The basis for the immunoregulatory role of macrophages and other accessory cells

Low serum conditions for in vitro generation of human macrophages with macrophage colony stimulating factor

Animal serum is often used to generate human macrophages in vitro. Since fetal calf serum (FCS) may complicate antigen uptake, processing and presentation on HLA molecules, we tested the ability of M-CSF to generate macrophages at low fetal calf serum conditions. Peripheral blood monocytes from 12 individuals were cultured 1-4 days with 0-100 ng/ml macrophage colony stimulating factor (M-CSF) at either 1 (low) or 5% (v/v) FCS. Regardless of number of days in culture, maximal (50-100 ng/ml) M-CSF stimulation and low FCS induced 65+/-5% esterase positive cells in all individuals compared to 52+/-7% without M-CSF (P<0.001). M-CSF increased the mean proportion of esterase positive cells after 24 or 96 h by 13% (P<0.005) and 13% (P<0.005), respectively, in 1% FCS, and 8% (P<0.05) and 2% (NS), respectively, in 5% FCS, indicating a slight negative interaction between 5% FCS and M-CSF (P<0.05). All cells were positive for CD14 and HLA class II, but cell number did not increase, confirming that M-CSF promote macrophage differentiation also at low FCS. M-CSF increased the average cell size after 24 or 96 h by 5.9+/-1.0 (P<0.05) and 8.6+/-0.5 (P<0.001) microm, respectively, without an increase in 5% FCS, further demonstrating the efficiency of M-CSF to promote macrophage generation at low FCS. The culture supernatants were negative for IL-1beta and TNF-alpha, which demonstrates that M-CSF did not activate the macrophages. The generation of human macrophages by M-CSF at low FCS should prove useful in studies where higher FCS concentrations may interfere with the assay.

Generation of high-titer retroviral vector-producing macrophages as vehicles for in vivo gene transfer

The goal of this project was to develop a novel gene transfer system based on macrophages (Mphi) as shuttles of recombinant retroviral vectors carrying therapeutic or marker genes. The murine Mphi cell line WGL5 was used as a source of Mphi for this study. We generated retrovirus-producing Mphi by transducing the WGL5 cells with a replication-defective retroviral vector carrying the enhanced green fluorescent protein (EGFP) reporter gene and the Moloney murine leukemia virus (MoMLV) as helper virus. We demonstrated stable integration of the recombinant retrovirus in the Mphi genome, efficient recombinant retrovirus production, and EGFP gene delivery to different cell lines in vitro. To evaluate Mphi-mediated EGFP gene transfer in vivo, allogeneic mice were injected s.c. with the retrovirus-producing WGL5 Mphi, that gave rise to solid tumor masses at the injection site, highly infiltrated with host leukocytes. We observed EGFP fluorescence in tumor-infiltrating CD4(+) and CD8(+) host T lymphocytes, providing direct evidence of the ability of engineered Mphi to mediate EGFP gene delivery to host cells in vivo. Moreover, we showed that retrovirus-producing Mphi could home to different organs in vivo following i.v. injection into mice. These data demonstrate that Mphi can be engineered as cellular vehicles for recombinant retroviruses carrying heterologous genes and suggest potential applications of this novel vector system for gene therapy.

Adrenocorticotropic hormone activates an outward current in cultured mouse peritoneal macrophages

To define the effects of adrenocorticotropic hormone (ACTH) in immunocompetent cells, ion channel activities in cultured mouse peritoneal macrophages were analyzed by the perforated patch-clamp method. ACTH induced outward currents at smaller holding potentials than K+ equilibrium potentials. Reversal potentials of ACTH-induced currents were dependent on external K+ concentrations, but not on external Cl- concentration. Quinine potently blocked the outward current and tetraethylammonium (TEA) partially suppressed that current. ACTH did not induce the response in Ca2+ free solution containing EGTA. These results suggest that ACTH can modulate macrophage functions through the activation of Ca2+ dependent K+ channels.

Human monocyte/macrophages activate by exposure to LPS overexpress NGF and NGF receptors

Monocyte/macrophages (M/M) represent the main cellular component of the immune system involved in the inflammatory response. In the present study we investigate whether NGF is produced by M/M and is involved in this event. The results show that unstimulated human M/M produce NGF and its synthesis is stimulated by LPS. The increase of NGF is associated with enhanced expression of high affinity NGF receptor on M/M and with no changes of low affinity NGF receptors (p75). The neutralization of endogenous NGF by NGF antibody in LPS-activated M/M, leads to overexpression of p75 receptor causing apoptosis. These findings provide new insight in the mechanisms governing monocyte survival in the inflamed tissue, representing a crucial aspect of host defence and maintenance of homeostasis.

Myeloma-reactive allospecific cytotoxic T lymphocytes lyse target cells via the granule exocytosis pathway

Accumulating evidence indicates that a graft-vs.-myeloma effect (GVM) and its associated clinical remission of the disease can be induced by donor lymphocyte infusion in myeloma patients who have relapsed after allogeneic bone marrow transplantation. Although it is believed that GVM is induced by allospecific T cells, T-cell subsets and the mechanisms involved in the killing of myeloma cells by donor T cells have not been studied. In this study, we generated allospecific cytotoxic T lymphocyte (CTL) lines against three different myeloma cell lines, ARK, ARP-1 and U266, from unmatched healthy donors and examined their cytotoxicity against the target cells. Our results demonstrate that the allospecific CTLs efficiently lysed myeloma cells. The observed cytotoxicity was mediated mainly by CD8+ T cells and inhibited by MHC class I-blocking antibody. Furthermore, the CTLs lysed the target cells via the perforin-mediated pathway, as concanamycin A, but not brefeldin A (the selective inhibitors for perforin- or Fas-mediated pathways respectively) or tumour necrosis factor-alpha (TNF-alpha)-blocking antibody, abrogated the cytolytic activity of the cells. These CTLs expressed and produced predominantly TNF-alpha and interferon-gamma (IFN-gamma), indicating that they belong to the type 1 T-cell subsets. Taken together, these results indicate that CD8+ allospecific T cells may be responsible for mediating GVM and that the granule-mediated lysis of target cells is the major pathway in the CD8+ T-cell response against myeloma cells.

The potent adjuvant activity of archaeosomes correlates to the recruitment and activation of macrophages and dendritic cells in vivo

The unique glycerolipids of Archaea can be formulated into vesicles (archaeosomes) with potent adjuvant activity. We studied the effect of archaeosomes on APCs to elucidate the mechanism(s) of adjuvant action. Exposure of J774A.1 macrophages to archaeosomes in vitro resulted in up-regulation of B7.1, B7.2, and MHC class II molecules to an extent comparable to that achieved with LPS. Similarly, incubation of bone marrow-derived DCs with archaeosomes resulted in enhanced expression of MHC class II and B7.2 molecules. In contrast, conventional liposomes made from ester phospholipids failed to modulate the expression of these activation markers. APCs treated with archaeosomes exhibited increased TNF production and functional ability to stimulate allogenic T cell proliferation. More interestingly, archaeosomes enhanced APC recruitment and activation in vivo. Intraperitoneal injection of archaeosomes into mice led to recruitment of Mac1alpha(+), F4/80(+) and CD11c(+) cells. The expression of MHC class II on the surface of peritoneal cells was also enhanced. Furthermore, peritoneal cells from archaeosome-injected mice strongly enhanced allo-T cell proliferation and cytokine production. The ability of archaeosome-treated APCs to stimulate T cells was restricted to Mac1alpha(high), B220(-) cells in the peritoneum. These Mac1alpha(high) cells in the presence of GM-CSF gave rise to both F4/80(+) (macrophage) and CD11c(+) (dendritic) populations. Overall, the activation of APCs correlated to the ability of archaeosomes to induce strong humoral, T helper, and CTL responses to entrapped Ag. Thus, the recruitment and activation of professional APCs by archaeosomes constitutes an efficient self-adjuvanting process for induction of Ag-specific responses to encapsulated Ags.

Avian T helper one/two immune response balance can be shifted toward inflammation by antigen delivery to scavenger receptors

Whether immune responses are dominated by inflammation or antibody production is often key to surviving infections. Therefore, differential control of these immune pathways determined by CD4 T cells is of fundamental interest for vaccine design. Little is known about how inflammatory [T helper cell (Th) type 1 (Th1)] versus antibody-inducing (Th2) choices are controlled in domestic fowl. To address this, MHC-matched chickens were immunized to test whether antibody-dominated Th2 or inflammatory Th1 responses could be preferentially activated, and our findings subsequently extended to outbred broiler breeders. Strategies used were known to shift the response in mice from Th2 to Th1 by delivering the injected antigen preferentially to macrophages. The model antigen, BSA, was maleylated to allow binding to scavenger receptors (SR) present on mammalian macrophages. Maleyl-BSA bound well in receptor-specific fashion to a chicken macrophage cell line. Compared with native BSA, immunization with SR-binding, maleyl-BSA modulated the immune response toward the Th1 pathway, as evident by increases in the magnitude of in vivo inflammatory reactions and declines in antibody-making responses. Initiation of a maleyl-BSA Th1 pathway is further supported by the enhanced ability of splenocytes to express mRNA for interferon-gamma in response to antigens. Together, these data establish the presence and functional relevance of SR in domestic fowl as well as provide a system for investigating the mechanisms controlling Th1/Th2 pathways in chickens. Moreover, the ability to direct immune responses toward either pathway by antigen maleylation will contribute significantly to the development of better vaccines for poultry diseases.

Nitric oxide inhibits INFgamma-induced increases in CIITA mRNA abundance and activation of CIITA dependent genes--class II MHC, Ii and H-2M. Class II TransActivator

BACKGROUND

Nitric oxide (NO) has been recently implicated as a powerful inhibitor of immune responses during allograft rejection, and some autoimmune and infectious diseases. We previously showed that one potential regulatory effect of NO is inhibition of IFNgamma-stimulated expression of Class II MHC on macrophages. Activation of this gene is mediated by the "Class II TransActivator" (CIITA). We now ask whether NO inhibits CIITA and thus the family of genes regulated by CIITA--Class II MHC, Ii, and H-2M. The latter two genes participate in antigen processing and formation of the cell-surface peptide-Class II MHC complex.

METHODS

Murine macrophages--both peritoneal macrophages and the RAW264.7 macrophage line--were stimulated in vitro with IFNgamma. NO production was measured by the Greiss reagent. Transcription of Class II MHC was measured by nuclear run-on assay. mRNA abundance of Class II MHC, Ii, H-2M, and CIITA was measured by Northern blotting and RT-PCR.

RESULTS

NO inhibits IFNgamma-induced increases in the abundance and transcription of the Class II MHC Ab gene. The increases in mRNA abundance of CIITA, Ii, and H-2M are also inhibited. As a control, we found that NO did not inhibit LPS-induce increases in TNFalpha mRNA abundance.

CONCLUSIONS

NO inhibits IFNgamma-induced increases in CIITA, and thus inhibits the CIITA-regulated genes: Class II MHC, Ii, and H-2M. Early during rejection, NO production by macrophages may result after stimulation by IFNgamma produced by CD4+ T cells, and be an effector of allograft damage. High concentrations of NO may then act as a feedback inhibitor which decreases antigen presentation by macrophages and thus decreases CD4 T cell activation.

Dose and time dependent effects of caffeine on superoxide release, cell survival and DNA fragmentation of alveolar macrophages from rat lung

In this study, the effect of two concentration ranges of the cAMP phosphodiesterase inhibitor, caffeine, on alveolar macrophage function was investigated by measuring survival rate, superoxide anion production and DNA fragmentation. The results show caffeine induced apoptosis in alveolar macrophages in a dose dependent manner. The survival rate of the cells exposed to low concentrations of caffeine (<5 mM) increased remarkably with a peak at 2.5 mM. At this concentration, caffeine failed to affect superoxide anion production and DNA degradation. However, at higher concentrations (5-20 mM), at which the viability was higher than the control, a significant increase in both superoxide production and DNA degradation, as judged by agarose gel and diphenylamine reaction, was obtained for 3 and 24 h of culture. The effect of caffeine on survival rate was also time dependent. At low caffeine concentrations, macrophages survived with a viability of 90-97% after 3 days. At moderate concentrations, the cells maintained viability up to 24 h but at concentrations higher than 20 mM, caffeine inhibited cell survival and killed a fraction of the population. The results suggest that low concentrations of caffeine prevent apoptosis of macrophages, whereas at moderate concentrations caffeine induces apoptosis in these cells. The results are discussed in relation to the mechanism of cAMP.

Enhancement of the immune response to hepatitis B virus vaccine by antigen specific IgM

In the present study, modulation of antibody response induced by Hepatitis B virus vaccine-IgM complex was investigated. Purified IgM-type anti HBv monoclonal antibody (1B11) was complexed to commercially available HBv vaccine (GenHevac B Pasteur, France) at varying concentrations of HBsAg (0.5, 1, 1.5 microg of HBsAg) and used to immunize BALB/c mice. An enhanced humoral immune response was obtained with the HBv vaccine-IgM complex at all the doses compared with those immunized by vaccine alone and increased antibody levels were observed with increased concentrations of HBsAg in vaccine formulation. Immunization with HBv vaccine-IgM complex mostly generated IgG-type antibodies in the sera of mice, and also gave rise to the development of hybrid cells which predominantly produced IgG-type monoclonal antibodies. Hence, results from this study indicate that 1B11 can be effectively used to obtain a better immune response to HBv vaccine.

Liposome-mediated cytosolic delivery of macromolecules and its possible use in vaccine development

In the majority of bacterial and viral infections the generation of cytotoxic T cells is of particular interest because such pathogens are able to escape the host defence mechanisms by surviving intracellularly within the phagocytic cells. To generate a CD8+ T lymphocyte response against exogenous antigens, the prerequisite is their delivery into the cytosol followed by processing and presentation along with class I major histocompatibility complex (MHC-I) molecules. In the present study we describe the method of liposome-based delivery of antigens and other macromolecules into the cytosol of target cells. To develop safe and effective methods for generating CD8+ T lymphocytes, we exploited the fusogenic character of lipids derived from lower organisms, that is baker's yeast (Saccharomyces cerevisiae). The degree of fusion with model membrane systems using yeast lipid liposomes varied from 40-70%, as opposed to 1-8% observed with egg PtdCho liposomes, depending on the assay system used. The fusion of yeast lipid liposomes with macrophages resulted in effective delivery of the entrapped solutes into the cytoplasmic compartment. This was further supported by the inhibition of cellular protein synthesis in J774 A1 cells by ricin A, encapsulated in the yeast lipid liposomes. Interestingly, the model antigen ovalbumin, when entrapped in the yeast lipid liposomes, successfully elicited antigen reactive CD8+ T cell responses. It may be concluded that the liposomes made of lipids derived from S. cerevisiae can spontaneously fuse with macrophages, delivering a significant portion of their contents into the cytoplasmic compartment of the cells.

Human asymptomatic Ebola infection and strong inflammatory response

BACKGROUND

Ebola virus is one of the most virulent pathogens, killing a very high proportion of patients within 5-7 days. Two outbreaks of fulminating haemorrhagic fever occurred in northern Gabon in 1996, with a 70% case-fatality rate. During both outbreaks we identified some individuals in direct contact with sick patients who never developed symptoms. We aimed to determine whether these individuals were indeed infected with Ebola virus, and how they maintained asymptomatic status.

METHODS

Blood was collected from 24 close contacts of symptomatic patients. These asymptomatic individuals were sampled 2, 3, or 4 times during a 1-month period after the first exposure to symptomatic patients. Serum samples were analysed for the presence of Ebola antigens, virus-specific IgM and IgG (by ELISA and western blot), and different cytokines and chemokines. RNA was extracted from peripheral blood mononuclear cells, and reverse transcriptase-PCR assays were done to amplify RNA of Ebola virus. PCR products were then sequenced.

FINDINGS

11 of 24 asymptomatic individuals developed both IgM and IgG responses to Ebola antigens, indicating viral infection. Western-blot analysis showed that IgG responses were directed to nucleoprotein and viral protein of 40 kDa. The glycoprotein and viral protein of 24 kDa genes showed no nucleotide differences between symptomatic and asymptomatic individuals. Asymptomatic individuals had a strong inflammatory response characterised by high circulating concentrations of cytokines and chemokines.

INTERPRETATION

This study showed that asymptomatic, replicative Ebola infection can and does occur in human beings. The lack of genetic differences between symptomatic and asymptomatic individuals suggest that asymptomatic Ebola infection did not result from viral mutations. Elucidation of the factors related to the genesis of the strong inflammatory response occurring early during the infectious process in these asymptomatic individuals could increase our understanding of the disease.

Chemokines and chemokine receptors in the pathogenesis of multiple sclerosis

In recent years we have seen growing evidence for the role of chemokines in the pathogenesis of several infectious and non-infectious inflammatory CNS disease states, including Multiple Sclerosis (MS) and its animal model, experimental allergic encephalomyelitis (EAE). An increase in proinflammatory chemokines has been associated with demyelinating lesions and clinical neurological dysfunction in patients with MS; these chemokines could be potential targets for MS therapy. Besides a clearly defined role in mediating leukocyte migration, these and other chemokines may act as immunoregulatory molecules in the driving to Th1/Th2 responses, switch of cytokine profiles, and the induction of tolerance. Since chemokine receptors have now been identified on macrophages, microglia, astrocytes, and endothelial cells as well as neurons in the CNS, chemokine/receptor interactions may mediate functional responses in a variety of CNS cell types during the course of inflammatory disease states. Therefore, clarification of the roles of chemokines and their receptors in the pathogenesis of EAE and MS will be useful in establishing immunotherapeutic strategies for these neurological autoimmune disorders.

Ascorbic acid modulates in vitro the function of macrophages from mice with endotoxic shock

The toxic effects of oxygen radicals produced by immune cells can be controlled to certain degree by endogenous antioxidants because of their scavenger action. This control is specially important in a type of immune cell, i.e., the phagocyte, which produces oxygen-free radicals and uses antioxidants in order to support its functions. Antioxidants, such as ascorbic acid (AA), are free radical scavengers and improve the immune response. In the pathogenesis of endotoxic shock, a disease with high mortality caused by gram-negative bacterial endotoxin, the reactive oxygen species (ROS) produced by phagocytes have been implicated. In a previous study, we observed in peritoneal macrophages from BALB/c mice suffering lethal endotoxic shock caused by intraperitoneal (i.p.) injection of Escherichia coli lipopolysaccharide (LPS; 100 mg/kg) a high production of superoxide anion. Therefore, in the present work, we have studied the in vitro effect of AA, at different concentrations (0.001, 0.01, 0.1, 1 and 2.5 mM), on the various steps of the phagocytic process, i.e., adherence to substrate, chemotaxis, ingestion of particles and superoxide anion production of murine peritoneal macrophages obtained from BALB/c mice with that of endotoxic shock, at 2, 4, 12 and 24 h after LPS injection. The increased adherence, ingestion and superoxide anion production by macrophages from animals with endotoxic shock were lower in the presence of AA, reaching similar values to those of the control animals. The most effective AA concentration in cells from mice with endotoxic shock was 0.01 mM. These data suggest that AA can regulate the phagocytic process in endotoxic shock, principally decreasing free radical production and thus it could reduce endotoxic shock severity.

CD137 (ILA/4-1BB), expressed by primary human monocytes, induces monocyte activation and apoptosis of B lymphocytes

Human CD137 is a member of the tumor necrosis factor (TNF) receptor family and the homologue of murine 4-1BB. Recent studies have demonstrated that CD137 promotes accessory T cell activation, and regulates proliferation and survival of T lymphocytes. This study reports on the expression and function of CD137 in peripheral blood monocytes. While monocytes showed constitutive expression in 10 out of 18 healthy donors, CD137 was not expressed on resting T or B lymphocytes. Immobilized antibodies to CD137 markedly induced the production of IL-8 and TNF-alpha protein and mRNA, and led to inhibition of IL-10 expression by primary monocytes. Furthermore, cross-linking of CD137 on monocytes resulted in an increase of B lymphocyte apoptosis mediated by direct cell-cell contact of both cell populations. In conclusion, this study identified CD137 as a new receptor involved in monocyte activation by inducing a characteristic cytokine release profile. In addition, CD137 may play a role in monocyte-dependent control of B lymphocyte survival.

LPS upregulates MHC class II I-A expression in B lymphocytes at transcriptional and at translational levels

Major histocompatibility complex (MHC) class II molecules are expressed in a limited number of cell types, including B lymphocytes, dendritic cells and macrophages. Lipopolysaccharide (LPS) increases the surface expression of class II molecules in a murine B-cell line by inducing an increase in I-A protein and I-A mRNA levels. LPS does not modify the rate of mRNA degradation; therefore, the increase in mRNA is due to an increase in transcription. In addition, LPS increases the levels of I-Aalpha protein, which correlates with an increase in ribosome loading for I-Aalpha but not for I-Abeta mRNA after treatment with LPS. Interestingly, in non-induced cells, I-Aalpha messenger RNA shows a significant peak of free mRNA. Therefore, LPS regulates the expression of MHC class II molecules at translational level in B cells, in addition to the transcriptional control. The actual mechanism implies changes of translation initiation rates, as shown by an increase ribosome loading in polysome gradients.

Stimulation of mouse macrophage antigen presentation by cocaine

Cocaine has been demonstrated to have multiple effects on the immune system. Here, we determined the effects of cocaine on macrophage antigen presentation, using an in vitro antigen presentation assay after macrophages were treated with cocaine both in vitro and in vivo. Our results showed that in vitro treatment of macrophages with cocaine significantly enhanced macrophage's ability to present ovalbumin (OVA) and the enhancement was also demonstrated in the macrophages of cocaine-injected mice. The presentation of an OVA-derived antigenic peptide (OVA323-339), however, was not affected. In vitro cocaine treatment neither affected antigen uptake nor major histocompatibility complex (MHC) II expression and the expression of co-stimulatory molecules B7. These results suggest that cocaine may act on an early event in the antigen handling by accessory cells.

Contribution of inflammatory cytokine release to activation of resident peritoneal macrophages after in vivo low-dose gamma-irradiation

The activation mechanism of resident peritoneal macrophages by in vivo gamma-irradiation was investigated. The function of macrophages as accessory cells in concanavalin A-induced proliferation of spleno-lymphocytes (accessory function) was enhanced 4 h after a low-dose irradiation (4 cGy) in vivo, but not in vitro, indicating that low-dose irradiation acts indirectly on the activation of macrophages. Because we expected that macrophages were activated by the recognition of substances damaged by in vivo irradiation, we co-cultured macrophages with oxidized erythrocyte-ghosts. No change was found in their accessory function. The production of inflammatory cytokines, interleukin-1 beta (IL-1 beta) and interferon-gamma (IFN-gamma), in the supernatant of cocultures of spleno-lymphocytes and macrophages was determined by an ELISA. Production of both increased in the presence of in vivo irradiated macrophages. Furthermore, IL-1 beta production from in vivo-irradiated macrophages treated with recombinant IFN-gamma also was enhanced. The mRNA expression of the cytokines released from macrophages and lymphocytes was determined by RT-PCR. Increases in IL-1 beta mRNA expression were found in both in vivo- and in vitro-irradiated macrophages. In vivo irradiation also enhanced the expression of IFN-gamma mRNA in lymphocytes, whereas there was no change after in vitro irradiation. On the basis of these observations, we propose that the activation of macrophages is caused by interaction with neighboring cells, such as lymphocytes, and by paracrine induction of certain cytokines which is initiated by the small amount of IL-1 beta released by irradiated macrophages.

Macrophage Colony-Stimulating Factor Induces the Expression of Mitogen-Activated Protein Kinase Phosphatase-1 Through a Protein Kinase C-Dependent Pathway

M-CSF triggers the activation of extracellular signal-regulated protein kinases (ERK)-1/2. We show that inhibition of this pathway leads to the arrest of bone marrow macrophages at the G0/G1 phase of the cell cycle without inducing apoptosis. M-CSF induces the transient expression of mitogen-activated protein kinase phosphatase-1 (MKP-1), which correlates with the inactivation of ERK-1/2. Because the time course of ERK activation must be finely controlled to induce cell proliferation, we studied the mechanisms involved in the induction of MKP-1 by M-CSF. Activation of ERK-1/2 is not required for this event. Therefore, M-CSF activates ERK-1/2 and induces MKP-1 expression through different pathways. The use of two protein kinase C (PKC) inhibitors (GF109203X and calphostin C) revealed that M-CSF induces MKP-1 expression through a PKC-dependent pathway. We analyzed the expression of different PKC isoforms in bone marrow macrophages, and we only detected PKCβI, PKCε, and PKCζ. PKCζ is not inhibited by GF109203X/calphostin C. Of the other two isoforms, PKCε is the best candidate to mediate MKP-1 induction. Prolonged exposure to PMA slightly inhibits MKP-1 expression in response to M-CSF. In bone marrow macrophages, this treatment leads to a complete depletion of PKCβI, but only a partial down-regulation of PKCε. Moreover, no translocation of PKCβI or PKCζ from the cytosol to particulate fractions was detected in response to M-CSF, whereas PKCε was constitutively present at the membrane and underwent significant activation in M-CSF-stimulated macrophages. In conclusion, we remark the role of PKC, probably isoform ε, in the negative control of ERK-1/2 through the induction of their specific phosphatase.

Distribution of immune cells in the epididymis of the aging Brown Norway rat is segment-specific and related to the luminal content

Remarkable changes occur during aging in the testis and epididymis of the Brown Norway rat. A dramatic increase in the number of halo cells, which are present in the epididymal epithelium and originate from the immune system, is found in animals of increasing age. Halo cells have been postulated to be either lymphocytes or monocytes. We hypothesized that halo cells are a mixture of different immune cells and that their relative composition changes with age. To verify this hypothesis, markers for helper T lymphocytes, cytotoxic T lymphocytes, B lymphocytes, and monocytes-macrophages were used to identify the major categories of immune cells in the epididymides of Brown Norway rats ranging in age from 3 to 24 mo. The numbers of immunocompetent cells in the epididymis were determined in relation to age, epididymal segment, and luminal content. We found that monocytes, helper T lymphocytes, and cytotoxic T lymphocytes belong to the population of halo cells. In addition, a segment-specific increase with age in the number of these immune cells was noted. Finally, we report a segment-specific recruitment of cytotoxic T lymphocytes and monocytes-macrophages in the epididymal epithelium of aged rats whose epididymal lumen contained few spermatozoa. We postulate that accumulation of damaged epithelial cells and antigens of germ cell origin, leaking through a dysfunctional blood-epididymis barrier, may contribute to the active recruitment of immune cells with age.

Conditional gene targeting in macrophages and granulocytes using LysMcre mice

Conditional mutagenesis in mice has recently been made possible through the combination of gene targeting techniques and site-directed mutagenesis, using the bacteriophage P1-derived Cre/loxP recombination system. The versatility of this approach depends on the availability of mouse mutants in which the recombinase Cre is expressed in the appropriate cell lineages or tissues. Here we report the generation of mice that express Cre in myeloid cells due to targeted insertion of the cre cDNA into their endogenous M lysozyme locus. In double mutant mice harboring both the LysMcre allele and one of two different loxP-flanked target genes tested, a deletion efficiency of 83-98% was determined in mature macrophages and near 100% in granulocytes. Partial deletion (16%) could be detected in CD11c+ splenic dendritic cells which are closely related to the monocyte/macrophage lineage. In contrast, no significant deletion was observed in tail DNA or purified T and B cells. Taken together, LysMcre mice allow for both specific and highly efficient Cre-mediated deletion of loxP-flanked target genes in myeloid cells.

Localization of macrophages in the chicken oviduct: effects of age and gonadal steroids

The aim of this study was to localize macrophages in the hen oviduct and determine the effects of age and gonadal steroids on their population. Cryostat sections of oviducal tissues from immature hens (60 d of age), virgin young (175 d of age), and old (620 d of age) laying hens, and immature hens (84 d of age) treated with gonadal steroids were immunostained for macrophages. The population of macrophages was analyzed by an image analysis system under a light microscope. Macrophages were observed in the stroma and mucosal epithelium of all oviducal segments of immature and laying hens. The population of macrophages in the oviducal stroma increased with age. Young laying hens had a significantly higher population of macrophages than immature hens in the vagina. Old laying hens had a significantly higher population than immature hens in the infundibulum, magnum, and vagina, and than young laying hens in the magnum. In the immature hens treated with gonadal steroids, the macrophage population increased only in the stroma of shell gland of the progesterone-treated birds. These results indicate that macrophage population in the oviducal stroma increases in association with sexual maturation and aging. Their population in the stroma may be partially affected by progesterone.

Are atopic individuals genetically predisposed to produce a specific protease profile in antigen processing?

Genetic factors play a major role in the development of allergic diseases such as asthma and atopic dermatitis. Since allergic response involves immune processes such as antigen-processing and -presentation, it is conceivable that the genes involved in the regulation of these processes may be crucial in determining an individual's susceptibility to allergic diseases. In this paper, it is proposed that proteases, used in antigen-processing, are involved in the genetic predisposition to allergic diseases.

Models to study the pathogenesis of thyroid autoimmunity

In vitro and in vivo models to study the pathogenesis of thyroid autoimmunity are reviewed. Animal models with experimentally induced or spontaneously developed autoimmune thyroid disease as well as transplantation models have been used extensively in these studies, but also the use of thyroid cell cultures from both humans and animals has contributed to the present state of knowledge. Cytokines may play a role in the pathogenic mechanism in thyroid autoimmunity. The major in vitro and in vivo effects of for example interleukin-1, tumour necrosis factor and gamma-interferon on differentiated thyroid cell functions are inhibitory. The advantage of using cell cultures has been the possibility of studying an influence on thyrocytes from a single agent individually, such as cytokines, hormones or growth factors. The disadvantage is that an organism is under the influence of a multitude of factors that can only be investigated in vivo in intact organisms. Both types of models have therefore been important in the understanding of thyroid autoimmunity.

Nitric oxide-mediated immunosuppression following murine Echinococcus multilocularis infection

In some parasitic infections immunosuppression is a prominent characteristic of the host-parasite interplay. We have used a murine alveolar echinococcosis (AE) model in susceptible C57BL/6 mice to document a suppressed splenocyte proliferative response to concanavalin A (Con A) at the early (1-month) stage and to Echinococcus multilocularis-crude antigen (Emc-antigen) at the late (4-6-month) stage of chronic infection. Despite proliferative suppression, splenic cytokine production [interleukin-2 (IL-2), IL-4 and interferon-gamma (IFN-gamma)] in response to Con A or Emc-antigen stimulation was not suppressed at 1 month postinfection (p.i.). Infection resulted in a strong Mac-1+ cell infiltration of the peritoneal cavity and spleen. Peritoneal cells (PEC) from mice infected at the 1-month stage were rich in macrophages and expressed significantly higher levels of transcripts for the inflammatory cytokine IL-1beta and for tumour necrosis factor-alpha and inducible nitric oxide synthase (iNOS), when compared with PEC from non-infected control mice. Conversely, the IL-10 transcript level remained low and did not change during infection. Spleen cells supplemented with PEC from infected mice induced a marked increase in the levels of nitrite in response to Con A and Emc-antigen stimulation, and also a complete suppression of splenic proliferation. The spleen cells from late-stage infected mice expressed only background levels of IL-10 but greatly increased levels of iNOS, when compared with normal spleen cells. This observation correlated with the immunosuppression demonstrated at the late stage of murine AE. Furthermore, the suppressed splenic proliferative responses observed at the early and late stage were reversed to a large extent by the addition of NG-monomethyl-l-arginine and partially by anti-IFN-gamma. Thus, our results demonstrated that the immunosuppression observed in chronic AE was not primarily dependent on IL-10 but rather on nitric oxide production by macrophages from infected animals.

Comparative effects of two endodontic irrigants, chlorhexidine digluconate and sodium hypochlorite, on macrophage adhesion to plastic surfaces

This study was designed to compare the "in vitro" effect of chlorhexidine digluconate, proposed as a new irrigant solution, with sodium hypochlorite, the currently irrigant solution used to disinfect the root canal system before obturation of the canal, on substrate adherence capacity of macrophages. Inflammatory macrophages were obtained from Wistar rats and resuspended in RPMI-1640 medium. The adherence capacity of macrophages to a plastic surface was determined. Assays were conducted in Eppendorf tubes for 15 min of incubation at 37 degrees C in an humidified atmosphere of 5% CO2 in air. The adherence index was calculated. Chlorhexidine digluconate inhibited substrate adherence capacity of macrophages in all conditions tested. Half-maximal inhibition (IC50) was observed at 1:5.6 dilution. Chlorhexidine digluconate was less potent than 5.25% sodium hypochlorite (IC50 = 1:24.1 dilution) in inhibiting substrate adherence capacity of macrophages. Taking into account that substrate adherence is the first step in the phagocytic process of macrophages and in antigen presentation, chlorhexidine digluconate could inhibit macrophage function and modulate inflammatory reactions at the level of inflamed periapical tissues.

The role of macrophages in T cell-mediated autoimmune diabetes in nonobese diabetic mice

We have shown previously that the inactivation of macrophages in nonobese diabetic (NOD) mice results in the prevention of diabetes; however, the mechanisms involved remain unknown. In this study, we found that T cells in a macrophage-depleted environment lost their ability to differentiate into beta cell-cytotoxic T cells, resulting in the prevention of autoimmune diabetes, but these T cells regained their beta cell-cytotoxic potential when returned to a macrophage-containing environment. To learn why T cells in a macrophage-depleted environment lose their ability to kill beta cells, we examined the islet antigen-specific immune response and T cell activation in macrophage-depleted NOD mice. There was a shift in the immune balance, a decrease in the T helper cell type 1 (Th1) immune response, and an increase in the Th2 immune response, due to the reduced expression of the macrophage-derived cytokine IL-12. As well, there was a deficit in T cell activation, evidenced by significant decreases in the expression of Fas ligand and perforin. The administration of IL-12 substantially reversed the prevention of diabetes in NOD mice conferred by macrophage depletion. We conclude that macrophages play an essential role in the development and activation of beta cell-cytotoxic T cells that cause beta cell destruction, resulting in autoimmune diabetes in NOD mice.

Modulation of murine macrophage function by N-acetylcysteine in a model of endotoxic shock

In previous studies we have observed changes in several functions of peritoneal macrophages from BALB/c mice with irreversible endotoxic shock caused by intraperitoneal injection of E. coli lipopolysaccharide (LPS) (100 mg/kg), which were associated with a high production of superoxide anion. Since antioxidants, such as N-acetylcysteine (NAC), are free radical scavengers that improve the immune response, in the present work we have studied different functions of peritoneal macrophages from BALB/c mice suffering the endotoxic shock above indicated and administered N-acetylcysteine (150 mg/kg i.p.) at 30 minutes after LPS injection. In the peritoneal macrophages obtained at 2, 4, 12 and 24 h after LPS injection, the following functions were studied: adherence to substrate, mobility, ingestion of particles, and production of superoxide anion and tumour necrosis factor (TNF alpha). The increase in adherence, ingestion and superoxide anion and TNF alpha production shown by macrophages from animals with endotoxic shock was counteracted by NAC injection. Moreover, the survival time of mice with endotoxic shock was increased in the presence of NAC. These data suggest that NAC, administered intraperitoneally, may be useful for the treatment of irreversible endotoxic shock by modulation of the function of macrophages with decreased superoxide anion and TNF alpha production and concomitant increase of survival time.

Heat shock and 5-azacytidine inhibit nitric oxide synthesis and tumor necrosis factor-alpha secretion in activated macrophages

To elucidate the role of stress response during macrophage activation, the effects of heat shock and the amino acid analog, 5-azacytidine on nitric oxide (NO) production, tumor necrosis factor-alpha (TNF-alpha) secretion, and heat shock protein (HSP) synthesis have been studied in murine peritoneal macrophages (C57BL/6). Heat shock (1 hr at 43 degrees C) or 5-azacytidine markedly inhibited the release of NO into the medium from interferon-gamma (IFN-gamma) plus lipopolysaccharide (LPS)-stimulated macrophages. Although heat shock significantly decreased TNF-alpha secretion only at the initiation stage of macrophage stimulation, 5-azacytidine treatment resulted in a more prolonged reduction in the secretion of TNF-alpha. When heat-shocked cells were stimulated with IFN-gamma plus LPS under normal culture conditions at 37 degrees C, the heat shock-induced inhibition of NO release reversed progressively with increasing recovery time. Although the total amount of cellular HSP72 measured by Western blot increased time-dependently over 7 hr, newly synthesized HSP72 measured by [35S]methionine incorporation was evident only after 1 and 3 hr of recovery time after heat shock treatment. At these time points, the lowest nitrite accumulation and TNF-alpha secretion into the medium was evident. It is concluded that signaling pathways related to newly synthesized HSP such as HSP72 are implicated in the down regulation of NO synthesis and TNF-alpha secretion in macrophages.

Time dependent production of cytokines and eicosanoids by human monocytic leukaemia U937 cells; effects of glucocorticosteroids

In the present study the human monoblast cell line U937 has been used as a model to study the function of human mononuclear phagocytes in asthma. The kinetics of the production of eicosanoids and cytokines, which are thought to play a role in the pathogenesis of asthma, were studied. In addition, the effects of glucocorticosteroids were investigated, as these drugs are of great importance for the treatment of asthmatic patients. After stimulation with phorbol-12 myristate acetate (PMA) for 24 h, U937 cells were cultured in the absence or presence of lipopolysaccharide (LPS: 1 and 5 microg ml(-1)) and glucocorticosteroids (budesonide, fluticasone propionate and prednisolone: 10(-11), 10(-9) and 10(-7) M) for 96 h. The production of interleukin-1beta (IL-1beta), interleukin-6 (IL-6), prostaglandin E2 (PGE2) and thromboxane B2 (TxB2) gradually increased in time after stimulation with LPS, whereas the transient production of tumor necrosis factor alpha (TNF-alpha) reached its maximum between 6 and 12 h. Interferon-gamma (IFN-gamma), interleukin-10 (IL-10) and leukotriene B4 (LTB4) were not detectable. All three glucocorticosteroids (budesonide, fluticasone propionate and prednisolone) completely inhibited the production of both eicosanoids and cytokines. The production of eicosanoids was more sensitive to these glucocorticoids than the production of cytokines. The observed differences in the kinetics of the production of eicosanoids and cytokines stress the importance of time course experiments in studies on the effect of drugs on mononuclear cells.

Enhanced expression of activation-associated molecules on macrophages of heterogeneous populations in expanding periapical lesions in rat molars

Exudative macrophages are the most prevalent inflammatory cells during the entire pathogenetic process in experimentally induced rat periapical lesions. To clarify the significance of macrophages in the pathogenesis of periapical lesions, the way in which the phenotype of ED1 (a general marker for mononuclear phagocytes)-positive cells is modulated in actively expanding lesions was investigated, by immunoperoxidase staining with a panel of antibodies that recognize several activation-associated molecules on macrophages. Periapical lesions were induced experimentally by exposing the pulp in the lower first molars of Wistar rats. Active lesion expansion with morphological diversification of ED1-positive cells occurred between 14 and 28 days after the injury. Double immunoperoxidase staining revealed that ED1-positive cells coexpressing class II molecules of the major histocompatibility complex (MHC) molecules, inducible nitric oxide synthase (iNOS) and/or CD11a increased during the period of active lesion expansion. Increases of endothelial cells expressing intracellular adhesion molecule-1 and CD25 (interleukin-2 receptor)-expressing lymphocytes were also seen during the same period. Moreover, there existed two particular subpopulations of ED1 + cells in the established lesion at 28 days: (1) ED1++/class II MHC - /iNOS+ cells, located around the periapical abscess, and (2) ED1+/class II MHC+/ iNOS- cells with slender or dendritic morphology, distributed predominantly in the outer portion of the lesion where T lymphocytes were abundant. The first cell type could be a macrophage with potent phagocytic and antimicrobial actions, and the second might possess sufficient antigen-presenting capacity to cause the activation of T lymphocytes. It was concluded that macrophages, when activated, may participate in triggering lesion expansion. Functionally distinct subpopulations of macrophages may occupy different sites within the lesion where they can most effectively exert their specific functions.

Effects of endotoxic shock in several functions of murine peritoneal macrophages

Gram negative sepsis and septic shock continue to be a major medical problem, with a complex physiopathology and it is associated with high mortality. Although secretion of cytokines such as tumor necrosis factor-alpha by macrophages is the principal host mediator of septic shock, other characteristic functions of macrophages implicated in their phagocytic capacity have not been studied in the process of endotoxic shock. In the present study we have used an intraperitoneal injection of E. coli lipopolysaccharide (LPS) (100 mg/kg) in order to obtain an endotoxic shock model in adult female BALB/c mice. Peritoneal cell suspensions were obtained at several times (2, 4, 12 or 24 h) after injection and the following functions were studied on the peritoneal macrophages: adherence to substrate, mobility (spontaneous and directed or chemotaxis), ingestion of particles and superoxide anion production. The results showed a stimulation of adherence, ingestion and superoxide production as well as a decrease of chemotaxis in the animals injected with LPS. These effects changed with time after LPS injection. Thus, the increase of adherence and the decrease of mobility were higher during the first hours, whereas the increase in ingestion and superoxide production turned larger with time.

Antigen presentation by cisplatin-activated macrophages: role of soluble factor(s) and second messengers

Cisplatin [cis-dichlorodiammine platinum (II)], a potent anti-tumour compound, stimulates immune responses by activating macrophages and other cells of the immune system. The mechanism by which cisplatin activates these cells is poorly characterized. Present investigations were undertaken to study the mechanism of antigen presentation by cisplatin-treated macrophages. Cisplatin-treated macrophages showed a biphasic pattern of antigen presentation to keyhole limpet haemocyanin (KLH)-primed T cells. The second phase of antigen presentation was not due to the continuous presence of cisplatin in the culture medium; rather, it was induced by soluble factors released by cisplatin-treated macrophages. Co-incubation of macrophages with cisplatin and inhibitor of serine/threonine or protein tyrosine phosphatase resulted in an augmentation of cisplatin-induced antigen presentation. In contrast, treatment of macrophages with cisplatin and inhibitor of protein kinase C or protein tyrosine kinase inhibited cisplatin-induced antigen presentation. These observations suggest that antigen presentation by cisplatin-treated macrophages is regulated by reversible action of protein phosphatases and kinases. The antigen-presenting ability of cisplatin-treated macrophages was also inhibited by EGTA, nifedipine, TMB-8, W-7 and calmidazolium, suggesting the probable involvement of Ca2+, calmodulin and calmodulin-dependent kinases in this process.

Clinical islet cell transplantation. Are we there yet?

Diabetes mellitus is perhaps the most devastating chronic disease of all time. A brief history of the evolution of treatment modalities is provided, culminating in the rationale for the physiologic replacement of a functioning beta-cell mass by transplantation. Vascularized pancreas transplantation is discussed briefly as an introduction to the transplantation of the isolated islet. A detailed review of the current state of human islet transplantation for the cure of diabetes is then described. Finally, areas for future development are highlighted.

Induction of outward current by orexin-B in mouse peritoneal macrophages

To define effects of novel feeding regulating peptides, orexins, in immunocompetent cells, ion channel activity in mouse peritoneal macrophages was analyzed by the perforated patch-clamp method. Orexin-B (OX-B) induced an outward current at smaller holding potentials than K+ equilibrium potentials. Reversal potentials of OX-B induced current were dependent on external K+ concentrations but not on external Cl- concentration. Orexin-A is less effective than OX-B. Quinine blocked the outward current and tetraethylammonium partially suppressed the current. These results suggest that OX-B can modulate macrophage functions through the activation of Ca2+-dependent K2+ channels.

Activation of human monocytes induces differential resistance to apoptosis with rapid down regulation of caspase-8/FLICE

Cells of the monocyte/macrophage lineage play a central role in both innate and acquired immunity of the host. However, the acquisition of functional competence and the ability to respond to a variety of activating or modulating signals require maturation and differentiation of circulating monocytes and entail alterations in both biochemical and phenotypic profiles of the cells. The process of activation also confers survival signals essential for the functional integrity of monocytes enabling the cells to remain viable in microenvironments of immune or inflammatory lesions that are rich in cytotoxic inflammatory mediators and reactive free-radical species. However, the molecular mechanisms of activation-induced survival signals in monocytes remain obscure. To define the mechanistic basis of activation-induced resistance to apoptosis in human monocytes at the molecular level, we evaluated the modulation of expression profiles of genes associated with the cellular apoptotic pathways upon activation and demonstrate the following: (i) activation results in selective resistance to apoptosis particularly to that induced by signaling via death receptors and DNA damage; (ii) concurrent with activation, the most apical protease in the death receptor pathway, caspase-8/FLICE is rapidly down-regulated at the mRNA level representing a novel regulatory mechanism; and (iii) activation of monocytes also leads to dramatic induction of the Bfl-1 gene, an anti apoptotic member of the Bcl-2 family. Our findings thus provide a potential mechanistic basis for the activation-induced resistance to apoptosis in human monocytes.

Immunohistochemical studies in equine recurrent uveitis (ERU)

Despite extensive clinical research, the etiology of equine recurrent uveitis (ERU) is still unknown. After an immunologic pathogenesis was established in recurrent uveitis in humans, a similar pathogenic mechanism was assumed to exist in ERU. To investigate whether immunopathologic mechanisms are involved in ERU, 20 eyes of 15 horses with ERU were examined immunohistochemically with a T cell marker, B cell marker, and anti-major histocompatibility complex (MHC) class II antibodies. Twenty-six eyes of 20 horses were used for investigation of MHC class II antigen expression in normal equine eyes. In 18 eyes of 14 horses, the number of T cells in the inflammatory cell population within the uvea was assessed. In 16/18 eyes (89%), the T lymphocyte fraction was > 70%. This cell population was distributed mostly in a diffuse manner throughout the uvea and also within the mantle zone of follicular lymphocytic aggregates. Foci of B lymphocytes could be found within the center of follicular aggregates in three eyes. The expression of MHC class II antigen on resident ocular cells was evaluated in 10 eyes of six horses with ERU. An increase of MHC class II antigen expression in the trabecular meshwork and on the nonpigmented ciliary epithelium was noted as was a deviant expression on proliferating Müller cells and retinal pigment epithelial cells. The predominance of T cells in the inflammatory infiltrates supports the central role of a cell-mediated immune response. Furthermore, the observation of a deviant MHC class II expression on resident ocular cells suggests that aberrant immune regulation may play a role in the pathogenesis of ERU.

Locoregional response and increased natural killer activity after intratumoral injection of HLA-B7/beta2-microglobulin gene in patients with cancer

The purpose of this study was to assess the therapeutic potential of injecting the gene for HLA-B7/beta2-microglobulin into the subcutaneous metastatic nodules of patients who are refractory to conventional treatments. The nine patients evaluated were divided into three groups and given escalating doses of DNA (20, 40, and 100 microg of the HLA-B7 plasmid DNA/lipid complex for each group) every 2 weeks. Biopsy specimens from the treated tumor nodules of all nine patients were positive for the presence of DNA and for HLA-B7 mRNA expression. Moreover, in six of the nine patients, immunohistology of tumor biopsy samples revealed the expression of recombinant HLA-B7 protein. Also, all nine patients showed an increase in NK activity in their circulating peripheral blood lymphocytes. In two lung cancer patients, one partial and one mixed response was observed after gene transfer. These responses were confined to the treated nodules and the untreated locoregional lymph nodes; the lung masses showed no regression. Remission durations were 14 and 6 weeks, respectively, and in a total of 35 cycles no significant toxicities were observed. Immunohistologic analysis revealed an increased infiltration of CD4+ T cells, macrophages, and NK cells after therapy. In two responding cases, direct intratumoral injection of an allogeneic class I gene could elicit an antitumor response in locoregional areas, possibly through the activation of NK cells.

Macrophages in the chicken oviduct: morphometrical studies by light and transmission electron microscopy and the possible influence of sex hormones

Light and electron microscopic techniques were used to study the morphometry and dynamic changes of macrophages in the postnatal and sex hormone-treated chicken oviduct, respectively. Abundant typical macrophages, containing clear vacuoles, well-developed mitochondria, Golgi complexes and lysosomal bodies in their cytoplasms, were observed in the lamina propria of all segments of the postnatal chicken oviduct, occurring more frequently in the vaginal part. When 7-day-old chickens were injected with diethylstilbestrol (DES), and DES plus progesterone, infiltration of a significant number of macrophages in both groups, but not in controls could be seen. The light and electron microscopic structures of the macrophages in both postnatal and sex hormone-treated chicken oviduct were similar. These results show that typical macrophages are present in the chicken oviduct; their frequency of occurrence varies with different oviductal segments, and they are influenced by sex hormones.

Responses of macrophage-associated antigen-expressing cells in the dental pulp of rat molars to experimental tooth replantation

Bacterial infection of the dental pulp is a major hindrance to successful pulp regeneration after tooth replantation. This study examined how macrophages and class II molecule-expressing cells of the pulp respond to tooth replantation, on the hypothesis that they contribute to the defence and repair of the traumatized pulp. Upper right first molars of 5-week-old male Wistar rats were replanted immediately after extraction; contralateral untreated teeth served as controls. Pulpal cells expressing macrophage-associated antigens were immunohistochemically demonstrated at 0 h (immediately after the replantation) to 84 days postoperatively using antirat monoclonal antibodies OX6 (anti-class II molecules), ED1 (pan-macrophage antibody, reactive also with dendritic cells) and ED2 (anti-resident macrophages). Between 3 and 7 days postoperatively, ED1+ and OX6+ cells, but not ED2+ cells, were concentrated in areas of degeneration formed in the coronal pulp, and frequently showed a marked accumulation along the pulp-dentine border of the cuspal area. Confocal laser scanning microscopy revealed that some of the OX6+ cells with a dendritic profile extended several cytoplasmic processes into the dentinal tubules communicating with the enamel-free area at the tip of the cusp. From 14-84 days, approx. two-thirds of specimens exhibited pulp-tissue regeneration with increasing formation of reparative dentine. Following the formation of sound reparative dentine, cells positive to each antibody were distributed more centrally in the pulp than in the controls, and thus did not show any accumulation along the pulp-dentine border. However, in the other specimens where a bone-like hard tissue had formed in the pulp chamber, many ED1+ and OX6+ cells were still concentrated in the remaining pulp tissue and showed a marked accumulation along the pulp dentine border. Few ED2+ cells were observed in these specimens. These findings suggest that, following tooth replantation, exudative macrophages are actively engaged in eliminating dentinal tubule-derived infectious stimuli and that class II molecule-expressing cells, most probably containing dendritic cells, are positioned strategically at the outermost portion of the injured pulp to monitor incoming antigens. The intensity of the pulpal defence reaction may be dependent on the status of hard-tissue formation, which influences the amount of incoming antigens.

Translational Control of MHC Class II I-A Molecules by IFN-γ

MHC class II molecules are expressed in a limited number of cell types, including B lymphocytes and macrophages (Mφ). IFN-γ increases the surface expression of class II molecules in a murine B cell line without inducing detectable changes in either I-A or I-A mRNA levels. In bone marrow-derived Mφ, IFN-γ causes an increase in class II expression at both the mRNA and surface levels. In addition to the increase in transcription rates described for Mφ, IFN-γ increases the rate of synthesis of IAα and IAβ proteins and the ribosome loading for both mRNA molecules in both cell types. Interestingly, there is a significant peak of free I-A mRNA in noninduced cells. Therefore, IFN-γ regulates the expression of MHC class II molecules at the translational level in both B cells and Mφ and, as already reported, at the transcriptional level only in Mφ. The actual mechanism of regulation causes changes in the translation initiation rates in both cell types, as demonstrated by an increase in ribosome loading in polysome gradients.

Distribution of macrophage lineage cells in rat gingival tissue after topical application of lipopolysaccharide: an immunohistochemical study using monoclonal antibodies: OX6, ED1 and ED2

To discuss the role of macrophage lineage cells on the periodontal tissue destruction, we immunohistochemically examined the phenotype and the dynamics of macrophage lineage cells 1 or 3 h or 1, 2, 3 or 7 d after topical application of LPS (5 mg/ml in physiological saline) from the rat gingival sulcus using 3 monoclonal antibodies: OX6 (antigen-presenting cells), ED1 (monocytes, macrophages and dendritic cells) and ED2 (resident macrophages). We could detect at least 3 different types of macrophage lineage cells, namely OX6+/ED1+/ED2- dendritic cells and exudate macrophages and ED2+ resident macrophages. After LPS application the majority of macrophage lineage cells accumulated in the subjunctional epithelial area were newly extravasated OX6+/ED1+/ED2- dendritic cells or macrophages. The number of these cells increased progressively with time and reached a maximum level at d 2. On the other hand, number and tissue distribution of ED2+ resident macrophages did not change. These results indicate that several types of macrophage lineage cells exist in rat gingival tissue and suggest that dendritic cells and exudate macrophages transiently accumulated after LPS application are responsible for various host immune response and tissue destruction caused by LPS.

Direct exposure to gallium arsenide upregulates costimulatory activity of murine macrophages

Gallium arsenide (GaAs) is an intermetallic semiconductor compound used in the electronics industry. Acute exposure of animals to GaAs systemically suppresses several immune functions while paradoxically causing inflammation at the exposure site. We investigated the effect of GaAs on costimulatory activity of murine peritoneal macrophages, 5 days after ip exposure. Costimulation by macrophages was determined by activation of CD4(+) helper T cell hybridomas to secrete interleukin-2 in the presence of immobilized monoclonal anti-CD3 antibody. Both peritoneal exudate cells (PEC) and resident peritoneal cells exposed to GaAs provided greater costimulation to the T cells than vehicle control cells. Resident peritoneal cells exposed to GaAs were also more efficient than latex bead-exposed cells, indicating that phagocytosis alone did not cause the GaAs effect. Double immunofluorescence staining and flow cytometric analysis revealed that GaAs-exposed PEC had increased cell surface expression of costimulatory B7-1 and B7-2 molecules and intracellular adhesion molecule-1 (ICAM-1) compared to controls. In addition to these molecules, resident peritoneal macrophages exposed to GaAs also expressed significantly higher levels of heat-stable antigen (HSA). Monoclonal antibodies specific for these costimulatory molecules significantly inhibited T cell activation, demonstrating that the molecules on GaAs-exposed cells were functional. In contrast, GaAs did not upregulate costimulatory molecules on splenic macrophages. These findings suggest that direct GaAs exposure improves macrophage costimulatory activity, possibly by activating the cells, which may contribute to respiratory inflammation caused by inhalation of GaAs particles.

Selective expansion and continuous culture of macrophages from adult pig blood

Macrophages were selectively expanded and continuously cultured from adult pig blood. One-half ml of heparinized adult pig blood was inoculated directly into the medium overlaying a feeder layer of STO mouse fibroblasts. After attachment to the feeder cells for 24 h, the culture was washed several times with the medium to remove most of any unattached blood cells and re-fed. Approximately 7 x 10(4) blood monocytes were initially detected and enumerated by specific binding of DiI-labeled acetylated low density lipoprotein (DiI-Ac-LDL). Macrophage outgrowths appeared in the primary culture after 6-7 days. The macrophages grew to relatively high density in 2-3 weeks (2-3 x 10(6) cells/T25 flask), and the culture was passaged on to fresh STO feeder layers to begin secondary culture. Over 2-3 months of culture the macrophage replication produced as many as 1.4 x 10(9) DiI-Ac-LDL-positive cells. The macrophages grew on top of the feeder cells in two forms: either a semi-attached, round morphology, or a closely adherent, flat ameboid morphology with several extended pseudopods. Electron microscopic examination revealed the cells to be uniformly of macrophage character and that 4-5% were giant cells. The macrophages were phagocytic and expressed CD14 on their surfaces. They also reacted positively with pig macrophage-specific monoclonal antibody (mAb), and were negative for reactivity with pig T- and B-cell-specific mAb. This simple method for isolating and propagating macrophages may indicate the replicative capacity of either adult pig blood monocytes or circulating blood stem cells, and it may be useful in providing macrophages for general research, virological assay, adoptive-immunotherapy models, and somatic gene therapy models.