in 7 days from CD34(+) cells in serum-free media. A quantitative effect was obtained when cultures were supplemented with autologous serum, resulting in a significant enhancement of CD34-derived DC generated. These results demonstrate generation of DC from two different starting populations using serum-free media that can be enhanced with the addition of autologous serum. Interestingly, a differential effect was observed in the phenotypic characterization of these culture-derived DC.

Autologous bone marrow transplantation for childhood acute lymphoblastic leukemia: a novel combined approach consisting of ex vivo marrow purging, modulation of multi-drug resistance, induction of autograft vs leukemia effect, and post-transplant immuno- and chemotherapy (PTIC)

In an attempt to reduce the high relapse rate associated with ABMT, five children with high-risk first CR and 19 in second or subsequent CR lacking matched family allogeneic donors underwent ABMT with chemopurged bone marrow utilizing verapamil (VPL), vincristine, and VP-16. Patients were conditioned with TBI, VPL bolus and infusion with VP-16 and cyclophosphamide. The first cohort of patients (n = 4) received only cyclosporin A (CsA). The second cohort (n = 7) received CsA and alpha interferon (total = 11 with post-transplant immunotherapy alone.) The third cohort (n = 13) received CsA and six alternating cycles of alphaIFN and chemotherapy and six additional cycles of chemotherapy (vincristine, VP-16, Ara-C, prednisone) followed by G-CSF (post-transplant immune chemotherapy (PTIC)). The 2-year DFS is 42+/-10% (90% confidence interval (CI) is 26.5-58.5%) and 2-year overall survival is 54+/-10% (90% CI is 37.5-70.5%). Furthermore, patients receiving PTIC (n = 13) vs immunotherapy alone (CsA+/-aIFN) (n = 11) had a substantially better 2 year DFS and OS: 69+/-13% vs 13+/-12% and 85+/-10% vs 25+/-15% (P = 0.008 and P = 0.06, respectively). These results suggest that the use of ABMT with chemopurging, combined with PTIC is well tolerated and may be an alternative new approach in the treatment of a subset of children with high-risk first CR or > or = second CR ALL who lack closely matched family-related allogeneic donors.

Immunological reconstitution and correlation of circulating serum inflammatory mediators/cytokines with the incidence of acute graft-versus-host disease during the first 100 days following unrelated umbilical cord blood transplantation

We investigated early immunological reconstitution and the production of circulating inflammatory mediators and their relationship to aGVHD in children during the first 100 days following unrelated UCBT. Nine patients had an underlying malignant disease (ALL, ANLL), and two, non-malignant diseases (SAA, ALD). The median age was 10 years (range: 1.25-21). Seven of 11 patients were alive by day 100, two died from regimen-related toxicity, and two died from severe aGVHD (grade >/=III). Myeloid engraftment (ANC >/=500/mm3 x 2 days) occurred at a median of 24 days (range: 14-55), while platelet engraftment (platelet count >/=20 000/mm3 untransfused x 7 days) was delayed and occurred at a median of 52 days (range: 33-95). The mean cell dose of CD34+ cells was 3.3 +/- 3.51 x 10(5)/kg, and of CD34+/CD41+ cells was 3.94 +/- 3.99 x 10(4)/kg. Acute GVHD (grade II-IV) developed in seven patients (77%), and severe aGVHD (grade III-IV) developed in five patients (55%). Serum levels of IL-2Ralpha, IL-2, IL-4, IL-7, IL-12, and IFNgamma were not significantly different between patients with grades 0-I aGVHD and patients with grades II-IV aGVHD. Evaluation of immunological reconstitution on day 90 post UCBT demonstrated an early recovery of the absolute numbers of B cells (CD19+) and NK cells (CD3-/CD56+). Immunoglobulin levels for IgG, IgM and IgA remained normal throughout the study period. PMN functional studies demonstrated normal superoxide generation, bacterial killing (BK), and chemotaxis (CTX). However, both helper (CD3+/CD4+) and suppressor (CD3+/CD8+) T cell subsets remained low during the first 100 days post UCBT with mean +/- s.e.m. values of 120 +/- 29/mm3 and 10 +/- 50/mm3, respectively (normal = 900-2860/mm3 (CD3/CD4), normal = 630-1910/mm3 (CD3/CD8)). Mitogen response studies showed low blastogenesis to PHA and PWM, with a mean c.p.m. +/- s.e.m. value of 1.7 +/- 0.67 x 10(4) for PHA (NL >/= 75 x 10(3)) and 8.42 +/- 4.1 x 10(3) for PWM (NL >/=25 x 10(3)). In conclusion, serum levels of inflammatory mediators were not predictive nor did they correlate with the severity of aGVHD. Recovery of NK cells, B cells, and PMN functions occurred within the first 90 days post transplant. However, T cell subsets, CD3+/CD4+ and CD3+/CD8+, and T cell functional activity remained significantly decreased and may account for the high incidence of infectious morbidity seen during this immediate post UCBT period.

Dysregulation of lymphokine production in the neonate and its impact on neonatal cell mediated immunity

Haematopoiesis and immune functions in cord blood (CB) are developmentally immature when compared with adult peripheral blood (APB). The defects in CB immune function and cytokine production may both contribute to the immaturity of CB immunity. We have studied the mechanisms associated with the dysregulation of myeloid lineage cytokines, GM-CSF and M-CSF, and lymphokines, IL-12, and IL-15 in activated CB when compared with APB MNC. Furthermore, we have studied the effects of IL-12 and IL-15 on induction of IFN-gamma and TNF-alpha production, NK, and LAK activities in CB and APB. GM-CSF, M-CSF, IL-12 and IL-15 protein and mRNA are decreased in activated CB MNC. These discrepancies are secondary, at least in part, to the altered post-transcriptional regulation. The impaired ability of CB to produce IL-12 and IL-15 in response to stimulation may contribute to the decrease in IFN-gamma, TNF-alpha production, NK and LAK activities. Furthermore, combination of low dose IL-12 and IL-15 may augment cytotoxic activities and minimize toxicity. These findings suggest that reduced cytokine expression from activated CB may contribute to the impaired CB cellular immunity and exogenous lymphokines may compensate for the immaturity in CB.

The regulation and biological activity of interleukin 12

Interleukin 12 (IL-12) is a pleiotropic cytokine and mediates several biological activities on human T and natural killer (NK) cells, including induction of IFN-gamma production, enhancement of cell-mediated cytotoxicity and comitogenic effects on resting T-cells. The major cellular sources producing IL-12 are antigen-stimulated monocytes, macrophages, and B-cells isolated from peripheral blood mononuclear cells (PBMC). Our laboratory has investigated the regulation of IL-12 gene expression in both cord blood and adult PBMC, and the effects of IL-12 on induction of IFN-gamma production, NK, and lymphokine-activated killer (LAK) cytotoxicity. IL-12 mRNA expression and protein production in LPS-stimulated cord blood MNC were 3-4 fold decreased when compared with adult PBMC. There were no differences between cord blood and adult PBMC in both basal levels of transcription or the degree of transcriptional activation of the IL-12 gene. Additionally, the half-life of IL-12 p40 mRNA was 3-fold lower in activated cord blood compared to adult PBMC. Exogenous IL-12 induced a significant increase of IFN-gamma from both cord and adult PBMC. Cord MNC has significantly reduced levels of NK activity, and IL-12 significantly enhanced cord blood NK cytotoxicity up to similar levels in adult PBMC. IL-12 also significantly enhanced cord blood NK and LAK activities against a broad range of neuroblastoma, leukemia, and lymphoma cell lines. Lower doses of IL-12 and IL-15 concomitantly generated either synergistic or additive effects on cord blood NK and LAK cytotoxicities. In light of the important biological functions of IL-12, reduced expression and production of IL-12 from activated cord blood may contribute to the immaturity of cord blood cellular immunity and contribute, in part, to decreased severe graft vs. host disease following unrelated cord blood stem cell transplantation. IL-12 enhancement of IFN-gamma, NK, and LAK activity in activated cord blood MNC up to comparable levels in adult PBMC suggests that exogenous IL-12 stimulation can compensate for the immaturity in cord blood cellular immunity. These characteristics of IL-12 biological activity strongly suggest its potential usefulness in future cancer immunotherapy.

Decreased interleukin-15 from activated cord versus adult peripheral blood mononuclear cells and the effect of interleukin-15 in upregulating antitumor immune activity and cytokine production in cord blood

Interleukin-15 (IL-15) is an important lymphokine regulating natural killer (NK) activity, T-cell proliferation, and T-cell cytotoxic activities. We hypothesized that the reduced expression and production of IL-15 from cord blood (CB) may contribute to the immaturity of CB immunity and potentially delay immune reconstitution after CB transplantation. We compared the expression and production of IL-15 from activated cord versus adult mononuclear cells (MNCs) and the regulatory mechanisms associated with IL-15 expression in CB MNCs. We have also studied the effect of exogenous IL-15 stimulation on CB and adult peripheral blood (APB) MNCs in terms of NK and lymphokine-activated killer (LAK) activities and cytokine induction. Lipopolysaccharide (LPS)-stimulated CB and APB MNCs were used to determine IL-15 expression and protein production by Northern analysis and Western immunoblot analysis. IL-15 mRNA expression and protein accumulation in CB MNC were 25% +/- 2.0% (12 hours, n = 4, P < .05) and 30% +/- 2.5% (12 hours, n = 3, P < .05), respectively, when compared with APB MNCs. Nuclear run-on assays showed no differences between CB and APB MNCs during basal levels of transcription and after transcriptional activation. However, the half-life of IL-15 mRNA was approximately twofold lower in activated CB MNCs than in activated APB MNCs (CB: 101 +/- 5.8 minutes v APB: 210 +/- 8.2 minutes, n = 3, P < .05). Exogenous IL-15 significantly enhanced CB NK and LAK activities up to comparable levels of APB (P < .05). IL-15 also significantly induced interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) protein production (days 1, 3, and 6, P < .05, n = 3) in CB MNCs. IL-15-stimulated LAK cells induced a significant lytic response against two acute lymphoblastic cell lines and two pediatric neuroblastoma cell lines. Both NK and LAK activities were augmented by the combination of IL-12 and IL-15, and the low-dose combination of IL-12 and IL-15 achieved similar levels of in vitro NK and LAK cytotoxicity compared with higher doses of either lymphokine. The present study suggests that IL-15 mRNA and protein expression is decreased in activated CB, secondary, in part, to altered posttranscriptional regulation. The reduced production of IL-15 from CB MNCs in response to stimulation may contribute to the decrease in IFN-gamma and TNF-alpha production and CB cellular immunity. However, exogenous IL-15 enhanced IFN-gamma and TNF-alpha production and NK and LAK cytotoxicities in CB MNCs. The reduced production of IL-15 from activated CB may contribute to the immaturity of CB cellular immunity and delayed immune reconstitution after unrelated CB transplantation. Exogenous IL-15 administration may compensate for the immaturity of CB immunity. The synergistic in vitro effects of low-dose IL-12 and IL-15 also implies the possible use of low doses each of IL-12 and IL-15 for enhancing immune reconstitution and/or possibly as a form of antitumor immunotherapy after CB transplantation.

Effects of phosphodiester and phosphorothioate antisense oligodeoxynucleotides on cell lines which overexpress c-myc: implications for the treatment of Burkitt's lymphoma

The product of the c-myc proto-oncogene is a highly conserved nuclear phosphoprotein whose expression is closely linked to cellular proliferation and differentiation. We have been interested in developing an antisense oligodeoxynucleotide (ODN) strategy to inhibit the proliferation of c-myc-dependent malignancies for use in future specific therapies and bone marrow purging regimens. Our experimental approach was to incubate either antisense or sense ODNs, spanning the 5' cap region of the c-myc gene, with c-myc overexpressing cell lines (HL-60) Raji, MJBL, CA-46) for up to seven days. Proliferation assay to test the inhibitory effect of an unmodified antisense ODN 15-mer (GCACAGCTCGGGGGT) showed that concentrations as low as 50 micrograms/ml significantly decreased proliferation of HL-60 cells by approximately 40% (P < 0.0001; n = 6) compared to controls. Clonogenic assays showed that the same antisense ODN inhibited colony formation by MJBL (40%0 and Raji (52%) cells. Subsequent experiments to study the effect of a more nuclease-stable, phosphorothioate-modified antisense ODN 18-mer (GCAGCACAGCTCGGGGGT) revealed 66% inhibition of HL-60 cell proliferation at 96 and 120 hours at 50 micrograms/ml, whereas sense ODN control had no effect. However, tenfold less of the modified antisense ODN (1 micrograms/ml) was required to inhibit proliferation of HL-60 cells by 50% compared to the unmodified antisense ODN. A decrease in the HL-60 native c-myc protein level was also observed with 100 micrograms/ml of modified antisense ODN, but not with the sense ODN control, by immunoblot analysis. Additionally, concentrations up to 10 micrograms/ml of either modified antisense or sense ODN did not decrease CFU-GM formation (145 +/- 35%, P = 0.27) in human bone marrow, suggesting that these levels of ODN would have a negligible effect on normal hematopoietic cells. These pilot data suggest that modified antisense ODN directed at the cap region of the c-myc gene could specifically inhibit c-myc expression at a single, lower dose than unmodified ODN and may play a future role in inhibiting the growth of c-myc-dependent malignant cells.

Cationic lipids reduce time and dose of c-myc antisense oligodeoxynucleotides required to specifically inhibit Burkitt's lymphoma cell growth

Burkitt's lymphoma is characterized by a translocation of the c-myc gene with one of the immunoglobulin loci which activates overexpression of the c-myc oncogene. Antisense-oligodeoxynucleotides (AS-ODNs) offer the potential to block specific c-myc gene expression within lymphoma cells, but often exhibit a low efficiency of AS-ODN uptake. In this study, a polycationic lipid reagent, Lipofectamine (LFM), was utilized as a vehicle to increase efficiency of delivery, decrease the time needed to observe an inhibitory effect, and decrease the AS-ODN dose. The objective was to develop a more efficient and rapid in vitro AS-ODN strategy to inhibit proliferation of c-myc-dependent lymphoma cells and to test the specificity of Burkitt's lymphoma cell line-directed AS-ODNs for potential use as molecular purging agents in bone marrow transplantation. Proliferation assays were performed to determine the inhibitory effect of the AS-ODNs on two Burkitt's lymphoma cell lines with different chromosomal translocations, Daudi and ST486, in medium containing 8.5 microM LFM. AS-ODNs at a concentration of 0.36 microM induced a significant decrease in proliferation for both cell lines using the specific AS-ODN for each respective translocation. Within 5 h, Daudi responded to its specific AS-ODN/lipid complexes with a 35% decrease in proliferation, compared to cells which received no treatment or Daudi-specific AS-ODN without LFM (P = 0.0001). Daudi showed an insignificant decrease in proliferation when treated with an AS-ODN specific for the ST486 translocation (4%, P = 0.26). ST486 proliferation was decreased by 52% when treated with the specific antisense for ST486 compared to no treatment or ST486-specific AS-ODN without LFM (P < 0.003). Treatment with the AS-ODN specific for Daudi showed an insignificant 4% decrease (P = 0.42). Controls, including sense ODN for structure, reverse AS-ODN for structure and base composition, and AS-ODN without LFM, did not produce a significant change in cells treated with LFM alone or cells receiving no treatment. Clonogenic assays of both Daudi and ST486 treated with their specific AS-ODNs revealed a 50% inhibition of colony formation after the 5 h incubation as compared to no treatment. Confocal laser scanning microscopy verified that cellular uptake of AS-ODN was enhanced by cationic lipids. Immunoblot analysis showed a 63 +/- 5% and a 50 +/- 3% reduction in intracellular c-myc levels for Daudi and ST486, respectively, when their respective AS-ODNs were administered. Normal bone marrow progenitors were unaffected by the ODN/LFM complexes. These results suggest that the specific c-myc AS-ODN/LFM complexes inhibit c-myc-dependent tumor proliferation at an earlier time and at a lower dose compared to no lipid facilitation. This approach may form the basis for utilizing specific AS-ODN/LFM therapy either alone or in a cocktail of other agents as an ex vivo molecular purging approach to autologous stem cell transplantation in Burkitt's lymphoma.

Differential mechanisms in the regulation of endogenous levels of thrombopoietin and interleukin-11 during thrombocytopenia: insight into the regulation of platelet production

The regulation of megakaryocytopoiesis and thrombopoiesis appears to be under the control of an array of hematopoietic growth factors. To determine the relationship of endogenous thrombopoietic cytokine levels and circulating platelet (PLT) counts, we measured the levels of thrombo-poietin (TPO), interleukin-11 (IL-11), and interleukin-6 (IL-6) in patients with significant thrombocytopenia secondary to both marrow hypoplasia and increased PLT destruction. Increased endogenous levels of TPO and IL-11, but not IL-6, were detected in bone marrow transplant patients with thrombocytopenia following myeloablative therapy (BMT/MAT) (TPO: 1,455.5 +/- 87.3 pg/mL, [PLT 39,600 +/- 7,800/microL], P < .001, n = 12; IL-11: 227.9 +/- 35 pg/mL, [PLT 32,900 +/- 57,000/microL], P < .05, n = 19; IL-6: 25.8 +/- 8.4 pg/mL, [PLT 32,800 +/- 5,057/microL], P > .05, n = 4] v normal donors [TPO < 150 pg/mL, n = 8; IL-11 < 50 pg/mL, n = 9; IL-6 < 10 pg/mL, n = 5 [PLT 203,000 +/- 7,500/microL]. There was a significant inverse correlation between endogenous levels of TPO and IL-11, but not IL-6, and PLT counts in the MAT/BMT patients (TPO: r = -0.57, P < .0001, n = 188; IL-11: r = -0.329, P < .0001, n = 249; IL-6: r = -0.1147, P > .05, n = 62). In patients with immune thrombocytopenia purpura (ITP), with decreased PLT survival, but intact bone marrow megakaryocytopoiesis, endogenous IL-11 levels were significantly increased (328.0 +/- 92.6 pg/mL, [PLT: 20,900 +/- 3,000/microL], P < .05, n = 25). However, endogenous TPO levels remained undetectable (< 150 pg/mL, [PLT 30,500 +/- 5,500/microL], n = 15). These results suggest that there may be differential mechanisms regulating endogenous TPO, IL-11, and IL-6 levels during acute thrombocytopenia and suggest that the absolute number of circulating PLTs may not always be the sole regulator of endogenous TPO levels. Other mpl-expressing cells of the megakaryocyte lineage may contribute to the regulation of circulating TPO levels as well. Our results also suggest IL-11 levels may in part, be regulated by a negative feedback loop based on circulating PLT counts, but also may, in part, be regulated by a variety of inflammatory agonists. Both TPO and IL-11, therefore, appear to be active thrombopoietic cytokines regulating, in part, megakaryocytopoiesis during states of acute thrombocytopenia.

Decreased interleukin-12 (IL-12) from activated cord versus adult peripheral blood mononuclear cells and upregulation of interferon-gamma, natural killer, and lymphokine-activated killer activity by IL-12 in cord blood mononuclear cells

Interleukin-12 (IL-12) is a critical cytokine regulating natural killer (NK) and T-cell function. We hypothesized that the impaired ability of cord blood (CB) to produce normal adult levels of IL-12 in response to stimulation may contribute to the immaturity of CB immunity. Furthermore, exogenous IL-12 may compensate for the immaturity in CB cellular immunity and have the potential for immunotherapy post cord blood transplantation. We compared the expression and production of IL-12 from activated cord versus adult mononuclear cells (MNC), regulatory mechanisms associated with IL-12 expression in CB MNC, and the effects of IL-12 on induction of CB interferon (IFN)-gamma production, NK, and lymphokine-activated killer (LAK) cytotoxicity. Northern analysis and enzyme-linked immunosorbent assay were performed in lipopolysaccharide (LPS)-stimulated CB and adult peripheral blood (APB) MNC. IL-12 mRNA expression was induced within 6 hours with LPS (10 micrograms/ml) and reached peak levels at 12 hours in both CB and APB MNC. However, IL-12 mRNA expression and protein accumulation in CB MNC were 35.8% +/- 4.84% (12 hours, n = 11, P < .05), and 17.6% +/- 1.7% (24, 72, 96 hours, n = 9, P < .05) respectively, when compared with APB MNC. Nuclear run-on assays showed no differences between CB and APB MNC in both the basal levels of transcription and the degree of transcriptional activation. However, the half-life of IL-12 p40 mRNA was approximately threefold lower in activated CB MNC than in activated APB MNC (CB: 114 +/- 3.0 minutes v APB: 353 +/- 7.8 minutes, n = 3, P < .05). Exogenous IL-12 (10 U/mL) induced a significant increase of IFN-gamma from both CB and APB MNC (24 hours, 72 hours, P < .05, n = 3). The stimulated CB IFN-gamma level reached comparable levels produced by unstimulated APB. IL-12 treatment also significantly enhanced CB NK cytotoxicity against K562 and NB-100 cell lines to the comparable levels of APB (P < .05, n = 4). CB MNC was more responsive to IL-12 stimulation with respect to IFN-gamma production, NK, and LAK cytotoxicity when compared with APB. The present study suggests that IL-12 mRNA and protein expression is decreased in activated CB. This discrepancy in IL-12 production is secondary, at least in part, to the altered posttranscriptional regulation. The impaired, ability of CB MNC to produce IL-12 in response to stimulation may contribute to the decrease in IFN-gamma production and NK cytotoxicity. However, IL-12 enhanced IFN-gamma and NK activity in CB MNC up to the comparable levels of APB MNC. These findings suggest that reduced expression and production of IL-12 from activated CB may contribute to the immaturity in CB cellular immunity and contribute, in part, to decreased graft-versus-host disease following CB stem cell transplantation.

Molecular biology and cytogenetics of non-Hodgkin's lymphoma in children

Molecular analysis, combined with cytogenetic studies of proto-oncogenes and tumor suppressor genes, has provided insight into the pathogenesis of non-Hodgkin's lymphoma. Characterization of these malignancies at the molecular level will aid in developing more sensitive detection methods for earlier and more accurate diagnosis. Thus, genetic rearrangements provide highly specific molecular markers for monitoring malignant cells. Additionally, a more detailed understanding of the precise, molecular steps leading to malignant transformation will facilitate the development of more specific and, perhaps, less toxic therapies.

Decreased macrophage colony-stimulating factor mRNA expression from activated cord versus adult mononuclear cells: altered posttranscriptional stability

We have previously shown that protein production and mRNA expression of granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF), and interleukin-3 are decreased in stimulated mononuclear cells (MNCs) from human umbilical cord compared with adult peripheral blood. These deficiencies may contribute to the increased susceptibility of neonates to infection. Macrophage colony-stimulating factor (M-CSF) regulates the proliferation, differentiation, and functional activation of monocytes. In the present study, we compared the regulation of M-CSF gene expression and protein production from stimulated cord and adult MNCs. Upon adhesion to tissue culture flasks, both cord and adult MNCs constitutively expressed M-CSF mRNA. In response to both adhesion and recombinant human GM-CSF (rhGM-CSF) stimulation for 120 hours, radioimmunoassays and bioassays showed that cord MNCs produced twofold to threefold less M-CSF protein compared with adult MNCs. Northern blot analysis also showed a fourfold decrease in M-CSF mRNA expression in both unstimulated and GM-CSF-induced cord versus adult MNCs. M-CSF mRNA expression in both cord and adult MNCs peaked between 16 and 24 hours and decreased to normal levels by 48 hours. We next determined the relative rates of transcription of the M-CSF gene by nuclear run-on assays in both cord and adult MNCs. The basal level signal of the M-CSF gene was similar between cord and adult MNCs. The transcriptional rate after stimulation with rhGM-CSF appeared to increase to a similar extent in both cord and adult MNCs (130% +/- 10% v 150% +/- 15%, C v A, n = 3, mean +/- SD). The comparative stability of M-CSF mRNA from cord versus adult MNCs was next determined by actinomycin D decay studies. The half-life of M-CSF mRNA from stimulated adult MNCs was 70 +/- 7.0 minutes (n = 4) compared with 47 +/- 2.8 minutes (n = 3) from stimulated cord MNCs (mean +/- SD, P < .05). To further determine the involvement of labile protein factors in posttranscriptional regulation, cord and adult MNCs were incubated with cycloheximide (CHX; 10 micrograms/mL). There was a significant increase in the induction of M-CSF mRNA by CHX treatment in both cord and adult MNCs. The increase of M-CSF mRNA induction by CHX was 2.5 times higher in cord MNCs compared with that in adult MNCs. These results suggest that there are one or more labile proteins that regulate M-CSF transcript stability in both cord and adult MNCs.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of interleukin-11 protein and mRNA expression in neonatal and adult fibroblasts and endothelial cells

Interleukin-11 (IL-11), a newly-identified cytokine produced by stromal cells, elevates platelet counts in neonatal rats in vivo and synergizes in vitro with IL-3 in supporting murine megakaryocyte colony formation and stimulating hematopoietic stem cells. Megakaryocytopoiesis is also enhanced by other colony-stimulating factors (CSFs), including IL-3, IL-6, and Steel factor (SLF). Dysregulation of neonatal thrombopoiesis predisposes newborns to develop thrombocytopenia during sepsis, despite increased circulating pools of committed thrombopoietic progenitors in newborn cord blood compared with adult. We previously reported reduced expression of granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte-colony-stimulating factor (G-CSF), and IL-3 from stimulated cord mononuclear cells, but increased expression of SLF in human umbilical vein endothelial cells (HUVEC). Therefore, we hypothesized that IL-3, IL-6, and SLF might modulate megakaryocytopoiesis by inducing IL-11 expression, and newborns might express altered levels of IL-11 mRNA expression during activated conditions, contributing to the difference in circulating colony-forming unit-megakaryocyte (CFU-Meg) cord and adult blood. Phorbol myristate acetate (PMA) induced a twofold greater increase in IL-11 mRNA expression in neonatal fibroblasts (NFb) compared with adult fibroblasts (AFb), and a 3.6-fold greater increase in HUVEC than human adult aorta endothelial cells (HAEC) by Northern blot analysis. PMA also induced a threefold greater increase in IL-11 protein production in NFb than AFb. Physiologic agonists IL-1 alpha, transforming growth factor-beta 1 (TGF-beta 1), and TGF-beta 2 triggered upregulation of IL-11 mRNA expression in both NFb and AFb. However, IL-3, IL-6, PIXY321 (a GM-CSF-IL-3 fusion protein), and SLF failed to upregulate IL-11 mRNA expression from the basal level, while macrophage-colony stimulating factor (M-CSF) mRNA was significantly induced. These data suggest that the hematopoietic effect of IL-6, SLF, and IL-3 on megakaryocytopoiesis is probably not mediated by secondary IL-11 mRNA expression. Similarly, inflammatory agonists IL-1 beta, lipopolysaccharide (LPS), and tumor necrosis factor-alpha (TNF-alpha) alone did not upregulate IL-11 expression from the basal level in endothelial cells, whereas intracellular adhesion molecule-1 (ICAM-1) and endothelial leukocyte adhesion molecule-1 were strongly induced. Minimal basal IL-11 expression was detected by reverse transcriptase-polymerase chain reaction (RT-PCR) in NFb, AFb, HUVEC and HAEC. The quantitative RT-PCR assay also verified that IL-1 beta and TNF-alpha-stimulated HUVEC and HAEC, and IL-3- and IL-6-stimulated NFb and AFb only expressed minimal levels of IL-11 mRNA.(ABSTRACT TRUNCATED AT 400 WORDS)

A randomized, placebo-controlled trial of recombinant human granulocyte colony-stimulating factor administration in newborn infants with presumed sepsis: significant induction of peripheral and bone marrow neutrophilia

Host defenses in the human neonate are limited by immaturity in phagocytic immunity. Such limitations seem to predispose infected newborns to neutropenia from an exhaustion of the neutrophil reserve. Among the critical defects thus far identified in neonatal phagocytic immunity is a specific reduction in the capacity of mononuclear cells to express granulocyte colony-stimulating factor (G-CSF) after stimulation. However, the safety, pharmacokinetics, and biological efficacy of administration of recombinant human (rh)G-CSF to infected human newborns to compensate for this deficiency is unknown. Forty-two newborn infants (26 to 40 weeks of age) with presumed bacterial sepsis within the first 3 days of life were randomized to receive either placebo or varying doses of rhG-CSF (1.0, 5.0 or 10.0 micrograms/kg every 24 hours [36 patients] or 5.0 or 10.0 micrograms/kg every 12 hours [6 patients]) on days 1, 2, and 3. Complete blood counts with differential and platelet counts were obtained at hours 0, 2, 6, 24, 48, 72, and 96. Circulating G-CSF concentrations were determined at hours 0, 2, 6, 12, 14, 16, 18, 24, and 36. Tibial bone marrow aspirates were obtained after 72 hours for quantification of the bone marrow neutrophil storage pool (NSP), neutrophil proliferative pool, granulocyte progenitors, and pluripotent progenitors. Functional activation of neutrophils (C3bi expression) was determined 24 hours after rhG-CSF or placebo administration. Intravenous rhG-CSF was not associated with any recognized acute toxicity. RhG-CSF induced a significant increase in the blood neutrophil concentration 24 hours after the 5 and 10 micrograms/kg doses every 12 and 24 hours and it was sustained as long as 96 hours. A dose-dependent increase in the NSP was seen following rhG-CSF. Neutrophil C3bi expression was significantly increased at 24 hours after 10 micrograms/kg every 24-hour dose of rhG-CSF. The half-life of rhG-CSF was 4.4 +/- 0.4 hours. The rhG-CSF was well tolerated at all gestational ages treated. The rhG-CSF induced a significant increase in the peripheral blood and bone marrow absolute neutrophil concentration and in C3bi expression. Future clinical trials aimed at improving the outcome of overwhelming bacterial sepsis and neutropenia in newborn infants might include the use of rhG-CSF.

Transforming growth factor-beta 1, macrophage inflammatory protein-1 alpha, and interleukin-8 gene expression is lower in stimulated human neonatal compared with adult mononuclear cells

Hematopoiesis is developmentally immature in the newborn compared with the adult. Diminished gene expression of several positive hematopoietic regulators has been observed in activated cord compared with adult peripheral blood mononuclear cells (MNC; Cairo et al. Pediatr Res, 30:362, 1991 and Cairo et al, Pediatr Res, 31:574, 1992). However, altered expression of negative hematopoietic regulators during states of increased demand may also contribute to the pathogenesis of newborn dyshematopoiesis. To test this hypothesis, we measured protein levels of transforming growth factor-beta 1 (TGF-beta 1) and macrophage inflammatory protein-1 alpha (MIP-1 alpha) in the conditioned media of human umbilical cord and adult MNC using specific enzyme-linked immunosorbent assays. There was significantly less TGF-beta 1 in culture supernatants of cord versus adult MNC after 24, 72, and 120 hours of stimulation (P < .05), and significantly less MIP-1 alpha in cord versus adult supernatants after 72 hours and 120 hours of stimulation (P < .01). We then examined the mRNA expression of the negative regulators TGF-beta 1, MIP-1 alpha, and interleukin-8 (IL-8) in cord and adult MNC using Northern blot hybridization followed by quantitative densitometry. Cord MNC expressed significantly less TGF-beta 1 mRNA than adult MNC 6 hours and 72 hours after stimulation (P < .001). Cord MNC expressed significantly less MIP-1 alpha mRNA than adult MNC 6 hours (P < .01), 24 hours (P < .001), and 72 hours after stimulation (P < .001). Cord MNC also expressed significantly less IL-8 mRNA than adult MNC 6 hours after stimulation (P < .001). Therefore, decreased mRNA accumulation appears to coincide with reduced cytokine expression in the activated cord MNC. There were no significant differences in the transcription rates determined by nuclear run-on assay of either the TGF-beta 1 or MIP-1 alpha gene in cord versus adult MNC after 6 hours of stimulation, suggesting that the reduced TGF-beta 1 and MIP-1 alpha mRNA in activated cord MNC may be secondary to alteration in posttranscriptional regulation. The present results, together with those of our previous studies, suggest that the altered expression of both positive and negative hematopoietic regulators may be involved in the immaturity of host defense in human neonates.

Circulating steel factor (SLF) and G-CSF levels in preterm and term newborn and adult peripheral blood

PURPOSE

An immaturity in humoral, cellular, and phagocytic immunity predisposes the newborn to overwhelming bacterial infection. The maturation and proliferation of early hemapoietic stem cells give rise to all three of these aspects of immunity. Defects in the regulation of early hematopoiesis may account in part for the immaturity of neonatal host defense. A new hematopoietic growth factor, Steel factor (SLF), has recently been demonstrated to induce the proliferation of early hematopoietic progenitor cells. Our purpose was to study SLF and its effect on hematopoiesis.

PATIENTS AND METHODS

We measured circulating serum SLF levels in preterm and term newborns and compared them to adults, matched third trimester pregnant mothers, and to circulating granulocyte colony-stimulating factor (G-CSF) levels.

RESULTS

There was no significant difference in SLF levels between preterm and term newborns and adults (3000 +/- 200 vs. 2700 +/- 200 vs. 3100 +/- 300 pg/ml) (Pt vs. T vs. A) (p = NS). Also, there was no significant difference between matched third trimester maternal levels and their matched term newborn (2650 +/- 330 pg/ml vs. 3530 +/- 400 pg/ml) (p = NS). However, G-CSF levels were significantly higher in preterm newborns compared to term newborns and adults (p < or = 0.025). The preterm newborn G-CSF levels, however, were significantly lower compared to positive controls obtained from neutropenic patients post bone marrow transplantation (ANC < or = 200/mm3) (174 +/- 86 vs. 669 +/- 82.3 pg/ml) (p < 0.001). Additionally, there were no significant differences in G-CSF levels between matched third trimester maternal samples and matched term newborns.

CONCLUSION

These studies suggest that circulating levels of SLF in the preterm and term newborn are similar to adults and do not account for differences in hematopoiesis.

Decreased endogenous circulating Steel factor (SLF) levels following allogeneic and autologous BMT: lack of an inverse correlation with post-BMT myeloid engraftment

We have previously demonstrated an inverse relationship between circulating endogenous G-CSF levels and myeloid engraftment post-BMT. A new early-acting hematopoietic growth factor, Steel factor (SLF), has recently been demonstrated to induce the proliferation of early hematopoietic progenitor cells and synergistically stimulate committed progenitor cells in the presence of lineage-specific CSFs. In this pilot study, we determined the temporal relationship between endogenous SLF levels and the circulating absolute neutrophil count (ANC) (myeloid engraftment) in both children and adults undergoing both allogeneic and autologous BMT. Pre-BMT SLF levels were 2600 +/- 100 pg/ml compared to significantly lower levels of G-CSF (30-50 pg/ml). The circulating SLF level was significantly decreased throughout the post-BMT period (ANC < or = 200 x 10(6)/l: 1500 +/- 600 pg/ml; ANC 200-500 x 10(6)/l: 1780 +/- 130 pg/ml; ANC > or = 500 x 10(6)/l: 1690 +/- 110 pg/ml) (p < 0.001). There was a lack of an inverse relationship between the circulating SLF level and the ANC (r = -0.43) (p = NS). For comparison, SLF levels from immune thrombocytopenia (platelet < = or 20 x 10(9)/l) and chemotherapy-induced neutropenia patients (ANC < or = 200 x 10(6)/l) were similar to pre-BMT levels but significantly higher than post-BMT levels (p < or = 0.02 and < or = 0.001, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased G-CSF and IL-3 production and gene expression from mononuclear cells of newborn infants

Newborns are predisposed to neutropenia and thrombocytopenia during bacterial sepsis. The presence of peripheral cytopenias during overwhelming infection may be secondary to decreased hematopoietic growth factor production during states of increased demand. We therefore examined circulating levels of granulocyte-colony stimulating factor (G-CSF) and IL-3, production of G-CSF and IL-3 from unstimulated and stimulated mononuclear cells (MNC), expression of G-CSF and IL-3 genes during unstimulated and stimulated conditions, and equilibrium and binding of G-CSF receptors on mature effector peripheral blood cells of adults and neonates. Serum from cord and adult peripheral blood contained negligible amounts of both G-CSF (less than or equal to 50 pg/mL) and IL-3 (less than or equal to 5 pg/mL). Constitutive supernatant levels of G-CSF and IL-3 from cord and adult unstimulated MNC were also undetectable. However, there was a significant difference in G-CSF and IL-3 production from stimulated cord and adult MNC. Supernatants from stimulated adult MNC had significantly more G-CSF (p less than 0.007) and IL-3 (p less than 0.02). Additionally, Northern blot hybridization and densitometry of autoradiographs demonstrated significantly more G-CSF and IL-3 mRNA transcripts from adult than from cord MNC. Lastly, affinity, binding, and number of G-CSF receptors on cord and adult peripheral effector cells were equal. These data suggest that, during states of increased demand, cord MNC produce less G-CSF and IL-3 than do adult MNC and have an associated reduction in their respective mRNA transcripts. These findings may have implications in the pathogenesis of neonatal cytopenias during states of increased demand, such as sepsis.

Circulating granulocyte colony-stimulating factor (G-CSF) levels after allogeneic and autologous bone marrow transplantation: endogenous G-CSF production correlates with myeloid engraftment

Myeloid engraftment after bone marrow transplantation (BMT) is influenced by a number of variables, including cytoreductive chemoradiotherapy, genetic disparity, number of reinfused committed myeloid progenitor cells, healthy microenvironment, and the presence of hematopoietic growth factors. Granulocyte colony-stimulating factor (G-CSF) stimulates proliferation of myeloid progenitor cells and enhances myeloid engraftment after BMT. We investigated the temporal relationship between endogenous G-CSF production and myeloid engraftment in both children and adults after allogeneic (ALLO) and autologous (AUTO) BMT. Circulating endogenous G-CSF levels ranged between 0 and 2552 pg/mL. The correlation coefficient between circulating serum G-CSF levels and the peripheral absolute neutrophil count (ANC) was r = -.875 (P less than .001). The endogenous serum G-CSF level was highest during the first week after BMT, when the ANC was less than or equal to 200/microL (699 +/- 82.3 pg/mL) (P less than .001). Both children and adults demonstrated a similar inverse relationship between circulating G-CSF level and degree of neutropenia. One patient failed to engraft after AUTO BMT and also failed to generate any endogenous G-CSF production. Lastly, once the serum G-CSF level decreased to less than 200 pg/mL, a mean of 6.1 +/- 0.9 days elapsed before the ANC was greater than or equal to 500/microL for 2 consecutive days. This study demonstrates that endogenous G-CSF production is associated with myeloid engraftment in both children and adults after AUTO and ALLO BMT and that the rate of increase and decrease in endogenous G-CSF may be predictive of either failure to engraft or duration of neutropenia.

Decreased stimulated GM-CSF production and GM-CSF gene expression but normal numbers of GM-CSF receptors in human term newborns compared with adults

We investigated cord and adult production of granulocyte-macrophage colony-stimulating factor (GM-CSF), expression of GM-CSF mRNA from unstimulated and activated mononuclear cells, and the affinity and presence of GM-CSF receptors on mature effector cells in an attempt to better understand the underlying pathophysiology of altered neonatal host defense. Utilizing 125I-GM-CSF as a ligand, Scatchard analysis revealed the presence of a single class affinity GM-CSF receptor with similar binding characteristics on both cord and adult peripheral PMN (kd = 44 and 39 pM) for adult and cord, respectively. Additionally, there was no significant difference in the number of GM-CSF receptors on cord versus adult neutrophils. Using a sandwich ELISA for measuring GM-CSF levels, we found nondetectable levels from supernatants of unstimulated cord and adult mononuclear cells and serum from cord and adult peripheral blood. However, there was a significant difference between cord and adult GM-CSF production from stimulated phytohemagglutinin and phorbol-12-myristate-6-acetate mononuclear cells (p less than 0.02). Additionally, GM-CSF mRNA expression from activated cord mononuclear cells was significantly reduced after 6 h of stimulation compared with adults. Nuclear run-on experiments revealed no difference in transcriptional activation from activated cord and adult mononuclear cells. Actinomycin D transcriptional decay studies, however, demonstrated reduced GM-CSF half-life from activated cord versus adult mononuclear cells (t1/2 30 versus 100 min). These results suggest normal affinity and numbers of GM-CSF receptors on peripheral mature effector cells but decreased GM-CSF production and GM-CSF mRNA expression from activated cord versus adult mononuclear cells.(ABSTRACT TRUNCATED AT 250 WORDS)

GM-CSF primes and modulates neonatal PMN motility: up-regulation of C3bi (Mo1) expression with alteration in PMN adherence and aggregation

Neonatal polymorphonuclear leukocytes (PMNs) are deficient in the expression of the adherence protein C3bi (Mo1), and are associated with reduced physiological inflammatory responses. We evaluated the priming and direct stimulating effect of recombinant human granulocyte-macrophage colony stimulating factor (rhGM-CSF) on newborn PMN expression of C3bi (Mo1), PMN adherence and PMN aggregation. Cord PMNs were incubated with rhGM-CSF (Amgen 4 x 10(7) U/mg) for 0-15 min, and C3bi surface receptor expression measured by immunofluorescence with CD11b, adherence with nylon wool, and aggregation using a Payton aggregometer. RhGM-CSF (15 min) significantly induced Mo1 expression: 250 pM/L 129.4 +/- 5.3% of C (p less than 0.001) 500 pM/L 141.5 +/- 4.1% (p less than 0.001), 1,000 pM/L 150.2 +/- 1.3% (p less than 0.0001). RhGM-CSF (1,000 pM/L x 5 min) followed by A23187 also primed newborn PMNs for increased Mo1 expression 122 +/- 4.5% of C (p less than 0.001). Additionally, rhGM-CSF (10 min) induced significant PMN adherence 50 pM/L 117.9 +/- 8.3% and 100 pM/L 131.5 +/- 5.7% of C (p less than 0.04). RhGM-CSF additionally primed newborn PMNs (100 pM/L) for increased adherence following A23187 (107.9 +/- 0.6% of C), p less than 0.02. Lastly, rhGM-CSF primed newborn PMNs for increased aggregation following FMLP: 100 pM/L, 15 min, 138.1 +/- 14.1%, p less than 0.0001. Co-incubating murine-antihuman GM-CSF AB 100 micrograms/ml neutralized 86.8 +/- 7.0% of newborn PMN Mo1 up-regulation. These studies demonstrate that rhGM-CSF primes and directly stimulates newborn PMNs for increased in vitro expression of Mo1, adherence, and aggregation.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of proton currents in neurones of the snail, Lymnaea stagnalis

1. Internal perfusion voltage-clamp and inside-out patch-clamp techniques were used to study the voltage-dependent H+ currents in snail neurone cell bodies. 2. In whole cells the voltage-activated outward H+ current was measured 60 ms after stepping to +40 mV with an internal pH (pHi) of 5.9 and no internal K+([K+]i = 0), and the delayed K+ current was measured 60 ms after stepping to +40 mV with pHi = 7.3 and [K+]i = 74 mM. The mean H+ and K+ current densities were 14.6 +/- 7.8 and 38.2 +/- 14.0 nA/nF, respectively, giving a mean ratio of the H+ to K+ current of 0.4 +/- 0.2. There is not a strong correlation between the densities of the two kinds of outward currents found in different cells. 3. Inside-out patch studies reveal that the H+ and K+ currents are distributed quite differently in the membrane. While 85% of all patches had K+ current, only five out of thirty-eight patches studied had H+ currents. In those five patches the H+ currents measured at +30 mV ranged from 10.7 to 21.0 pA, and the ratio of the H+ and K+ currents at +30 mV was 0.83 +/- 0.38. The mean H+ and K+ currents for all thirty-eight patches were 1.9 +/- 4.9 and 10.5 +/- 7.9 pA, respectively. 4. The current distribution patterns demonstrate that the H+ current does not flow through the delayed K+ current channels even though the two currents have similar voltage dependence and time course. 5. The relative ability of various extracellular divalent cations to block the H+ current was found to be Cu2+ approximately equal to Zn2+ greater than Ni2+ greater than Cd2+ greater than Co2+ greater than Mn2+ greater than Mg2+ = Ca2+ = Ba2+. Since 100 microM-Zn2+ blocks the H+ current more than it blocks the Ca2+ current, it can be used to reduce the contamination of Ca2+ current measurements by the H+ current. 6. The magnitude of the H+ current has a stronger temperature sensitivity than does the magnitude of the delayed K+ current. The Q10 of the H+ current magnitude is 2.1 +/- 0.4, while the Q10 of the K+ current magnitude is 1.4 +/- 0.04. This suggests a higher activation energy may be involved in the conduction of the H+ current than for K+ current. 7. The smooth time course of the H+ current measured in patches indicates that the size of the unitary H+ current is very small.(ABSTRACT TRUNCATED AT 400 WORDS)