Quantitative variation in la antigen expression plays a central role in immune regulation

Proteomic Signature Reveals Modulation of Human Macrophage Polarization and Functions Under Differing Environmental Oxygen Conditions

Macrophages are innate immune cells which can react to a large number of environmental stimuli thanks to a high degree of plasticity. These cells are involved in a variety of tissue functions in homeostasis, and they play essential roles in pathological contexts. Macrophages' activation state, which determines their functional orientation, is strongly influenced by the cellular environment. A large body of macrophage literature is devoted to better defining polarizations from a molecular viewpoint. It is now accepted that a multidimensional model of polarization is needed to grasp the broad phenotype repertoire controlled by environmental signals. The study presented here aimed, among other goals, to provide a molecular signature of various polarizations in human macrophages at the protein level to better define the different macrophage activation states. To study the proteome in human monocyte-derived macrophages as a function of their polarization state, we used a label-free quantification approach on in-gel fractionated and LysC/Trypsin digested proteins. In total, 5102 proteins were identified and quantified for all polarization states. New polarization-specific markers were identified and validated. Because oxygen tension is an important environmental parameter in tissues, we explored how environmental oxygen tension, at either atmospheric composition (18.6% O₂) or "tissue normoxia" (3% O₂), affected our classification of macrophage polarization. The comparative results revealed new polarization-specific makers which suggest that environmental oxygen levels should be taken into account when characterizing macrophage activation states. The proteomic screen revealed various polarization-specific proteins and oxygen sensors in human macrophages. One example is arachidonate 15-lipoxygenase (ALOX15), an IL4/IL13 polarization-specific protein, which was upregulated under low oxygen conditions and is associated with an increase in the rate of phagocytosis of apoptotic cells. These results illustrate the need to consider physicochemical parameters like oxygen level when studying macrophage polarization, so as to correctly assess their functions in tissue.

Contrasting effects of IFNα on MHC class II expression in professional vs. nonprofessional APCs: Role of CIITA type IV promoter

We previously demonstrated that, in ex vivo cultures, IFNα downregulates the expression of MHC class II (MHCII) genes in human non-professional APCs associated with pancreatic islets. IFNα has an opposing effect on MHCII expression in professional APCs. In this study, we found that the mechanism responsible for the IFNα-mediated MHCII's downregulation in human MHCII-positive non-professional antigen presenting human non-hematopoietic cell lines is the result of the negative feedback system that regulates cytokine signal transduction, which eventually inhibits promoters III and IV of CIITA gene. Because the CIITA-PIV isoform is mostly responsible for the constitutive expression of MHCII genes in non-professional APCs, we pursued and achieved the specific knockdown of CIITA-PIV mRNA in our in vitro system, obtaining a partial silencing of MHCII molecules similar to that obtained by IFNα. We believe that our results offer a new understanding of the potential significance of CIITA-PIV as a therapeutic target for interventional strategies that can manage autoimmune disease and allograft rejection with little interference on the function of professional APCs of the immune system.

Castration prevents suppression of MHC class II (Ia) expression on macrophages after trauma-hemorrhage

Several studies indicate that cell-mediated immune responses, i.e., macrophage (MΦ) cytokine release capacities, myosin heavy chain (MHC) class II (Ia) expression, etc., are suppressed after trauma-hemorrhage in male mice. Testosterone has been shown to be responsible for the depression of MΦ cytokine responses in males after trauma-hemorrhage. Antigen presentation via MHC class II plays a key role in initiating and maintaining cell-mediated and humoral immune responses. It remains unknown, however, whether testosterone has any effect on MHC class II after trauma-hemorrhage. To study this, male C3H/HeN mice were castrated or sham castrated 2 wk before trauma (midline laparotomy) and hemorrhage (Hem; blood pressure 35 ± 5 mmHg for 90 min and resuscitation) or sham operation. Four hours thereafter, MHC class II (Ia) expression was measured using flow cytometry. The results indicate that MHC class II (Ia) expression on peritoneal and splenic MΦ was significantly suppressed in male mice after trauma-hemorrhage. Prior castration, however, prevented the depression in MHC class II (Ia) expression on peritoneal and splenic MΦ after trauma-hemorrhage. Castration did not affect MHC class II (Ia) expression in MΦ from sham-castrated mice. Thus testosterone depresses MHC class II (Ia) expression on peritoneal and splenic MΦ after trauma-hemorrhage in males. Because MHC class II is necessary for an adequate immune response, our results suggest that depletion of male sex steroids or blockade of androgen receptors using agents such as flutamide might prevent immunosuppression via maintaining MHC class II (Ia) expression after trauma and severe blood loss.

Antigen-driven murine CD4+ T lymphocyte proliferation and interleukin-2 production are diminished by dietary (n-3) polyunsaturated fatty acids

This study is the first to describe the impact of consuming a diet rich in (n-3) polyunsaturated fatty acids (PUFA) from fish oil on antigen-driven activation of naive CD4+ T lymphocytes. To accomplish this, we used lymphocytes isolated from T cell receptor (TCR) transgenic mice (i.e., DO11.10). A large portion of the T lymphocytes from these mice expresses a TCR specific for a peptide within the ovalbumin (OVA) molecule (OVA(323-339)). When this antigen is presented in the context of major histocompatibility complex I-A(d) with costimulation, these naive CD4+ T cells become activated, produce interleukin (IL)-2 and clonally expand. (n-3) PUFA enrichment was accomplished by feeding DO11.10 mice one of two nutritionally complete experimental diets that differed only in the source of fat: lard or menhaden fish oil [high in (n-3) PUFA]. After 2 wk of consuming the experimental diets, lymphocytes were isolated from the spleen of each mouse, then cultured in the presence of antigen (i.e., OVA(323-339)) or concanavalin A (Con A), a nonspecific, polyclonal T cell stimulus. IL-2 production and lymphocyte proliferation were determined after 48 and 72 h, respectively. Naive CD4+ T lymphocytes from fish oil-fed mice stimulated with antigen produced less IL-2 ( approximately 33%; P < 0.001) and proliferated to a lesser extent ( approximately 50%; P < 0.0001) than the same cells from lard-fed DO11.10 mice. When stimulated with Con A, (n-3) PUFA did not affect either proliferation or IL-2 production. In summary, we report for the first time that feeding mice a diet enriched with (n-3) PUFA reduces in vitro antigen-stimulated production of IL-2 and subsequent proliferation of naive CD4+ T lymphocytes.

Polymorphism in the Y box controls level of cytokine-mediated expression of HLA-DRB1 genes

The HLA class II molecules play an important role in immune response. The quality of immune response is dependent not only on the polymorphisms in the class II molecules, but also on the level of their cell-surface expression. In fact, it has been demonstrated that differences in the level of expression of DRB1 and DRB3 genes restricted and activated distinct CD4+ T lymphocytes. We and others have previously described allelic polymorphisms in the upstream regulatory regions of DRB genes, which affected DNA-protein interactions and resulted in significantly different promoter strengths. We showed that polymorphisms in both the X1 and Y box motifs affect level of constitutive expression of DRB1 genes in the DR1, DR51 and DR53 haplotype groups. In the present study, we examined the effect polymorphisms in the X1 box and the Y box on the cytokine (interferon-gamma (IFNgamma), tumor necrosis factor-alpha (TNFalpha) and granulocyte macrophage-colony-stimulating factor (GM-CSF))-mediated transcriptional activities of DRB1 promoters in these, i.e. DR1, DR51 and DR53, haplotype groups. The results demonstrate that the polymorphism in the X1 box does not affect cytokine-mediated strength of DRB1 gene promoters. In contrast, the polymorphism in the Y box, which affects the inverted CCAAT sequence, plays a dominant role on the cytokine-mediated transcriptional activity of DRB1 promoters.

Dietary carotenoids and human immune function

The colorful group of compounds known as carotenoids are present in many plants, where they provide photoprotection and act as accessory pigments in photosynthesis. Many epidemiologic studies have shown strong associations between diets rich in carotenoids and a reduced incidence of many forms of cancer, and that finding led to the suggestion that the antioxidant properties of those compounds might help protect immune cells from oxidative damage, thus enhancing their ability to detect and eliminate tumor cells. Since the early 1980s, there have been reports supporting that hypothesis. However, more recently, after large prospective studies did not show protective effects of beta-carotene supplementation, more attention has been given to studies defining optimal levels of intake that can be achieved within a well-balanced diet. The latest intervention studies have suggested that, in well-nourished, healthy individuals, a moderate level of carotenoid supplementation is neither beneficial nor harmful. However, supplementation might be appropriate in undernourished or less healthy individuals, particularly if they are elderly. Future studies comparing supplements with real foodstuffs, combined with postgenomic technologies, will help define optimal intakes for different sectors of the population.

The role of the class II transactivator (CIITA) in MHC class I and II regulation and graft rejection in kidney

Class II transactivator (CIITA) induces transcription of MHC class II genes, and induces class I in some cell lines. We examined the effect of CIITA deficiency on class I and II expression in mouse kidney. In CIITA knockout (CIITAKO) mice, basal class II was absent, but class I levels were mildly but significantly increased. Allogeneic stimulation or ischemic injury increased class I and II expression in kidneys of control (wild-type, WT) mice but induced only class I in CIITAKO mice. Thus, in kidney, all basal and induced class II expression was CIITA-dependent, but neither basal nor induced class I was CIITA-dependent. Rejecting kidney allografts from CIITAKO mice in CBA hosts manifested intense induction of donor class I but no donor class II expression. Rejecting kidneys from both WT and CIITAKO donors showed predominantly CD8 T-cell infiltration at days 7 and 21, with increasing tubulitis and arteritis at day 21. CIITAKO kidneys showed fewer infiltrating cells than WT kidneys at day 21. Thus CIITA-deficient kidneys have no basal and induced class II expression but display intense induction of class I expression, and evoke typical rejection lesions, although some indices of infiltration are reduced at day 21.

Low-dose supplementation with lycopene or beta-carotene does not enhance cell-mediated immunity in healthy free-living elderly humans

OBJECTIVE

To assess the effects of supplementation with the carotenoids, beta-carotene or lycopene, at levels achievable within a diet rich in fruit and vegetables, on immune function in a group of free-living healthy elderly.

DESIGN

A double-blind randomized placebo-controlled trial. T cell subsets and the expression of functionally associated cell surface molecules, quantified by flow cytometry, and lectin-stimulated lymphocyte proliferation, were compared before and following the treatment period.

SUBJECTS

Fifty-eight subjects aged over 65 y were recruited; 52 were included in the final analysis.

INTERVENTIONS

Participants received one placebo, one lycopene (13.3 mg) or one beta-carotene (8.2 mg) capsule daily for 12 weeks.

RESULTS

No significant differences were observed in any of the parameters examined following either lycopene or beta-carotene supplementation.

CONCLUSIONS

In well-nourished, free-living, healthy elderly individuals, supplementation with relatively low levels of beta-carotene or lycopene is not associated with either a beneficial or detrimental effects on several aspects of cell-mediated immunity.

HLA-DRB1 gene transcripts in rheumatoid arthritis

Susceptibility to rheumatoid arthritis (RA) is associated with defined HLA-DRB1 alleles. However the molecular basis of this association is not known. Peculiarities in the expression of disease-linked DRB1 alleles could be involved since in healthy controls HLA-DRB1 gene expression varies according to the alleles in B cells. Peripheral blood B cells of healthy controls and RA patients were examined for their level of allelic DRB1 transcripts using a competitive PCR approach. Levels of DRB1 transcripts were greatly modified in RA and influenced by HLA-DRB1 genotype: patients with double dose of RA-associated alleles displayed up-regulated amounts of DRB1 gene transcripts whereas patients carrying either a single or no at risk allele had low levels of DRB1 transcripts, compared to control individuals. These differential levels of DRB1 gene expression were not influenced in any way by clinical, biological or therapeutic features of the patients. Various amounts of DRB1 mRNA may be related to variations of the density of DR molecules on B cells and consequently could influence the response of CD4 T cells. This particular regulation of DRB1 gene expression in RA patients could therefore represent one of the molecular mechanisms involved in the association of HLA DRB1 genes to RA.

Sequence analysis of the DRB1 promoter reveals limited polymorphism with no influence on gene expression

HLA-class II promoters contain a set of conserved regulatory regions necessary for constitutive and induced gene expression. For the HLA-DQB as well as for the DRB1 promoter sequence, polymorphisms with influence on gene expression have been reported. In contrast to these data we could show that there is very limited allele-specific polymorphism among the HLA-DRB1 promoter alleles. In a long range PCR we amplified a DNA sequence containing the promoter and the second exon of the DRB1 gene in one fragment. Nested PCR products of this PCR fragment for the promoter and for the second exon were analysed by DNA sequencing to allow the linkage of a promoter to its DR allele. Most investigated DRB1 alleles exhibited the same promoter consensus sequence except for two point mutations. An A to T transversion (position -70 bp) was closely associated with DRB1*08, whereas a C-deletion (position -30 bp) was most commonly observed together with DRB1*10. Both polymorphisms did not influence promoter activity in luciferase reporter gene assays.

Review: the role of omega 3 fatty acids in intestinal inflammation

The role of polyunsaturated fatty acids (PUFAs) in inflammatory lesions of the intestines is the subject of increasing research. This review begins with a background discussion of the source, elongation, and desaturation of PUFAs, as well as the role they have played in the human diet through evolution. The available data and hypotheses as to how manipulation of PUFAs might effect the various components of the immune system are then provided. Possible mechanisms by which PUFAs result in immunomodulation include alterations in eicosanoid synthesis, membrane fluidity, signal transduction, intraluminal bacteria, and gene expression. Attention is then turned to the known effects that these polyunsaturated fatty acids have on the various individual components of the immune system including lymphocytes, neutrophils, and antigen presenting cells, as well as the immunoregulatory process of apoptosis. Finally, laboratory data on the role of PUFAs in necrotizing enterocolitis, and to a greater extent inflammatory bowel disease, first as demonstrated in animal models of the disease, and second in human studies are then summarized.

Effects of lycopene and lutein supplementation on the expression of functionally associated surface molecules on blood monocytes from healthy male nonsmokers

It has been suggested that dietary carotenoids can enhance immune function. Supplementation with beta-carotene (15 mg daily) was previously shown to enhance human monocyte function. To examine the effect of other dietary carotenoids, two similar independent studies were done. Healthy adult male nonsmokers were randomly assigned to receive lycopene (study 1), lutein (study 2), or placebo for 26 days, followed by the alternative treatment for another 26 days. The expression of functionally related monocyte surface molecules was quantified by laser flow cytometry before and after each treatment period. There was a significant increase in plasma levels of each carotenoid following dietary supplementation, but the effects on monocyte surface molecule expression were not as striking as those observed after beta-carotene supplementation. These findings emphasize that it cannot be assumed that the effect of one carotenoid will be the same as another, even at the same level of intake.

Cyclosporin A reduces expression of adhesion molecules in the kidney of rats with chronic serum sickness

Treatment with cyclosporin A (CsA) improves proteinuria and reduces renal cellular infiltration in chronic serum sickness (CSS). We examined if these effects were associated with a reduced renal expression of CD54 and its ligands, interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha) and MHC class II molecules. We studied two groups of rats in which CSS was induced by daily injections of ovalbumin (OVA): a group treated with CsA (OVA.CsA group, n = 11) and a group that received no treatment (OVA.CSS group, n = 11). An additional group of five rats (control group) received only phosphate buffer. Immunostaining techniques were used to follow CSS and to study the expression of CD54, CD18, CD11b/c, IFN-gamma, TNF-alpha and MHC class molecules. Proteinuria (mg/24 h) was reduced from 248.2 +/- 73.1 (OVA.CCS group) to 14.5 +/- 13.1 with CsA treatment (P < 0.0001). The renal expression of CD54 and its ligands (CD18 and CD11b/c) was reduced by 50% to 75%. Correspondingly, there was a 60% to 85% reduction in the number of infiltrating leucocytes. The number of cells expressing TNF-alpha, IFN-gamma and MHC II molecules was also reduced. CsA reduces expression of CD54 and its ligands. This effect is associated with a reduction of cellular infiltration, IFN-gamma, TNF-alpha-producing cells and with MHC II expression in the kidney. These findings suggest that expression of adhesion molecules plays a critical role in CSS and underline the importance of cellular immunity in this experimental model.

Immature B lymphocytes from adult bone marrow exhibit a selective defect in induced hyperexpression of major histocompatibility complex class II and fail to show B7.2 induction

Mature B lymphocytes respond to antigen receptor ligation by phenotypic changes, including up-regulation of major histocompatibility complex class II molecules and expression of B7.2, which are required for initiating and sustaining a productive interaction with T helper cells. We have previously demonstrated that neonatal B cells fail to show a similar up-regulation of class II and B7.2 expression following B-cell receptor (BCR) ligation, although these responses could be induced by other stimuli. Here we demonstrate that immature B cells from adult bone marrow exhibit even more profound defects in these responses, as they fail to up-regulate class II in response to either BCR ligation or interleukin-4. Moreover, bone marrow-derived, immature B cells could not be induced to express B7.2 either by receptor cross-linking or by lipopolysaccharide. These differences in the inducible expression of class II and B7.2 appear to be intrinsic to the B cells, as they were retained in purified populations of B-lineage cells and could not be induced in mature B cells by co-culture with bone marrow cells. Furthermore, short-term culture of bone marrow permitted B-cell maturation, which was accompanied by acquisition of responsiveness to the same stimuli as mature, splenic B cells. The inability of immature B cells to show these responses provides a molecular explanation for their reported deficiency in interacting with T cells. Failure of immature B cells to inducibly express B7.2 may also be important for the establishment of self tolerance in the B-cell compartment.

n-3 polyunsaturated fatty acids inhibit the antigen-presenting function of human monocytes

Diets rich in n-3 polyunsaturated fatty acids (PUFAs) are associated with suppression of cell-mediated immune responses, but the mechanisms are unclear. We hypothesized that n-3 PUFAs can inhibit the function of human antigen-presenting cells. A prerequisite for this role of blood monocytes is the cell surface expression of major histocompatibility complex (MHC) class II molecules [human leukocyte antigen (HLA)-DR, -DP, and -DQ], aided by the presence of intercellular adhesion molecule-1 (ICAM-1) and leukocyte function associated antigens 1 and 3. We showed previously that the n-3 PUFA eicosapentaenoic acid (EPA) inhibits the expression of HLA-DR on unstimulated human monocytes in vitro, but that docosahexaenoic acid (DHA) enhances its expression. However, both n-3 PUFAs suppress the expression of HLA-DR, HLA-DP, and ICAM-1 on interferon-gamma-activated monocytes. We also established that dietary fish-oil supplementation can inhibit the expression of these surface molecules on circulating human monocytes. We subsequently showed that when EPA and DHA were combined in the same ratio as is commonly found in fish-oil-supplement capsules (3:2), there was no significant effect in vitro on the expression of HLA-DR on unstimulated monocytes, but the expression on activated monocytes remained significantly inhibited. In the same in vitro system, the ability of activated monocytes to present antigen to autologous lymphocytes was significantly reduced after culture with the combined n-3 PUFAs. These findings provide one potential mechanism for the beneficial effect of fish oil in the treatment of rheumatoid arthritis, a disorder associated with elevated expression of MHC class II and adhesion molecules on monocytes present within affected joints.

The B-cell system of human mucosae and exocrine glands

The mucosae and exocrine glands harbour the largest activated B-cell system of the body, amounting to some 80-90% of all immunoglobulin (Ig)-producing cells. The major product of these immunocytes is polymeric (p)IgA (mainly dimers) with associated J chain. Both pIgA and pentameric IgM contain a binding site for the polymeric Ig receptor (pIgR), or secretory component (SC), which is a requirement for their active external transport through secretory epithelia. The pIgR/SC binding site depends on covalent incorporation of the J chain into the quaternary structure of the polymers when they are produced by the local immunocytes. This important differentiation characteristic appears to be sufficient functional justification for the J chain to be expressed also by most B cells terminating at secretory effector sites with IgD or IgG production; they probably represent a "spin-off" from sequential downstream CH switching on its way to pIgA expression, thus apparently reflecting a maturational stage of effector B-cell clones compatible with homing to these sites. Observations in IgA-deficient individuals suggest that the magnitude of this homing is fairly well maintained even when the differentiation pathway to IgA is blocked. Certain microenvironmental elements such as specific cytokines and dendritic cells appear to be required for induction of IgA synthesis, but it remains virtually unknown why this isotype normally is such a dominating product of local immunocytes and why they have such a high level of J chain expression. Also, despite the recent identification of some important requirements in terms of adhesion molecules (e.g. integrin alpha 4 beta 7 and MAdCAM-1) that explain the "gut-seeking" properties of enterically induced B cells, the origin of regionalized homing of B cells to secretory effector sites outside the gut remains elusive. Moreover, little is known about immune regulation underlying the striking disparity of both the class (IgD, IgM) and subclass (IgA1, IgA2, IgG1, IgG2) production patterns shown by local immunocytes in various regions of the body, although the topical microbiota and other environmental stimuli might be important. Rational design of local vaccines will depend on better knowledge of both inductive and migratory properties of human mucosal B cells.

Effects of carotenoids on human immune function

Many epidemiological studies have shown an association between diets rich in carotenoids and a reduced incidence of many forms of cancer, and it has been suggested that the antioxidant properties of these compounds are a causative factor. Attention has focused on the potential role of one specific carotenoid, beta-carotene, in preventing cancer, and numerous publications have described in vitro experiments and animal studies which suggest that not only can this carotenoid protect against the development of cancer, but also several other chronic diseases. Since the immune system plays a major role in cancer prevention, it has been suggested that beta-carotene may enhance immune cell function. Several human trials, using dietary beta-carotene supplementation with a wide range of intakes, have been undertaken to address this hypothesis. The general conclusion of these studies is that this compound can enhance cell-mediated immune responses, particularly in the elderly. The present article will review some of these human studies and, hopefully, complement the reviews of other authors associated with the present symposium, some of whom will also describe work in this area. Potential mechanisms for the effects of carotenoids on immune function will also be reviewed. Finally, possible reasons for the failure of three major prospective studies to demonstrate a beneficial effect of beta-carotene supplementation on lung cancer risk will be discussed.

Peritoneal antigen-presenting cells pulsed in vivo with myelin basic protein induce the suppression of experimental autoimmune encephalomyelitis (EAE) in Wistar rats

Suppression of Experimental Autoimmune Encephalomyelitis (EAE) can be achieved by i.p. administration of soluble myelin basic protein (MBP) in adult Wistar rats before the immunization. In the present work, we analyze the role of peritoneal antigen-presenting cells (APC) in the induction of tolerance to EAE. Peritoneal cells (PC) pulsed in vivo with MBP were obtained from rats that had been intraperitoneally injected 2 h previously with soluble MBP (MBP-PC) and then inoculated in recipient rats before the induction of EAE. Our findings show that the i.p. treatment of the animals with MBP-PC before the immunization was able to diminish the incidence and severity of the disease, reduce the histological alterations, abrogate the proliferative response against MBP and change the pattern of the humoral response to MBP. Moreover, when spleen mononuclear cells (MNC) from tolerant animals were cultured together with spleen MNC from sick animals, a dose-dependent inhibition of the proliferative response was observed, arguing for the presence of a regulatory cell population in the tolerant animals. It is also demonstrated that the MBP-PC are activated and their capability of inducing suppression of EAE is highly associated with the enhanced expression of MHC class II IA molecule. Our results show that peritoneal cells pulsed in vivo with MBP are able to induce tolerance and suggest that the up-regulation of MHC class II on MBP-PC is a necessary event for tolerance induction in our model.

Different binding of NF-Y transcriptional factor to DQA1 promoter variants

Polymorphism in the HLA-DQA1 promoter (QAP) sequences could influence the gene expression through a differential binding of transcriptional factors. Considering the main role played by the Y-box in the transcription, we focused on the QAP4 variants differing for a G vs A transition from the QAP Y-box consensus sequence. Electrophoretic Mobility Shift Assay using the two Y-box sequences was performed to determine whether this mutation could be reflected in an allele-specific binding of transcriptional factors. Indeed, the NF-Y specific band, recognised by supershift experiments, was clearly observed using the Y-box consensus probe but it was barely detectable with the QAP4 one. On the contrary, two other complexes were found to more strongly interact with QAP4 Y-box in comparison to the consensus sequence. The analysis of a selected panel of HLA homozygous lymphoblastoid cell lines by competitive RT-PCR and by Northern blotting revealed that the DQA1 *0401, *0501,*0601 alleles regulated by the QAP4 promoters were less expressed at the mRNA level than the DQA1* 0201 allele regulated by the QAP2.1 variant. In conclusion, these results show an evident reduction of NF-Y binding to the mutated QAP4 Y-box and a decreased mRNA accumulation of the DQA1 alleles regulated by these variants.

Hirschsprung's disease: a search for etiology

In 1967, Okamoto et al suggested that the absence of ganglion cells in Hirschsprung's disease (HD) was attributable to failure of migration of neural crest cells. The earlier the arrest of migration, the longer the aganglionic segment. Since then, this hypothesis generally has been accepted. However, subsequent experiments using mouse models of intestinal aganglionosis indicate that nerve cells may reach the correct position but then fail to develop or survive. An alternative hypothesis has been proposed that the aganglionosis may be caused by failure of differentiation as a result of microenvironmental changes after the migration has occurred. Extracellular matrix proteins are recognized as important microenvironmental factors. It has been shown that enteric neurogenesis is dependent on extracellular matrices, which provide a migration pathway for neural crest-derived cells and promote the maturation of settled neural crest-derived cells. Altered distributions of extracellular matrices have been shown in human HD cases and murine HD models, suggesting the role of extracellular matrices in the pathogenesis of HD. Recent studies suggest that intestinal smooth muscle cells, target cells of enteric neurons, play an important role in guiding and influencing its own innervation. Normal maturation was inhibited in neurons cultured with smooth muscle cells of aganglionic colon in comparison to normal colon. Furthermore, it was demonstrated that levels of neurotrophic factors, crucial in the development and survival of enteric neurons, are decreased in circular muscle layers of aganglionic colon in comparison to normoganglionic colon. The smooth muscle cells of the aganglionic colon may represent an unfavorable microenvironment for neuronal development compared with the normally innervated region. Recently, markedly increased immunoreactivity of major histocompatibility complex (MHC) class II antigens and ICAM-1 was demonstrated in aganglionic bowel, suggesting the immunological mechanisms may be involved in the etiology of HD. Genetic factors have been implicated in the etiology of this condition because HD is known to occur in families and in association with some chromosomal abnormalities. Recent expansion of molecular genetics identified multiple susceptibility genes of HD, including the RET gene, the glial cell line-derived neurotrophic factor gene, the endothelin-B receptor gene, and endothelin-3 gene. Of these, inactivating mutations of the RET gene are the most frequent, occurring in 50% of familial and 15% to 20% of sporadic cases of HD. To date, despite extensive research, the exact etiology of this condition remains poorly understood. The present report describes the authors' current understanding of and recent progress in the etiology of HD.

Immune defense mechanisms of the dental pulp

Defense reactions of the dentin/pulp complex involve a variety of biological systems, in which the immune system plays a pivotal role. The knowledge of the organization and function of pulpal immunocompetent cells has been sparse, but in recent years a significant body of information of immune mechanisms in general has provided a footing for substantial new knowledge of the immune mechanisms of the dental pulp. The identification of pulpal dendritic cells (DCs) has generated research activities which have led to a concept of how an antigenic challenge may evoke a pulpal inflammatory response. Although DCs are not able to identify foreign antigens specifically, they provide necessary signals to activate T-lymphocytes which in turn will orchestrate other immunocompetent cells to mount the local immune defense of the dental pulp. The purpose of this review is to accent the organization and function of pulpal DCs and other tissue and cellular components and to provide a basis for how they may interact to instigate pulpal defense mechanisms.

Diminished monocytic HLA-DR expression and ex vivo cytokine secretion capacity in patients with glioblastoma: effect of tumor extirpation

Severe immunodysregulation on lymphocyte level has been described in patients with glioblastoma and is likely involved into its unfavorable prognosis. Although the major importance of monocytic cells for immunoregulation is well established, only very limited data exist regarding the monocyte status in glioblastoma patients. Here we demonstrate a markedly diminished monocytic HLA-DR expression and ex vivo cytokine secretion capacity (TNF-alpha, IL-1beta, IL-10) as signs for monocyte deactivation in glioblastoma patients but not in patients with astrocytoma. As known in immunocompromised patients from other reasons, monocyte deactivation indicate global immunodepression associated with an enhanced risk of infectious complications. Interestingly, tumor resection resulted in partial recovery from the monocytic deactivation. This suggests that the glioblastoma itself contributed to this phenomenon. However, IL-10 and the active forms of transforming growth factor-beta2 and -beta1, which are produced by glioblastoma cells and known to inhibit monocyte function, were not detectable in plasma in our patients. Moreover, low levels of the adrenocorticotropic hormone and cortisol excluded hypothalamo-pituitary-adrenal axis involvement. So, further investigations are necessary to clarify the mechanism. The demonstrated severe glioblastoma-associated monocytic deactivation may contribute to its unfavorable prognosis. Therefore, monocytes may represent target cells for new adjuvant immunotherapies in glioblastoma.

Residual MHC class II expression on mature dendritic cells and activated B cells in RFX5-deficient mice

Patients with major histocompatibility complex class II (MHC-II) deficiency are known to carry mutations in either the RFX complex or the trans-activator CIITA. While the pivotal role of CIITA for MHC-II gene transcription is supported by the essential absence of MHC-II molecules in CIITA-deficient mice, we demonstrate here that RFX5-/- mice retain expression of MHC-II in thymic medulla, mature dendritic cells, and activated B cells. Nevertheless, RFX5-/- mice develop a severe immunodeficiency due to the lack of MHC-II in thymic cortex, failure of positive selection of CD4+ T cells, and absence of MHC-II on resting B cells and resident or IFNgamma-activated macrophages. This differential requirement for CIITA and RFX5 in subsets of antigen-presenting cells may be specific for the mouse; it may, however, also exist in humans without having been noticed so far.

Differential regulation of expression of the MHC class II molecules RT1.B and RT1.D on rat B lymphocytes: effects of interleukin-4, interleukin-13 and interferon-gamma

Susceptibility to induction of both T helper 1- (Th1) and Th2-mediated autoimmunity is multifactorial and involves genetic linkage to the major histocompatibility complex (MHC) class II haplotype. Brown Norway (BN) rats exposed to mercuric chloride develop a Th2-dependent systemic autoimmunity, whereas Lewis rats, which are highly susceptible to Th1-mediated autoimmunity, develop immune suppression after mercuric chloride exposure. Exposure to mercuric chloride is known to enhance B-lymphocyte expression of the MHC class II molecule RT1.B, predominantly in BN rats. We demonstrate that, in contrast, expression of RT1.D was unmodified on these B cells, whereas both RT1.B and RT1.D were up-regulated on epithelial cells. Regulation of B-cell MHC class II isotype expression was further studied in vitro, using BN rat lymph node (LN) cells. Interleukin-4 (IL-4) strongly enhanced B-cell expression of RT1.B (2.8-fold), whereas RT1.D expression was only slightly, although significantly, modified (1.2-fold). B cells from Lewis rats showed a similar IL-4-induced enhancement of RT1.B expression (2.5-fold), whereas, in contrast, RT1.D expression was unmodified. Exposure of LN cells from BN rats to interferon-gamma induced a moderate increase of B-cell MHC class II expression, predominantly of RT1.B. Strong and rapid enhancement of B-cell RT1.D expression was observed after stimulation by phorbol 12-myristate 13-acetate and ionomycin. Rat IL-13 did not modify B-cell MHC class II expression; however, it induced typical morphological changes in peritoneal macrophages. These experiments demonstrate isotype-specific and strain-dependent regulation of MHC class II expression on rat B lymphocytes, which may be of pathophysiological relevance for the strain-dependent susceptibility for Th1- or Th2-mediated autoimmunity.

Induction of autoimmune prostatitis using liposomes is associated to peritoneal cells activation

PROBLEM

Study and characterization of rat peritoneal cells (PC) involved in the induction of autoimmune prostatitis after the intraperitoneal administration of native extract of accessory glands (RAG) associated with liposomes (RAGL).

METHOD OF STUDY

Induction of the autoimmune response in normal recipients by transferring PC or adherent-PC loaded with RAGL (RAGL-PC), but not with PC loaded with empty liposomes (L-PC). Characterization of the morphology, the ultrastructure, and the phenotype of L-PC or RAGL-PC. Study of the respiratory burst by the nitroblue tetrazolium (NBT) reduction assay after stimulation with phorbol myristate acetate (PMA) in both L-PC and RAGL-PC.

RESULTS

Liposomes attached to the cell surface of the M phi were observed by electron microscopy. FACS analyses showed a similar staining pattern with high expression of Ia molecules on L-PC and RAGL-PC compared with controls. PMA-stimulated L-PC or RAGL-PC markedly reduced the NBT compared with controls.

CONCLUSION

Our results suggest that the effective uptake of liposomes and the initial activation of PC together with a prolonged stimulatory effect help to disrupt the tolerance state. The present experimental model is an interesting approach to further characterize events associated with antigenic presentation when an autoimmune response is triggered.

MHC class II expression on human heart microvascular endothelial cells: exquisite sensitivity to interferon-gamma and natural killer cells

BACKGROUND

Immunocytochemical analysis of human organs in situ reveals differential expression of MHC class II antigens by microvascular endothelial cells (MVEC) and endothelial cells (EC) from large vessels. In view of the role of EC as initiators of allograft rejection, it is of interest to understand the regulation of MHC class II regulation by human MVEC. We have previously isolated, cultured, and characterized MVEC from the human heart, showing that although these cells were initially MHC class II positive, the antigens were lost after about 14 days in culture. These results suggest that basal expression in vivo is maintained by circulating factors.

METHODS

Here we have compared the sensitivity of human heart MVEC, human umbilical vein endothelial cells (HUVEC), and adult large vessel EC (aorta, coronary artery, and pulmonary artery) to interferon (IFN)-gamma and natural killer (NK) cell-mediated induction of MHC class II antigens. MVEC and HUVEC were cultured with 1, 5, 10, 50, 100, and 500 U/ml of IFN-gamma for 4 days, the cells were washed, and flow cytometry was used to examine HLA-DR expression at days 1, 2, 4, 7, 10, 14, and 21. EC were also cultured with purified NK cells in the presence and absence of neutralizing antibodies to IFN-gamma, and MHC class II expression was analyzed.

RESULTS

As little as 5 U/ml of IFN-gamma produced 98% positive cells in heart MVEC compared with 100-500 U/ml needed for the same effect in HUVEC or other large vessel EC (coronary, aorta, pulmonary). Class II expression was maintained longer by MVEC (for 17 days) compared with HUVEC (for 10 days). NK cells and supernatant from MVEC/NK cultures induced MHC class II antigens on MVEC and HUVEC in a dose-dependent fashion; the MVEC showed an enhanced sensitivity compared with the HUVEC. The NK effects were inhibited by neutralizing antibodies to IFN-gamma. The allostimulatory ability of MHC class II-positive EC was shown to be proportional to the amount of MHC class II on the cell surface.

CONCLUSIONS

The results suggest that basal expression of MHC class II on human MVEC is maintained by circulating IFN-gamma and NK cells. This conclusion has implications for therapeutic interventions.

Dietary fish oil enhances circulating interferon-gamma in mice during listeriosis without altering in vitro production of this cytokine

The objective of this study was to investigate the impact of feeding mice a diet rich in n-3 polyunsaturated fatty acids (PUFA) from fish oil on the interferon-gamma (IFN-gamma) response during an active infection with Listeria monocytogenes. Weanling female C3H/Hen mice were fed experimental diets containing 20% by weight one of the following fats: soybean oil, lard, or a mixture of menhaden fish oil and corn oil (17:3, w/w). After 4 weeks, mice were injected with 10(5) live L. monocytogenes, and the concentration of IFN-gamma in serum and spleen was determined 0, 2, 4, and 7 days postinfection by enzyme-linked immunosorbent assay (ELISA). Fish oil-fed mice showed significantly higher IFN-gamma in their blood at 2 and 4 days postchallenge compared with mice fed the soybean oil-containing or lard-containing diets (p < 0.001). A higher concentration of IFN-gamma was also found in the spleen homogenate of fish oil-fed mice on day 4 postchallenge (p < 0.005). To examine in vitro IFN-gamma production, splenocytes were isolated from fish oil-fed and soybean oil-fed mice on day 4 postchallenge and cultured with concanavalin A (1 microgram/ml and 10 micrograms/ml) for 24 and 48 h. There were no significant differences in the IFN-gamma concentration in cell culture supernatants between these diet treatments. This study demonstrated that the elevation in the concentration of IFN-gamma in blood and spleen during murine listeriosis is accentuated and prolonged by dietary n-3 PUFA, and these effects may not be due to changes in IFN-gamma production.

Polymorphism in the 5' terminal region of the mRNA of HLA-DQA1 gene: identification of four groups of transcripts and their association with polymorphism in the alpha 1 domain

Relative to other loci in the MHC, the HLA-DQ locus exhibits an exceptional degree of polymorphism of both A1 and B1 genes, particularly in the region coding for alpha and beta chains. Diversification of the association between different alpha and beta molecules either in cis or in trans contributes to the structural diversity of the repertoire of cell-surface class II protein's in the population. In addition, structural allelic polymorphisms in the 5' regulatory region of both DQB1 and DQA1 shows several linkage groups with respect to the allelic coding sequence of the respective genes. We describe here the allelic polymorphism in the DQA1 mRNA structure located at the 5' untranslated terminal region. This portion of the mRNA molecule represents, in many genes, a cis-acting regulatory sequence playing a role in the posttranscriptional mechanisms by which gene expression can be modulated. Based on detailed transcriptional analysis, we have been able to define at least four groups of transcripts in DQA1. The mRNA variability was associated with the polymorphism of the second exon of the DQA1 gene, coding for the alpha 1 domain and not with the DNA polymorphism in the 5' regulatory region.

The effect of beta-carotene supplementation on the immune function of blood monocytes from healthy male nonsmokers

Although there is strong epidemiologic evidence that diets rich in carotenoids such as beta-carotene are associated with a reduced incidence of cancer, the cellular mechanisms underlying this phenomenon remain unknown. This article describes the effect of dietary beta-carotene supplementation on both the expression of functionally associated surface molecules on human monocytes and on the secretion of the cytokine tumor necrosis factor-alpha (TNF-alpha) by monocytes, all of which are involved in the initiation and regulation of immune responses involved in tumor surveillance. A double-blind, placebo-controlled, crossover study was undertaken in which 25 healthy, adult male nonsmokers were randomly assigned to receive beta-carotene (15 mg daily) or placebo for 26 days, followed by the alternative treatment for a further 26 days. The expression of functionally related monocyte surface molecules was quantified by flow cytometry, and ex vivo secretion of TNF-alpha was quantified by an enzyme-linked immunosorbent assay, before and after each treatment period. After dietary supplementation there were significant increases in plasma levels of beta-carotene and in the percentages of monocytes expressing the major histocompatibility complex class II molecule HLA-DR and the adhesion molecules intercellular adhesion molecule-1 and leukocyte function-associated antigen-3. In addition, the ex vivo TNF-alpha secretion by blood monocytes was significantly increased after supplementation. These findings suggest that moderate increases in the dietary intake of beta-carotene can enhance cell-mediated immune responses within a relatively short period of time, providing a potential mechanism for the anticarcinogenic properties attributed to beta-carotene.

Functional significance of polymorphism among MHC class II gene promoters

The functional significance of polymorphism among MHC class II promoters in man and mouse is here reviewed, mainly in terms of the hypothesis of differential expression. The hypothesis proposes that differences between antigen-presenting cells in MHC class II expression exert a co-dominant effect on the Th1-Th2 cytokine balance, such that class II molecules of one type come to control to a greater extent the production of one group of cytokines, and those of another type the production of the alternative group. The survey deals with the influence of signal strength and antigen-presenting cell type on T-cell subset differentiation; functional differences between MHC class II molecules not obviously related to determinant selection; disease protection mediated by HLA alleles; mechanisms possibly responsible for allotypic and isotypic bias; overdominance (heterozygous advantage) in selection for expression of class II alleles; MHC class II promoter structure and function; inter-locus and inter-allele variability within human MHC class II gene upstream regulatory regions; a comparison of these polymorphisms in mouse and man; read-out of class II promoter function; and a comparison with expression of MHC class I. We conclude that the evidence that this variation is functionally active (i.e. controls expression) is increasing, but is not yet compelling. The crucial test still to come, we suggest, is whether or not the biological effects attributable to this polymorphism will line up with molecular studies on expression.

Protamine enhances the activity of human recombinant interferon-gamma

Recombinant interferon-gamma (IFN-gamma) is a potent immune regulatory cytokine and is involved in the defense against several intracellular organisms, such as Chlamydia and Toxoplasma. Furthermore IFN-gamma is able to inhibit the growth of human tumor cell lines. The ability to inhibit the growth of intracellular organisms makes the therapeutic use of recombinant human IFN-gamma in certain patient groups, such as those with chronic granulomatous disease, leprosy, and HIV infection, very attractive. We have shown recently that IFN-gamma-mediated effects can be blocked by heparin and that this inhibitory effect can be abrogated by the addition of protamine. In this report, we show that the antagonistic effect of protamine on heparin-mediated inhibition of IFN-gamma activity is mainly due to the capacity of protamine to enhance IFN-gamma activity. We found that protamine enhances the capacity of IFN-gamma to inhibit the growth of different brain tumor cell lines, to induce indolamine 2, 3-dioxygenase activity, to induce toxoplasmostasis, and to induce MHC class II antigen expression in human glioblastoma cells and in human native fibroblasts. We were able to demonstrate that IFN-gamma binds to protamine, and, therefore, we assume that the effect of protamine on IFN-gamma is due to a direct interaction between the two molecules.

Dietary fat influences Ia antigen expression, cytokines and prostaglandin E2 production of immune cells in autoimmune-prone NZB x NZW F1 mice

To elucidate further the influences of dietary fat on autoimmune diseases, two groups of NZB/W F1 mice were fed with diets containing 200 g dietary fat/kg and 50 g dietary fat/kg (control) respectively. The difference in energy intake between these two groups was compensated with carbohydrate. Mice were bled regularly every month and some of them were killed for in vitro experiments after 5 months experimental diets. Higher immunoglobulin (Ig)M and IgG anti-double stranded DNA antibody levels, shortened life span and worsened proteinuria were noted in mice fed on the high-fat diet compared with those fed on 50 g dietary fat/kg. Phenotypic analyses of spleen cells and peritoneal exudate cells showed that the percentage of CD5+ B cells and the mean fluorescent intensity of major histocompatibility molecules on the surface of both types of cells were higher in mice fed on the high-fat diet. In general, higher type 2 T-helper cell activity was noted in mice fed on the high-fat diet. In addition, cytokines such as interleukin-6, tumour necrosis factor-alpha and prostaglandin E2 (PGE2) produced by lipopolysaccharide-stimulated peritoneal exudate cells were also higher in the high-dietary-fat group. These studies suggest that high dietary fat and its related PGE2 level might have a critical effect on the frequency of CD5+ B cells, cytokine production, macrophage function and subsequent autoimmune regulation in autoimmune mice.

Regulation of MHC class II genes: lessons from a disease

Precise regulation of major histocompatibility complex class II (MHC-II) gene expression plays a crucial role in the control of the immune response. A major breakthrough in the elucidation of the molecular mechanisms involved in MHC-II regulation has recently come from the study of patients that suffer from a primary immunodeficiency resulting from regulatory defects in MHC-II expression. A genetic complementation cloning approach has led to the isolation of CIITA and RFX5, two essential MHC-II gene transactivators. CIITA and RFX5 are mutated in these patients, and the wild-type genes are capable of correcting their defect in MHC-II expression. The identification of these regulatory factors has furthered our understanding of the molecular mechanisms that regulate MHC-II genes. CIITA was found to be a non-DNA binding transactivator that functions as a molecular switch controlling both constitutive and inducible MHC-II expression. The finding that RFX5 is a subunit of the nuclear RFX-complex has confirmed that a deficiency in the binding of this complex is indeed the molecular basis for MHC-II deficiency in the majority of patients. Furthermore, the study of RFX has demonstrated that MHC-II promoter activity is dependent on the binding of higher-order complexes that are formed by highly specific cooperative binding interactions between certain MHC-II promoter-binding proteins. Two of these proteins belong to families of which the other members, although capable of binding to the same DNA motifs, are probably not directly involved in the control of MHC-II expression. Finally, the facts that CIITA and RFX5 are both essential and highly specific for MHC-II genes make possible novel strategies designed to achieve immunomodulation via transcriptional intervention.

Immunodepression following neurosurgical procedures

OBJECTIVE

To determine the influence of a selective, sterile central nervous system surgery on immune reactivity, particularly whether a decrease of monocytic human leukocyte antigen-DR expression, indicating immunodepression, occurs after neurosurgery and if this measurement is useful for identification of patients with a high risk of infection.

DESIGN

Prospective study.

SETTING

Department of neurosurgery and intensive care unit in a university hospital.

PATIENTS AND INTERVENTIONS

Blood samples were obtained from 46 patients at least once during the first 3 days after undergoing sterile central nervous system surgery. Fourteen of these patients developed infectious complications as defined by clinical and microbiological criteria. In ten of 46 patients, paired samples of blood and cerebrospinal fluid were collected from a ventricle drain at the following times: 1 day before surgery; several times on the day of surgery; and every day after surgery for at least 6 days.

MEASUREMENTS AND MAIN RESULTS

Monocytic human leukocyte antigen-DR expression, as measured by flow cytometry on days 1 through 3 after surgery in 46 patients, was lower in 14 patients who developed infection after neurosurgery (p < .0001). In all ten closely monitored patients, monocytic human leukocyte antigen-DR expression decreased temporarily after surgery. Of these patients, only one patient showed a persistent and considerably decreased monocytic human leukocyte antigen-DR expression. This patient was the only patient in this subgroup who developed sepsis syndrome. In order to assess whether the monocytic human leukocyte antigen-DR decrease was associated with a preceding inflammatory response, local and systemic concentrations of interleukin (IL)-1 beta, IL-6, IL-8, tumor necrosis factor-alpha, and interferon-gamma were measured in this subgroup. These cytokines were not detectable in plasma during the first days after surgery. In contrast, considerable increases of IL-6 and IL-8 concentrations were detectable in cerebrospinal fluid within hours after surgery.

CONCLUSIONS

A decrease of monocytic human leukocyte antigen-DR expression occurs after neurosurgery and is associated with a preceding, strong, intracranial (but not systemic) inflammatory response. A very low monocytic human leukocyte antigen-DR expression (< 30% positive monocytes) suggests the possibility of infection. Measurement of monocytic human leukocyte antigen-DR expression could help to detect patients with a high risk of infection after neurosurgery. Our results suggest that even sterile central nervous system surgery may contribute to general immunodepression. The local intracranial inflammatory response may be involved in this process.

Overexpression of intercellular adhesion molecule-1 (ICAM-1) and MHC class II antigen on hypertrophic nerve trunks suggests an immunopathologic response in Hirschsprung's disease

The pathogenesis of Hirschsprung's disease (HD) is not fully understood. The authors studied expression of intercellular adhesion molecule-1 (ICAM-1) and major histocompatibility complex (MHC) class II antigen in the resected bowel specimens of 18 patients with HD who had no evidence of enterocolitis and in eight age- and site-matched controls, using indirect immunohistochemistry. There was strong expression of ICAM-1 and MHC class II antigen on hypertrophic nerve trunks, in both the submucous and myenteric plexuses of the aganglionic colon. The transition zone showed strong expression of ICAM-1 and MHC class II antigen on small ganglia in the myenteric and submucous plexuses. However, no staining of ganglia or nerve fibers was found in the submucous and myenteric plexuses of the colon from controls or in the ganglionic colon from patients with HD. The expression of both antigens on hypertrophic nerve trunks suggests the presence of an immunologic response in the pathogenesis of HD.

Molecular defects in the bare lymphocyte syndrome and regulation of MHC class II genes

The complex pattern of expression of major histocompatibility complex (MHC) class II molecules plays an essential role in the control of the immune response. Our understanding of the molecular mechanisms controlling this expression has benefited greatly from the identification of the regulatory factors defective in two forms of a hereditary disease of MHC class II regulation: bare lymphocyte syndrome. This has also provided new tools for the experimental modulation of MHC class II expression.

Complementation cloning of mammalian transcriptional regulators: the example of MHC class II gene regulators

Cloning by complementation of mutant cell lines is a powerful way in which to identify and isolate important regulatory genes on the basis of functional assays. The recent cloning of two essential regulators of major histocompatibility complex (MHC) class II gene expression has not only advanced our understanding of the complex mechanisms controlling these genes, but also helps to illustrate the feasibility of this approach for the study of mammalian gene regulation.

The biology of airway dendritic cells

Recent work from our laboratory has identified a network of constitutively class II MHC (Ia) bearing dendritic cells (DC) within the epithelium of the conducting airways of laboratory animal species and in humans. The density of DC within the respiratory tract is highest in those areas exposed to greater amounts of inhaled antigen and further work has identified these DC as being critically important in controlling the induction of immune responses within the airways. The DC population in the airway epithelium is renewed every 48-72 h; this represents a more rapid turnover than DC in other tissues which are exposed to a smaller antigenic load. In addition to these results we will discuss other work which shows that airway DC are a very reactive population, comparable with neutrophils in their response to acute inflammatory stimuli and that their numbers and Ia content can be modulated following exposure to topical and systemic steroids. Finally we will discuss the development of these cells after birth and how this may influence the pathogenesis of immune regulated diseases such as asthma and allergic rhinitis.

Expression of HLA class II antigens in marginal periodontitis of patients with Down's syndrome

The expression of HLA Class II antigens on the surfaces of immunocompetent cells and the presence of CD1a+ cells (Langerhans cells) are important components of antigen presentation. Quantitative variations in HLA class II expression on antigen-presenting cells play a role in immune regulation. An indirect immunofluorescent technique was used on cryostat sections to reveal such differences qualitatively or quantitatively between chronic marginal periodontitis (CMP) in patients with Down's syndrome (DS) and in otherwise normal patients (NP). We found increased frequency of HLA Class II (HLA-expression on inflammatory cells and on keratinocytes of the oral gingival epithelium) in CMP of DS patients compared to sections from NP. The expression of HLA-DR was more frequent on the keratinocytes of the pocket epithelium in NP than in DS. There were significantly higher numbers of CD1a+ cells and ratios of HLA-DR+/CD1a+ cells and HLA-DP+/CD1a+ cells in the DS group compared to the NP group. Our conclusion is that there is a more pronounced inflammatory process in the gingival sites with CMP of DS patients compared to CMP in NP. The findings also indicate that there is a highly activated immune response in CMP of DS patients.

The inhibitory effects of Mycobacterium tuberculosis on MHC class II expression by monocytes activated with riminophenazines and phagocyte stimulants

The expression of MHC class II antigens by peripheral blood monocytes from normal individuals was investigated. Class II expression as determined by a cell ELISA was effectively induced by various phagocyte stimulants. A further aspect of our study investigated the effects of clofazimine, a riminophenazine antimicrobial agent and its analogue, B669, on class II expression. Both agents at concentrations attainable in vivo increased the expression of MHC class II antigens. A 25-kD glycolipoprotein derived from Mycobacterium tuberculosis that inhibits phagocyte functions has previously been described. This component significantly reduced the expression of MHC class II antigens induced by the riminophenazines, clofazimine and B669, interferon-gamma (IFN-gamma) or opsonised yeast when added at the initiation of experiments. The riminophenazines could not restore the decrease in class II antigen expression previously inhibited by the 25-kD mycobacterial fraction. However, cultures prestimulated with the riminophenazines or phagocyte stimulants were unaffected by the 25-kD mycobacterial fraction. The results suggest the potential use of these agents as modulators of phagocyte function.

The effect of IL-4 on antigen expression: a comparison of fluorescence intensity and antigen density

We have compared the membrane expression of MHC class II antigen and Ig on murine splenic B lymphocytes by two flow cytometric methods. The first method, commonly used, determined the mean immunofluorescence intensity; the second measured antigen density as a ratio of mean fluorescence intensity to cell volume. The data generated by the two methods allow for different interpretations of antigen density in comparison to antigen expression. By mean fluorescence intensity, activated B lymphocytes expressed more MHC class II antigen and membrane Ig than did resting B cells. However, resting B cells had the same density of MHC class II antigen and membrane Ig as activated B cells. Next we examined the effect of IL-4 on antigen expression by the two methods. We found that although IL-4 increased the mean fluorescence intensity and density of MHC class II and membrane Ig on each B cell population, the density of expression of membrane Ig tended to be greater on the resting B cells than on the activated, while the density of MHC class II antigen was essentially the same on each of the IL-4 treated B cell populations.

Biological implications of HLA-DR expression in tumours

HLA-DR antigens show restricted tissue distribution in comparison with the more extensive expression of HLA class I molecules. This constitutive expression is genetically controlled by well-defined mechanisms. In addition, DR antigen expression can be induced by a variety of cytokines through different molecular genetic events that convert DR-negative epithelia into positive cells. In this review we analyse the two major pathological situations in which abnormal DR expression occurs: autoimmune diseases and tumour development. We hypothesize that conversion to DR-positivity may produce two opposite effects in both clinical situations: (1) a useful one in tumours associated with a good prognosis; and (2) a harmful one in autoimmune diseases with increased tissue damage.

Antigenaemia during acute graft versus host disease

AIMS

Animal studies have shown that antigens present within the gut play an important role in the development of acute graft versus host disease (GvHD) following allogeneic bone marrow transplantation (BMT). In previous studies, inert sugars have been found to penetrate the small bowel mucosa after conditioning therapy for BMT; endotoxaemia can also occur during acute GvHD. Data on absorption of antigenic proteins across the gut following BMT in humans have not been presented as yet.

METHODS

Six patients undergoing allogeneic BMT were studied to determine whether enteric ovalbumin absorption increased or endotoxaemia developed during acute GvHD.

RESULTS

Three patients had minimal antigenaemia and no detectable endotoxaemia before receiving conditioning therapy. At the onset of acute GvHD, however, much higher ovalbumin concentrations were detected in those patients with severe antigenaemia. Serum concentrations of specific antiovalbumin IgG and IgA, or antiendotoxin IgM or IgG had no bearing on detectable IgG or IgM ovalbumin or endotoxin concentrations. In five of six patients, small bowel permeability increased, as tested by the lactulose/mannitol sugar absorption test, but detectable ovalbumin absorption increased in only three of these and only two developed endotoxaemia.

CONCLUSIONS

Antigens present within the gut can cross the mucosal epithelium during acute GvHD, probably resulting in an enhanced immune response.

Polymorphism in both X and Y box motifs controls level of expression of HLA-DRB1 genes

The HLA class II antigens of the human major histocompatibility complex play an important role in immune response. The quality of the immune response is determined not only by polymorphisms in their coding region, but also by the level of their cell-surface expression which affects, for example, the extent of T-cell activation. We have previously described allelic polymorphisms in the upstream regulatory regions of HLA-DRB genes, which affected DNA-protein interactions and resulted in significantly different promoter strengths. In the present study, we investigated the effect of polymorphisms in the X and Y box motifs on the transcriptional activity of DRB1 gene promoters in the DR1, DR51, and DR53 haplotype groups. We used normal, chimeric, and mutated DRB promoters and compared their relative abilities to initiate transcription of the CAT reporter gene in human B-cell lines. The results show that polymorphisms in both the X1 and Y box motifs play a dominant role in the promoter strength. In the gel mobility shift assay, we observed differential ability of nuclear proteins that bind to the polymorphic X1 and Y box elements. The results in the present study confirm earlier data in that the nucleotide variation in the X1 box affects the level of expression of DRB1 genes. In addition, the present data demonstrate that polymorphism in the Y box, which affects the inverted CCAAT sequence, also plays a dominant role in the transcriptional activity of DRB1 promoters.