Regulation of murine macrophage Ia-antigen expression by products of activated spleen cells

Protective role of spleen-derived macrophages in lung inflammation, injury, and fibrosis induced by nitrogen mustard

Nitrogen mustard (NM) is a vesicant that causes lung injury and fibrosis, accompanied by a persistent macrophage inflammatory response. In these studies we analyzed the spleen as a source of these cells. Splenectomized (SPX) and sham control rats were treated intratracheally with NM (0.125 mg/kg) or PBS control. Macrophage responses were analyzed 1-7 days later. Splenectomy resulted in an increase in lung macrophages expressing CCR2, but a decrease in ATR-1α(+) cells, receptors important in bone marrow and spleen monocyte trafficking, respectively. Splenectomy was also associated with an increase in proinflammatory M1 (iNOS(+), CD11b(+)CD43(+)) macrophages in lungs of NM-treated rats, as well as greater upregulation of iNOS and COX-2 mRNA expression. Conversely, a decrease in CD11b(+)CD43(-) M2 macrophages was observed in SPX rats, with no changes in CD68(+), CD163(+), CD206(+), or YM-1(+) M2 macrophages, suggesting distinct origins of M2 subpopulations responding to NM. Macrophage expression of M2 genes including IL-10, ApoE, PTX-2, PTX-3, 5-HT2α, and 5-HT7 was also reduced in NM-treated SPX rats compared with shams, indicating impaired M2 activity. Changes in lung macrophages responding to NM as a consequence of splenectomy were correlated with exacerbated tissue injury and more rapid fibrogenesis. These data demonstrate that the spleen is a source of a subset of M2 macrophages with anti-inflammatory activity; moreover, in their absence, proinflammatory/cytotoxic M1 macrophages predominate in the lung, resulting in heightened pathology. Understanding the origin of macrophages and characterizing their phenotype after vesicant exposure may lead to more targeted therapeutics aimed at reducing toxicity and disease pathogenesis.

Superantigens: mechanisms by which they may induce, exacerbate and control autoimmune diseases

Superantigens are polypeptide molecules produced by a broad range of infectious microorganisms which elicit excessive and toxic T-cell responses in mammalian hosts. In light of this property and the fact that autoimmune diseases are frequently the sequelae of microbial infections, it has been suggested that superantigens may be etiologic agents of autoreactive immunological responses resulting in initiation, exacerbation or relapse of autoimmune diseases. This article relates the biology of superantigens to possible mechanisms by which they may exert these activities and reviews the evidence for their roles in various human and animal models of autoimmune disease. Finally, a mechanism of active suppression by superantigen-activated CD4+ T-cells that could be exploited for therapy as well as prophylaxis of human autoimmune diseases is proposed.

Graft-versus-host disease and the Th1/Th2 paradigm

Graft-versus-host disease (GVHD) is the major complication after allogeneic bone marrow transplantation (BMT) and is initiated by alloreactive donor T cells recognizing foreign histocompatibility antigens of the host. There is now substantial experimental and clinical evidence to implicate a dysregulation of cytokine networks as a primary cause for the induction and maintenance of GVHD. In this article, current knowledge of the involvement of cytokines in GVHD is reviewed. The balance between type 1 cytokines (interleukin-2, interferon-gamma) and type 2 cytokines (interleukin-4, interleukin-10) is hypothesized to govern the extent to which a cell-mediated immune response and a systemic inflammatory response develop after allogeneic BMT. Because type 2 cytokines can inhibit the production of the proinflammatory cytokines interleukin-1 and tumor necrosis factor-alpha, a type 1 to type 2 shift in the initial response of donor T cells to host alloantigens may interrupt the cytokine cascade after allogeneic BMT and may offer a new approach to the prevention and treatment of acute GVHD. Interventions to specifically eliminate or modify the response of donor T cells to alloantigens in order to reduce GVHD may obviate the need for T cell depletion in clinical BMT and thus avoid the increased risk of relapse of malignancy and impairment of donor cell engraftment.

Polytuftsin: its possible effects and mechanism during macrophage activation

Polytuftsin (PT) a 35-40 repeat unit of tuftsin (TKPR), when administered as a conjugate with the malarial peptide, ring-infected erythrocyte surface antigen (RESA), enhanced antigen-induced lymphoproliferation and antibody levels in mice as compared to RESA alone. This enhancement was unrelated to the H-2 background of the animals. The present study was undertaken with a view to understanding the mechanism(s) responsible for this immune enhancement. Peritoneal adherent cells (PAC) from H-2b and H-2d mice were incubated with RESA alone, PT-conjugated RESA, a physical mixture of RESA + PT and PT alone. They were subsequently evaluated for I-A expression using monoclonal antibodies and flow cytometry as well as cell-ELISA. Significant increase in I-A expression on PAC was observed in all 4 groups as compared to untreated cells. Whereas cells treated with PT-conjugated RESA showed highly significant increase in I-A (P < 0.001), the other groups showed moderate increase (P < 0.05). This enhancement was attributable to increase in the number of I-A-positive cells rather than I-A molecules per cell. Moreover, IL-1 release, as assayed by bioassay, was significantly higher in cells treated with conjugated RESA as compared to cells treated with RESA or PT alone (P < 0.05). Thus, it would appear that PT-conjugated RESA peptide of the malarial antigen selectively enhances major histocompatibility complex (MHC) class II molecules on antigen-presenting cells (APC) and may therefore improve immune functions by stimulating better antigen presentation and proliferation of T cells.

Inhibition of macrophage inducible protein expression by delta-9-tetrahydrocannabinol

Macrophages have been shown to undergo a sequential process to full activation in response to priming and triggering signals such as gamma interferon (IFN gamma) and bacterial lipopolysaccharide (LPS). These cells also may be driven directly to full activation by exposure to relatively high concentrations of LPS. Each of the stages to activation is associated with differential protein expression suggesting that newly synthesized proteins are associated with the functional activities attributable to that activation state. These observations indicate that protein profiles may serve as a barometer of the macrophage activation state. Delta-9-tetrahydrocannabinol (THC), the major psychoactive component in marijuana, was shown to inhibit inducible protein expression in response to the priming agents Concanavalin A (Con A) supernatant and IFN gamma. THC also suppressed protein expression in response to LPS. P388D1 and RAW264.7 macrophage-like cells, treated with Con A supernatant or IFN gamma, exhibited restructuring of protein profiles based on iso-Dalt two-dimensional gel electrophoresis. Protein profile restructuring, distinctive from that elicited in response to priming agents, was seen for macrophages treated with LPS. Treatment of macrophages with Con A supernatant, IFN gamma, or LPS in concert with THC (10(-7) M to 10(-5) M), resulted in the generation of protein profiles whose patterns reverted approximately to those of unprimed or unactivated macrophages. THC was shown to alter the expression of select proteins whose induction is associated with macrophage priming or activation. The expression of P388D1 macrophage class II Ia molecules of the major histocompatibility complex (MHC), in response to Con A supernatant and IFN gamma, was inhibited. THC also altered the expression of tumor necrosis factor alpha (TNF alpha) elicited by RAW264.7 cells in response to LPS. These results suggest that THC alters macrophage functional activities, at least in part, by suppressing their capacity to express effector molecules elicited in response to priming and activating signals.

Modulation of bullous pemphigoid antigen gene expression by gamma-interferon in cultured keratinocytes

Bullous pemphigoid (BP) is characterized by the production of autoantibodies against BP antigens. gamma-interferon (gamma-IFN), a T-cell lymphokine, is known to enhance the expression of several cell-surface proteins. In this study, keratinocytes were cultured in the presence of gamma-IFN, the expression of BP antigen protein was examined by flow cytometry and BP antigen messenger RNA (mRNA) (encoding 230-kDa protein) was quantified by slot-blot hybridization. The results indicated that BP antigen gene expression by keratinocytes was upregulated by gamma-IFN. This enhancement of gene expression was detected at both the protein and mRNA level, suggesting pretranslational regulation. These results imply the involvement of not only humoral immunity but also cell-mediated immunity in the development of BP.

The extracellular domain of the human interferon gamma receptor interacts with a species-specific signal transducer

At least two species-specific gene products are required for signal transduction by interferon gamma (IFN-gamma). The first is the IFN-gamma receptor, which binds ligand with high affinity in a species-specific manner. The second is an undetermined species-specific signal transducer(s). To determine whether the human IFN-gamma receptor (hIFN-gamma R) interacts directly with this signal transducer(s) and, if so, with what functional domain(s), we constructed expression vectors for the hIFN-gamma R and three hybrid human-murine IFN-gamma receptors. The hybrid receptors contained the extracellular, human IFN-gamma (hIFN-gamma) binding domain of the hIFN-gamma R, either the human or murine transmembrane domain, and either the human or murine intracellular domain. The vectors encoding these receptors were stably transfected into two mouse cell lines, one of which (SCC-16-5) contains a single copy of human chromosome 21. The resulting cell lines were treated with hIFN-gamma, and murine major histocompatibility complex class I antigen expression was analyzed by immunofluorescence flow cytometry. All transfected cell lines lacking human chromosome 21 remained insensitive to hIFN-gamma. However, all four of the IFN-gamma receptors were able to signal when expressed in the cell line containing human chromosome 21. We conclude that the extracellular domain of the IFN-gamma receptor is involved not only in the species specificity of IFN-gamma binding but also in signalling through interaction with an as yet unidentified species-specific factor(s) encoded by a gene(s) on human chromosome 21.

The extracellular domain of the human interferon gamma receptor interacts with a species-specific signal transducer

At least two species-specific gene products are required for signal transduction by interferon gamma (IFN-gamma). The first is the IFN-gamma receptor, which binds ligand with high affinity in a species-specific manner. The second is an undetermined species-specific signal transducer(s). To determine whether the human IFN-gamma receptor (hIFN-gamma R) interacts directly with this signal transducer(s) and, if so, with what functional domain(s), we constructed expression vectors for the hIFN-gamma R and three hybrid human-murine IFN-gamma receptors. The hybrid receptors contained the extracellular, human IFN-gamma (hIFN-gamma) binding domain of the hIFN-gamma R, either the human or murine transmembrane domain, and either the human or murine intracellular domain. The vectors encoding these receptors were stably transfected into two mouse cell lines, one of which (SCC-16-5) contains a single copy of human chromosome 21. The resulting cell lines were treated with hIFN-gamma, and murine major histocompatibility complex class I antigen expression was analyzed by immunofluorescence flow cytometry. All transfected cell lines lacking human chromosome 21 remained insensitive to hIFN-gamma. However, all four of the IFN-gamma receptors were able to signal when expressed in the cell line containing human chromosome 21. We conclude that the extracellular domain of the IFN-gamma receptor is involved not only in the species specificity of IFN-gamma binding but also in signalling through interaction with an as yet unidentified species-specific factor(s) encoded by a gene(s) on human chromosome 21.

Selective induction of B7/BB-1 on interferon-gamma stimulated monocytes: a potential mechanism for amplification of T cell activation through the CD28 pathway

The B cell activation antigen B7/BB-1 is the natural ligand for the T cell antigen CD28 and these two molecules are capable of mediating T-B cell adhesion. Engagement of the CD28 pathway provides a costimulatory signal to T cells leading to enhanced lymphokine production. We report that interferon-gamma (INF-gamma) induces the expression of B7/BB-1 on monocytes. This induction was very specific since other cytokines and stimuli which activate monocytes including M-CSF, GM-CSF, IL3, TNF-alpha, and LPS were unable to induce B7/BB-1. Following culture of monocytes with INF-gamma, maximal mRNA and cell surface B7/BB-1 expression was detected at 12 and 24 hr, respectively. In addition to antigen presentation, optimal T cell activation and lymphokine synthesis require an additional cell to cell contact signal provided by the antigen presenting cell. The induction of B7/BB-1 on monocytes and subsequent heterophilic interaction of B7/BB-1 with CD28 may provide a mechanism for the amplification of T cell proliferation and lymphokine production by INF-gamma activated monocytes.

Reversal of immune dysfunction in osteopetrotic rats by interferon-gamma: augmentation of macrophage Ia expression and lymphocyte interleukin-2 production and proliferation

Lymphocytes from osteopetrotic (op) rats, compared to their normal (n) littermates, exhibit defective immune functions associated with their inability to resorb bone. Among these immune defects are the failure of their spleen cells to proliferate normally to mitogens and to generate IL-2. Addition of exogenous IL-2 failed to reverse the suppressed proliferation in the op spleen cells, indicating that additional defects were involved in the suppression. Phenotypic analysis of cellular constituents of op and n spleens revealed that the percentages of T cells, macrophages, and IL-2 receptor positive cells were not different. Furthermore, there was no difference in CD4 (W3/25) and CD8 (OX8) cells. However, the Ia+ (OX3) cells in the op spleen represented less than 50% of those found in the n spleen, but the op had higher levels of transferrin receptor (OX26). On the basis of the ability of interferon-gamma (IFN-gamma) to increase Ia expression, this cytokine was added to op spleen cells (10-50 U/ml) and found to increase the number of Ia+ cells to the level found in n spleen cells. Moreover, pretreatment of op spleen cells with IFN-gamma restored their ability to proliferate to mitogens and their responsiveness to IL-2. Not only did IFN-gamma reverse the defective response to IL-2, but it also augmented the defective IL-2 production by op spleen cells. Taken together, these findings demonstrate that IFN-gamma can reverse many of the impaired immune functions characteristic of op spleen cells in vitro. Furthermore, these data suggest that IFN-gamma may provide an important avenue of treatment in these animals that may contribute to restoration of normal bone resorption.

A cluster of transcribed sequences between the Pb and Ob genes of the murine major histocompatibility complex

The region of the murine major histocompatibility complex (MHC) between the Pb (A beta 3) and Ob (A beta 2) genes controls the expression of an intracellular complex named the LMP (low molecular weight polypeptide) complex. DNA probes for at least seven different genes mapping to this region were isolated. These hybridize to a minimum of eight different transcripts ranging from approximately 1.3 to 3.7 kilobases (kb). The deduced amino acid sequences of the corresponding cDNAs indicate that three of these genes are new members of the MHC class II gene family. These genes are transcribed in a tissue-specific pattern similar to that of the traditional class II genes. Two of the remaining four genes, HAM1 and HAM2, are homologous to one another and to a family of eukaryotic and prokaryotic transport proteins and may be involved in antigen processing. The tissue distribution of HAM1 transcripts is consistent with its proposed role in class I-restricted antigen processing, whereas HAM2 transcription appears more restricted and may be involved in antigen processing for class II-restricted T cells. The HAM2 gene may produce two differentially spliced transcripts. The identity of the remaining two genes is not known. Analyses of transcript sizes, tissue distribution, sequence, and genetic mapping data suggest that none of these genes code for LMP antigens.

Placental MHC class I antigen expression is induced in mice following in vivo treatment with recombinant interferon-gamma

Allogeneically pregnant mice (NFR/N (Swiss-derived) H2q x 57/B1 H2b) were injected daily from day 11 to 18 of gestation with recombinant rat interferon-gamma (IFN-gamma) and the effects on placental MHC antigen expression were evaluated by immunohistochemistry. The results demonstrated that a daily dose of 200,000 U/mouse induces a significant increase in placental MHC class I expression in the decidua and the basal zone spongiotrophoblast as well as the fetal mesenchyme, while the labyrinthine trophoblast was almost completely MHC negative. No significant induction of MHC class II antigen expression was observed in the placental tissue, with the exception of a few scattered cells. The MHC class II-inducing efficiency of the treatment protocol used was ascertained by staining maternal skin (ear), which proved to contain considerably elevated numbers of MHC class II-positive cells (mainly keratinocytes). The IFN-gamma treated group showed a higher incidence of fetal resorptions than the corresponding controls, but this was probably due to a non-specific toxic effect of the treatment as none of the sera analysed contained detectable amounts of anti-paternal antibodies, no infiltrating lymphocytes were detectable on histological examination of placental sections, and most of the IFN-gamma treated animals successfully completed their pregnancy.

Parasite-accessory cell interactions in theileriosis. Antigen presentation by Theileria annulata-infected macrophages and production of continuously growing antigen-presenting cell lines

Theileria annulata, a protozoan parasite of cattle, infects major histocompatibility complex (MHC) class II+ cells, particularly macrophages, and transforms them into continuously growing cell lines. We examined the effects of parasitism by T. annulata on antigen-presenting cell function. T. annulata-infected cells (TaH) presented ovalbumin (as measured by [3H]thymidine incorporation) to both resting autologous bovine T cells and ovalbumin-specific bovine CD4+ T cell lines. However, the former cells were also stimulated by TaH without exogenous antigen although to a lesser degree than in the presence of antigen. This "nonspecific" proliferation was not seen with the ovalbumin-specific T cell lines. The magnitude of response by resting T cells in the presence of antigen, to TaH or purified peripheral blood monocytes, was essentially similar. However, on a per cell basis fewer TaH were required. Considerably greater proliferation to antigen was seen with the ovalbumin-specific T cell lines in the presence of TaH compared to monocytes and again fewer TaH were required to elicit a response. The kinetics of processing did not appear to be substantially altered in TaH and the increased proliferation may be due to the elevated MHC class II expression of these cells. Genetic restriction studies with the T cell lines indicated that the restricting elements used to present ovalbumin by TaH were the same as those used by monocytes, as identified by an isoelectric focusing technique. The continuously growing cell lines provide us with a unique model for investigating parasite-accessory cell interactions in theileriosis. The augmented antigen presenting cell activity of TaH may play an important role in the pathogenesis of the disease. TaH will also provide us with a valuable resource for our antigen presentation studies. In particular, the enhanced antigen presentation by TaH enabled us to detect responses to lower levels of antigen, often an important consideration for experiments where the quantity of antigen available is the major limiting factor.

Infiltrating mononuclear cells in salivary glands and kidneys in autoimmune MRL/Mp-lpr/lpr mice express IL-2 receptor and produce interferon-gamma

The salivary gland inflammatory lesions and renal vasculitic lesions of autoimmune MRL/lpr mice were analyzed for the presence of activated lymphocytes. Immunohistologic analysis revealed that the majority of lymphocyte-like cells in salivary glands and kidneys expressed CD4 antigen (greater than 50%). Lesser numbers of interleukin-2 receptor (IL-2R) expressing and interferon-gamma (IFN-gamma)-producing cells were present (1-5%). CD4+, IL-2R+, and IFN-gamma + mononuclear cells were found in small inflammatory foci. In larger inflammatory foci the IFN-gamma-producing cells were detected in the periphery in comparable numbers as the IL-2R expressing cells although with different location. Large numbers of cells in the inflammatory foci also expressed MHC Class II molecules (greater than 50%). The expression of IL-2R and production of IFN-gamma in the tissue lesions indicate presence of activated inflammatory T cells. Production of IFN-gamma by the infiltrating mononuclear cells may induce Class II antigens on epithelial cells and stimulate further T cell migration into the inflammatory site.

IL-4 production by T depleted cells from Nippostrongylus brasiliensis infected mice

Interleukin-4 (IL-4) is known to be involved in both the in vivo IgE response and the elevated B cell IgE Fc receptor (Fc epsilon R11) expression seen after a parasite infection. To further analyze the relationship between Fc epsilon R11 expression and IL-4 production, purified B cells from uninfected, Nippostrongylus brasiliensis (Nbr) infected and from goat anti-mouse IgD (GaM delta) injected mice were isolated on various days post-treatment. The Fc episolon R11 levels on purified B cells from normal mice decreased after an overnight culture in media alone and addition of IL-4 to these cultures resulted in a 4 to 13-fold enhancement of Fc epsilon R11 levels. In contrast, the Fc epsilon R11 levels on B cells from Nbr infected mice were elevated after an overnight culture in media alone and addition of IL-4 did not further enhance the already upregulated Fc epsilon R11 levels. Overnight culture of purified B cell blasts from Nbr infected mice in the presence of an anti-IL-4 monoclonal antibody (11B11) caused the elevated Fc epsilon R11 levels to return to levels seen in normal mice, without affecting the Fc epsilon R11 levels on purified Go or B cell blasts from uninfected mice or Go B cells from Nbr infected mice. 11B11 also inhibited the elevated Fc epsilon R11 levels on highly purified B cells obtained by FACS sorting the non-adherent spleen cell population for class II+ cells. In contrast to Nbr infection, the Fc epsilon R11 levels on B cells were downregulated in the GaM delta injected mice. However, analogous to the Nbr system, the Fc epsilon R11 levels were unresponsive to the addition of exogenous IL-4. This study indicates that IL-4 production is seen in T depleted splenocytes and that this alternate source of IL-4 serves to maintain the elevated Fc epsilon R11 levels on B cells.

Antigen presentation by B cells and macrophages of cytochrome c and its antigenic fragment when conjugated to the surface of liposomes

An in vitro antigen presentation system was used to study how antigens coupled to the surface of phospholipid vesicles (liposomes) are presented to antigen specific T cells. Liposome-bound pigeon cytochrome c (PCC) was 30-40-fold more potent than free PCC when peritoneal macrophages were the presenting cell. B cells presented surface-bound PCC, albeit less efficiently than unmodified PCC. Surface-bound peptide epitope was presented by both cell types, but not as efficiently as unmodified peptide. With the T cell epitope, antigen processing was not required since glutaraldehyde fixed cells could present surface-bound peptide.

Modulation of macrophage Ia expression by lipopolysaccharide: stem cell requirements, accessory lymphocyte involvement, and IA-inducing factor production

The mechanism of induction of murine macrophage Ia expression by lipopolysaccharide (LPS) was studied. Intraperitoneal injection of 1 microgram of LPS resulted in a 3- to 10-fold increase in the number of IA-positive peritoneal macrophages (flow cytometry and immunofluorescence and a 6-to 16-fold increase by radioimmunoassay. The isolated lipid A moiety of LPS was a potent inducer of macrophage Ia expression. Ia induction required a functional myelopoietic system as indicated by the finding that the response to LPS was eliminated in irradiated (900 rads) mice and reinstated by reconstitution with bone marrow cells. Comparison of LPS-induced Ia expression in normal and LPS-primed mice revealed a faster secondary response to LPS. The memory response could be adoptively transferred to normal mice with nonadherent spleen cells prepared 60 days after LPS injection. Spleen cells prepared 5 days after LPS injection caused Ia induction in LPS-nonresponder mice; such induction was not observed in irradiated (900 rads) recipients. The cell responsible for this phenomenon was identified as a Thy-1+, immunoglobulin-negative nonadherent cell. The biosynthesis and expression of Ia were not increased by direct exposure of macrophages to LPS in vitro. Small amounts of LPS inhibited Ia induction by gamma interferon. LPS showed positive regulatory effects on Ia expression by delaying the loss of Ia expression on cultured macrophages and by stimulating the production of Ia-inducing factors. Supernatants from cultured spleen cells stimulated with LPS in vitro contained antiviral and Ia-inducing activity that was acid labile, indicating that the active factor is gamma interferon. We conclude that induction of Ia expression by LPS in vivo is a bone-marrow-dependent, radiation-sensitive process which involves the stimulation of a gamma interferon-producing accessory lymphocyte and a delay in Ia turnover.

Intracellular competition for component chains determines class II MHC cell surface phenotype

Mixed isotype (E alpha A beta and A alpha E beta) dimers are not found on Ia+ hematopoietic cells, although some pairs (e.g., E alpha A beta d) reach the membrane of transfected cells expressing only the two relevant class II genes. To examine the basis for this difference in potential versus actual Ia molecule expression, we utilized an L cell transfection model more closely resembling the normal condition of multiple class II alpha and beta chain synthesis within a single cell, such that competition among alpha and beta chains could occur. The surface expression of individual Ia dimers was compared with the available class II chains in such cells. Our data indicate that 3- to 5-fold preferences in assembly or transport of the predominant A alpha A beta and E alpha E beta species preclude expression of the mixed isotype E alpha A beta pair under physiologic conditions of balanced chain synthesis, but that asymmetric chain synthesis can lead to the expression of such mixed dimers on the cell surface in biologically significant amounts.

Improvement of an ELISA bioassay for the routine titration of murine interferon-gamma

We improved an ELISA bioassay for murine IFN-gamma (MuIFN-gamma) based on measurement of Ia antigen on P388D1, a mouse macrophagic tumour line. Cells were cultured in microtitre plates in medium containing dilutions of IFN-gamma source. They were then washed and stained with a rat anti-mouse I amAb followed by mouse anti-rat peroxidase-labelled antibody. After incubation with substrate, the OD was read directly from microtitre plates. Standard curves obtained with reference NIH MuIFN-gamma showed that this assay allowed for the definition of unit values (giving 50% of the maximal effect) comparable to NIH international units (IU). It detected as low as 0.2 IU/ml of MuIFN-gamma and, in contrast to antiviral assays, was insensitive to IFN-alpha/beta. We used a concanavalin A-conditioned supernatant, which is a mixed source of lymphokines, to assess the specificity of our assay. Indeed, Ia expression induced by ConA-conditioned supernatant was fully inhibited by preincubation with anti-MuIFN-gamma antibodies. Using a stable indicator cell line, the present cell surface assay is easier to perform than other ELISA using bone-marrow-derived macrophages, and does not require cell fixation; its high sensitivity and specificity are comparable to that of immunoradiometric assays. It is thus valuable for routine MuIFN-gamma quantitations in culture supernatant and biological fluids.

Antigen presentation by neonatal murine spleen cells

The ability of murine neonatal spleen cells to present soluble antigen to T-helper cells and to produce growth factors in response to subsequent cellular interactions was studied. The T-helper-cell line (D10-G4.1) (D10), which is specific for the soluble antigen conalbumin presented on H-2-matched (H-2k) antigen-presenting cells, was used as cooperating and indicator cells in these cellular interactions. The D10 cells are TH2 T-helper cells which secrete the autocrine growth factor IL-4 and can also respond to exogenous IL-2 (T. R. Mosmann and R. L. Coffmann, Immunol. Today 8, 223, 1987). D10 cells require exogenous IL-1 for their proliferation and secrete, in addition to IL-4, IL-1 inducer factor and GM-CSF. The ability of neonatal spleen cells to present antigen and to stimulate D10 cells to produce IL-4 and proliferate is low. During antigen presentation there is an augmentation of IL-1 and IL-2 production by the antigen-presenting spleen cell population. However, neonatal spleen cells do not respond to the same levels as do adult spleen cells. The addition of exogenous IL-1 cannot repair the antigen presentation by neonatal cells. Experiments in which the antigen processing and presentation steps were separated from those requiring growth factor induction and secretion demonstrate that neonatal spleen cells are impaired in their ability to perform adequate antigen processing and presentation. The neonatal spleen cells are as competent as adult cells to cooperate with T-helper cells and secrete growth factors, provided antigen processing and presentation is performed by fully competent adult spleen cells. Experiments in which neonatal and adult antigen-presenting spleen cell populations were mixed, and others in which plastic adherent and nonadherent cells were separated, could not detect any suppressor mechanisms responsible for the low antigen presentation of neonatal cells. Thus, neonatal spleen cells are impaired in the initial stages of antigen processing and presentation. This impairment which leads to low levels of growth factor production is the major determinant in the ineffectual stimulation of T-helper cells by neonatal spleen cells.

Delta-9-tetrahydrocannabinol inhibits macrophage protein expression in response to bacterial immunomodulators

The objective of this study was to determine the effect of delta-9-tetrahydrocannabinol (delta-9-THC), the major psychoactive component of marihuana, on macrophage protein expression in response to bacterial immunomodulators. Peritoneal macrophages of (B6C3)F1 mice receiving Propionibacterium acnes exhibited a novel protein profile when compared to resident or vehicle-treated macrophages. In contrast, macrophages from mice treated with P. acnes in concert with delta-9-THC exhibited profiles for which the majority of protein species reverted to patterns seen in profiles of resident or vehicle-treated macrophages. Treatment of the murine macrophage line P388D1 (DBA/2) in vitro with bacterial lipopolysaccharide (LPS) resulted in the hyperproduction of a subset of proteins ranging from 73 to 18 kD relative molecular weight. Coexposure of the P388D1 cells to LPS and 10(-7) M to 10(-5) M delta-9-THC resulted in a dose-related depletion of these proteins. These results suggest that delta-9-THC suppresses the expression of proteins elicited by macrophage bacterial immunomodulators.

Regulation of constitutive and lymphokine-induced Ia expression by murine alpha-fetoprotein

alpha-Fetoprotein (AFP) has been shown to suppress a variety of immune responses in vitro. The immunosuppressive properties of AFP can be partly attributed to the ability of this protein to decrease the cell surface expression of Ia antigens on macrophages. The experiments described in this report define more precisely the regulatory effects of AFP on Ia expression. Using the "dendritic-like" cell line P388 AD2 and bone marrow-derived macrophages we have shown that AFP can suppress the constitutive expression of cell surface Ia antigens. This decrease is detectable on the cell surface 24 hr after the addition of AFP. In further experiments we also examined the effect of AFP on lymphokine-induced Ia expression. Our results show that AFP has no suppressive influence on the inductive phase of lymphokine-induced Ia antigen expression but can decrease elevated levels of Ia antigen subsequent to their induction.

Isolation and characterization of Hofbauer cells from human placental villi

Hofbauer cells are a major cell type of the human placental villous core and they are particularly numerous at the beginning of pregnancy. In the present study we describe a method suitable to obtain HC suspensions in a highly purified form. These suspensions have been analyzed for surface markers using a battery of monoclonal antibodies. Of all the surface markers used, Hofbauer cells were only positive for 4F2, LeuM2 and LeuM3 monoclonals which mainly detect cells of the monocyte-macrophage lineage. Hofbauer cells were consistently negative for HLA-DR antigens, C3bR and T- or B-cell markers. Hofbauer cells appeared capable of phagocytosing latex beads, adhering to and spreading over plastic surface and secreting lysozyme. In contrast, they failed to originate an efficient respiratory burst in response to appropriate stimulation. Hofbauer cells were positive for ANAE with a perinuclear localization of the enzyme activity, but consistently negative for peroxidase. These observations suggest that they share a number of features with cells of the monocyte-macrophage lineage and yet have some distinctive properties.

IFN-induced modulation of histocompatibility antigens on human cells. Background, mechanisms and perspectives

IFN proteins are a family of lymphokines with anti-viral effects. Several other effects of IFNs have also been described, including enhancement of natural killer (NK) cell activity, enhancement of cytotoxic T-lymphocyte activity, and enhancement of the expression of major histocompatibility complex (MHC) antigens. The latter effects have been characterized as immunomodulatory, whereas the well-known inhibition of growth of malignant cells has been termed anti-proliferative. This review summarizes the current knowledge of the enhancement of MHC products by IFNs. Whereas the basic methodologies for demonstrating the enhancement are simple and reliable, especially when using flow cytometry (FCM), the biological relevance of this reaction is largely unknown. Based on recent findings, however, we have hypothesized that the above-mentioned diverse effects of IFNs are all - in some way or other - related to the classical anti-viral mechanism. This concept proposes that the MHC-enhancing effect of IFNs is a vital part of the immunological defense against virus infections and an integral part of the anti-viral effects of IFN proteins.

Neuraminidase-treated macrophages stimulate allogenic CD8+ T cells in the presence of exogenous interleukin 2

Prior work has shown that purified, resident, and inflammatory peritoneal macrophages are weak stimulators of the allogeneic MLR. We have identified conditions whereby thioglycollate-elicited macrophages become stimulatory, but primarily for the CD8+ T cell subset. The conditions were to treat the macrophages with neuraminidase and to supplement the MLR with rIL-2. These treatments together led to proliferative and cytotoxic responses by isolated CD8+ but not CD4+ T cells. Likewise when MHC-congenic strains were evaluated, an MLR was observed across isolated class I but not class II MHC barriers. Pretreatment of the macrophages with IFN-gamma further enhanced expression of class I MHC products and stimulatory activity, but did not seem essential. While these treatments did not render macrophages stimulatory for an MLR in purified CD4+ cells, blastogenesis of CD4+ cells was observed when the MLR involved bulk T cells. Small allogeneic B lymphocytes behaved similarly to macrophages, in the pretreatment with neuraminidase and supplementation with rIL-2 rendered B cells stimulatory for allogeneic, enriched, CD8+, but not CD4+, T cells. Spleen adherent cells, which are mixtures of macrophages and dendritic cells, stimulated both CD4+ and CD8+ T cells, and neither neuraminidase nor exogenous IL-2 was required. We think that these data suggest that most macrophages and small B cells lack three important functions of dendritic cells: a T cell-binding function that can be remedied by neuraminidase treatment, a T cell growth factor-inducing function that can be bypassed with exogenous IL-2, and an IL-2 responsiveness function that is required by CD4+ lymphocytes.

Cytokines amplify the function of accessory cells

Accessory cells have two broad functions at the onset of T cell-mediated immunity. One is the "presentation" of antigen in association with MHC products. The other is a "sensitization" function which is thought to require IL-1 and leads to the development of lymphoblasts that secrete lymphokines and respond to T cell growth factors. This review summarizes evidence, much of it recent, that specific cytokines upregulate both the presentation and sensitization functions of accessory cells. Lymphokines, particularly IFN-gamma, upregulate class II MHC products on macrophages and many non-leukocytes, but not dendritic cells. The enhanced levels of class II improve presentation to T lymphoblasts, but not the sensitization of unprimed and memory T cells. Dendritic cells in lymph and lymphoid organs are active accessory cells for primary responses without any supplementation by exogenous cytokines. IL-1, while not a product of dendritic cells, further amplifies their function several fold. In thymus, IL-1 has a second effect, including the formation of Ia+ thymic dendritic cells from Ia- precursors. Granulocyte-macrophage colony stimulating factor (GM-CSF) is an important cytokine for epidermal Langerhans cells, which are immature dendritic cells. GM-CSF maintains viability in culture, and enhances the sensitization function for primary responses 10-20 fold. Why does the immune system regulate expression of Ia on many cell types, as well as dendritic cell function? In the discussion, it is proposed that the local modification of accessory cells by cytokines helps to reduce anti-self or autoreactive T cell responses, and to enhance the retention of sensitized T cells at sites of antigen deposition.

Serological characterization of macrophage hybridomas: identification of an interferon-gamma-inducible surface marker

Macrophage hybridoma clones prepared by fusion of splenic adherent cells with P388D1 tumor cells have previously been shown to be heterogeneous with respect to function at the clonal level. In this study the macrophage clones were phenotypically characterized by indirect RIA using a battery of rat MAbs to murine myeloid and lymphoid cell surface markers. All macrophage clones expressed the common leukocyte antigen T200 and the Mac-1 alpha and beta chains. Markers which were differentially expressed among the clones included class II antigens and the antigens detected by MAbs MIV 55, MIV 38, and 14G8. The antigens detected by the latter three MAbs were referred to as MBR-1, -2 and -3, respectively. Functional heterogeneity did not correlate with phenotypic heterogeneity among the macrophage clones. Treatment of macrophage clones with IFN-gamma resulted in a significant increase in the expression of class II antigens and induced the expression of MBR antigens on some clones which were constitutively negative for these markers. The clonal distribution and induction patterns of class II antigen as compared to MBR antigen indicated that regulation of expression of these markers was independent. In addition, the clonal distribution and induction pattern of MBR antigens, along with competitive binding studies using radiolabeled MIV 38 and 14G8 MAbs, suggested that the three MBR antigens were similar or closely associated molecules.

Quantitation of surface antigens on cultured murine epidermal Langerhans cells: rapid and selective increase in the level of surface MHC products

It was recently discovered that murine epidermal Langerhans cells (LC) changed significantly in function and phenotype when maintained in culture. Notably, accessory cell function for primary immune responses increased while cytologic markers like ATPase, nonspecific esterase, and Birbeck granules were lost. To further analyze LC differentiation, we used flow cytometry and a panel of 22 monoclonal antibodies to quantitate changes in surface antigens at the single-cell level. A striking change was a fivefold increase in the amount of Ia antigens (which are expressed on class II MHC products) during the first day of culture. The increase was evident within 3 h and reached a plateau at 15-24 h. Both I-A and I-E products behaved similarly. The increase in Ia was blocked by 1 microgram/ml cycloheximide. Expression of other surface antigens was then monitored on Ia+ LC by two-color flow cytometry. Low levels of class I (H-2D and H-2K) MHC products were detected on freshly isolated LC, and these antigens also increased severalfold during the first day of culture. Fc receptors (identified with the 2.4G2 mAb) and the F4/80 macrophage antigen decreased, as reported previously. Three antigens that were detected in fresh suspensions were expressed at constant levels in culture. These were the C3bi receptor and the pan leukocyte and interdigitating cell antigens. Several leukocyte antigens that were not found initially on LCs did not appear, including B220 anti-B cell, 33D1 anti-dendritic cell, and CD4, CD5, CD8 T-cell specificities. We conclude that the surface of cultured LCs undergoes selective changes in culture. As a result, the cells are rich in Ia and H-2 and have detectable C3bi receptors, but have little or no LFA-1, Ti, CD4, 5, and 8, 33D1, 2.4G2, F4/80, and B220 antigens.

Immunohistological analysis of experimental gingivitis in humans

Immunohistological analysis of experimental gingivitis in humans was carried out to provide a baseline for the study of immunoregulatory mechanisms in chronic inflammatory periodontal disease. Using a panel of monoclonal antibodies in an avidin biotin immunoperoxidase technique, T cell subsets were identified and the pattern of Class II major histocompatibility complex (MHC) antigens determined. Twenty third-year dental students took part in the study. Following the cessation of oral hygiene procedures, gingival biopsies were taken from each of five students at days 0, 4, 8 and 21 during the development of the inflammatory lesion. Each student had one biopsy which healed uneventfully. The T4:T8 ratio showed only slight variation over the time course of the lesion varying from 2.18:1 at day 0 to 2.48:1 at day 4. At all stages the T cells displayed both HLA-DR and HLA-DQ antigens, but less than 10% had detectable IL-2 receptors. The predominant macrophage population was acid phosphatase + ve, adenosine triphosphatase -ve, HLA-DR+ and HLA-DQ+ antigens suggesting an activated phagocytic population. During the development of the lesion, the number of intraepithelial Langerhans cells (T6+) increased but there appeared to be a discrepancy between HLA-DR and HLA-DQ expression on these cells. Similarly, the keratinocytes expressed HLA-DR but failed to express HLA-DQ at any stage. These results suggest that the developing gingival lesion is a well controlled lesion and follows a similar pattern to a controlled delayed type hypersensitivity (DTH) response.

Functional analysis of Ia antigen-bearing keratinocytes: mixed skin lymphocyte culture between Ia antigen-bearing Pam 212 cells and allogeneic and syngeneic splenic T cells

Keratinocytes express Ia antigens in various skin disorders, although the biological role of these Ia antigen-bearing (Ia+) keratinocytes remains unclear. We induced Ia antigens on Pam 212 murine keratinocyte cell line by interferon-gamma(IFN-gamma) and using these cells, we performed the mixed skin lymphocyte culture with syngeneic BALB/c or allogeneic C3H/He splenic T cells. Unexpectedly, Pam 212 cells were found to stimulate both syngeneic and allogeneic T cells irrespective of IFN-gamma treatment. However, both syngeneic and allogeneic T cells cultured with IFN-gamma-treated Pam 212 cells incorporated [3H]thymidine much more actively than those cultured with IFN-gamma-untreated Pam 212 cells. This stimulation was not inhibited by monoclonal anti-I-Ad antibody. Analysis of the responding T cells demonstrated that the syngeneic T-cell stimulation by IFN-gamma-treated Pam 212 cells occurred in both purified Lyt 1-T cells and Lyt 2- T cells. Furthermore, we found that the T cells cultured with the IFN-gamma-treated cells were composed of two morphologically different types of cells. Determination of their surface phenotype showed that the small cell population consisted of 57% Thy-1+, 23% Lyt-1+, 6% Lyt-2+, and 9% asialo-GM1+ cells, while the large cells consisted of 53% Thy-1+, 15% Lyt-1+, 9% Lyt-2+, and 24% asialo-GM1+ cells. These findings suggest that IFN-gamma-treated Pam 212 cells could stimulate more than one kind of splenic T cell populations.

Synthesis and expression of MHC class II molecules in the absence of attached invariant chains by recombinant-interferon-gamma-activated bone-marrow-derived macrophages

Pure populations of in vitro propagated bone marrow-derived macrophages are constitutively Ia negative. Co-culturing of these cells with recombinant interferon-gamma (rIFN-gamma) resulted in the appearance of high amounts of Ia antigens at the cell surface of essentially all cells. The continuous presence of the stimulus was a prerequisite for sustained Ia expression because removal of the stimulus resulted in rapid decline of surface Ia. Two-dimensional (2D) gel analysis (1D isoelectric focusing, 2D sodium dodecyl sulfate-polyacrylamide gel electrophoresis) of class II molecules synthesized by rIFN-gamma-stimulated bone marrow macrophages (BMM phi) revealed that, in contrast to class II complexes hitherto described, BMM phi-derived I-A and I-E subregion-encoded subunits are synthesized without invariant chains. The invariant chain-deficient alpha,beta heterodimers are expressed at the cell surface in high proportions demonstrating that their correct assembly and transport to the cell surface is accomplished in the absence of invariant chains. The lack of invariant chains appears not to be due to a failure of rIFN-gamma to induce transcription of the gamma-chain gene because rIFN-gamma-induced, in contrast to uninduced, BMM phi accumulate high levels of invariant chain-specific transcripts as evidenced by Northern blot analysis. These findings suggest that translation of gamma-chain-specific mRNA is blocked in BMM phi for as yet unknown reasons. Alternatively, newly synthesized gamma chains might have escaped their regular intracellular maturation pathway as a result of unidentified modifications mediated by altered post-translational processing mechanisms.

Gamma interferon-mediated increase in the number of Ia-bearing macrophages during infection with Listeria monocytogenes

The role of gamma interferon (IFN-gamma) in an increase in Ia-bearing macrophages during Listeria monocytogenes infection was studied. The peritoneal macrophages from L. monocytogenes-infected mice contained a high proportion of Ia. Intraperitoneal injection of the supernatant from a culture of spleen cells from L. monocytogenes-infected mice induced Ia-rich exudates in normal mice. The Ia-inducing activity in the culture supernatant was abrogated by the pretreatment of spleen cells with anti-Thy-1.2 antibody plus complement. Immunoadsorption of the culture supernatant with anti-recombinant IFN-gamma antibody and protein A-Sepharose CL-4B completely abrogated its Ia-inducing activity. These results suggested that an increase in Ia-bearing macrophages during L. monocytogenes infection was attributable to T-cell-derived IFN-gamma.

Selective activation of helper and cytolytic T-cell functions of L3T4+ clones with either antireceptor antibody or phorbol ester and ionophore

After activation with specific antigen and antigen presenting cells (APC) L3T4+ inducer T-cell clones can lyse Ia+ APC. The present study characterizes the mechanism of activation and specificity of L3T4+ inducer cell-mediated cytolytic function. Two methods that bypass the physiological stimulus of antigen presented on Ia+ APC were used to activate L3T4+ clones. The first method utilized an antireceptor monoclonal antibody (MAb), KJ16.133, to activate KJ16.133+ clones. The activated clones expressed nonspecific cytolytic activity, killing target cells irrespective of their H-2 haplotype or their ability to express cell surface Ia molecules. The crosslinking of bound KJ16.133 antibody greatly enhanced cytolytic activity. This activation is receptor specific because KJ16.133- clones were not activated under identical conditions. The second method of activation was provided by a synergistic action of phorbol-12-myristate-13-acetate (PMA) and ionophore A23187. These agents nonspecifically activated all L3T4+ clones tested. The simultaneous presence of the two agents is required for maximal activation. Again, the activated clones expressed potent nonspecific cytolytic activity. These observations demonstrated that L3T4+ inducer T-cell-mediated killing can be separated into two stages: an activation step, which can be specifically and nonspecifically triggered and an effector phase which causes nonspecific lysis of bystander targets. The induction of nonspecific cytolytic activity by antireceptor MAb was inhibited by anti-L3T4 MAb (GK1.5). In contrast, activation of nonspecific cytolytic activity by treatment with PMA plus A23187 was not inhibited by anti-L3T4 MAb. Under the above activation conditions, antireceptor MAb selectively induced the secretion of IL-3 and expression of nonspecific cytolytic activity. However, there was little or no concomitant proliferation and production of IL-2. In contrast, activation by PMA plus A23187 coordinately induces expression of nonspecific cytolytic activity, secretion of lymphokines (IL-3 and IL-2), and cell proliferation. Thus, the anticlonotypic activation preferentially induces certain functions whereas activation with PMA plus A23187 is not selective.

Cloned protein antigen-specific, Ia-restricted T cells with both helper and cytolytic activities: mechanisms of activation and killing

Myoglobin-specific, Iad-restricted cloned helper T cells and T hybridomas were found to directly kill Iad-bearing, myoglobin-pulsed B lymphoma targets and could also kill bystander targets, but only in the presence of antigen-pulsed antigen presenting cells (APC). The induction of the killing requires recognition of processed antigen in the context of class II major histocompatibility complex (MHC) molecules. Despite the specificity of induction, the bystander killing suggests a nonspecific lytic mechanism. The direct killing can be inhibited only by cold specific targets, whereas the bystander killing can be blocked by both specific and nonspecific targets. The cold target inhibition seems to be due to interference with effector-to-target contact or proximity rather than due to high-dose suppression of T-cell activation. Experiments using T-cell supernatants or cyclosporin A suggested that the helper T cells kill targets by synthesizing short-range soluble factor(s) with nonspecific killing activity de novo during the effector phase, but only while antigen-specific signal transduction is occurring. The mechanism of cold target inhibition appears to be absorption or consumption of a short-acting cytotoxic lymphokine by cells which must be able to interact closely with the effector cell. Normal spleen B cells, despite their capability for activating the helper T cells, cannot inhibit specific killing or be killed by helper T cells, even after lipopolysaccharide stimulation. Thus, although killing by helper T cells may play a negative feedback role in the normal immune response, our data raise the possibility that the helper T-cell-mediated killing may contribute to the immune surveillance against malignancy by virtue of the preferential killing of tumor cells either directly or indirectly.

Thymus-dependent and -independent regulation of Ia antigen expression in situ by cells in the synovium of rats with streptococcal cell wall-induced arthritis. Differences in site and intensity of expression in euthymic, athymic, and cyclosporin A-treated LEW and F344 rats

Euthymic LEW rats, when injected with streptococcal cell walls, exhibited rapid onset development of acute exudative arthritis coincident with enhanced synovial expression of Ia antigen. By 21 d after injection, the expression of Ia was markedly increased compared with basal conditions and paralleled the severity of the later developing proliferative and erosive disease. Immunodeficient athymic and cyclosporin A-treated LEW rats developed only the early phase arthritis, which was again paralleled by synovial Ia expression. Chronic expression of high levels of Ia antigen was not observed. Histocompatible F344 rats, both athymic and euthymic, developed minimal, if any, clinically significant arthritis and did not exhibit the enhanced Ia expression demonstrated in the LEW rats. Our results indicate that enhanced synovial Ia expression parallels clinical disease severity and varies by rat strain, and that the rapid onset enhanced synovial Ia expression is thymus independent, whereas the markedly enhanced chronic phase Ia expression is thymus dependent.

Definition of a differentiation antigen on the surface of phagocytic cells of thymic reticulum which is down-regulated by interferon gamma

Monoclonal antibodies (MoAb) were raised against phagocytic cells of thymic reticulum (P-TR) grown in vitro. Each of the two MoAb (TR-1N, TR-3N) defined two polypeptides of 46-57 kDa on P-TR membrane. TR-1N and TR-3N recognize respectively 48 and 81% of P-TR, but do not recognize any cells in spleen, lymph node, thymic lymphocytes, or bone marrow. They bind to part of peritoneal macrophages and to macrophage cell lines J 774 and P 388 D1. Cell binding of TR-1N and TR-3N was compared by immunofluorescence to that of anti-CR3 antibody (Mac-1) which recognizes P-TR, a small number of cells in bone marrow and spleen, and a much higher percentage of peritoneal macrophages. The polypeptides recognized by TR-1N/TR-3N may be defined as differentiation antigens on accessory cells as they appear on bone marrow cells during maturation in vitro in the presence of L-cell supernatant which contains colony stimulating factor (CSF-1). Interferon gamma is able to down-regulate the expression of TR-1N/TR-3N antigen on P-TR membrane while that of Mac-1 is unchanged and that of Ia is up-regulated.

Ia antigen expression and IL-1 activity in murine tumour-associated macrophages

Tumour-associated macrophages (TAM) isolated from five murine sarcomas had a relatively high frequency of I-A+ cells, with mean values of 27% (mFS6), 52% (MN/MCA1), 68% (N3), 62% (N4) and 98% (J3) for TAM compared to 12% for resident peritoneal macrophages. Expression of I-E in TAM was also high (29%) in the only sarcoma (N4) examined in this respect. Expression of I-A by TAM declined in culture but exposure to lymphokine supernatants maintained and increased the frequency of I-A+ cells in TAM. Transplantation of tumours into nude mice caused a marked decrease in the percentage of I-A+ TAM in the case of the N4 sarcoma (8% compared to 48%), whereas for the MN/MCA1 sarcoma the diminution was only marginal (from 53 to 41%), TAM from murine sarcomas did not constitutively release appreciable levels of interleukin-1 (IL-1) activity. Upon stimulation with bacterial lipopolysaccharides or silica, TAM showed a limited capacity to produce and release IL-1 activity compared to peritoneal macrophages. Thus the expression of I-A antigens and the IL-1-producing capacity are uncoupled in TAM from murine sarcomas. These properties of TAM could play an important role in the generation of anti-tumour immunity and/or of suppressive T-cell circuits.

Virus-induced immunosuppression

Infection with a variety of viruses results in the suppression of the host's immune system. Several mechanisms thought to be responsible for this effect are discussed: infection and alteration of lymphocytes and macrophages, production of soluble suppressor factors, and the induction of suppressor cells. The clinical significance of virus-induced immunosuppression is also discussed.

Induction of HLA-DR antigen expression in human endometrial epithelial cells in vitro by recombinant gamma-interferon

Recent studies suggest that HLA-DR antigens may be inducible in some normal epithelial cells. Therefore, we studied the expression of these molecules in epithelial cell cultures derived from 9 proliferative and 7 secretory endometria with and without treatment by recombinant gamma-interferon (gamma-IFN). A panel of monoclonal antibodies to HLA-DR antigens, T cells, B cells, macrophages, endothelial cells, and cytokeratin was used to stain the cultured cells by the avidin-biotin complex method. The cultures consisted only of epithelial cells as demonstrated by expression of cytokeratin and by electron microscopy and did not contain any T or B cells, macrophages, or endothelial cells. The endometrial epithelial cells were HLA-DR-negative under routine culture conditions but expressed HLA-DR antigens after gamma-IFN treatment in a dose- and time-dependent fashion. The findings indicate that endometrial epithelium can actively synthesize HLA-DR antigens in vitro after induction by gamma-IFN.

Phylogeny of lymphocyte heterogeneity: the cellular requirements for the mixed leucocyte reaction with channel catfish

Vigorous mixed leucocyte reactions (MLR) were obtained using channel catfish peripheral blood leucocytes (PBL) when equal numbers of responder and stimulator cells (5 X 10(5) cells each) were cocultured. The use of 2000 rads of X-irradiation was sufficient to block subsequent proliferative responses of the stimulator cells. The cellular requirements for channel catfish MLR responses were assessed by using three functionally distinct leucocyte subpopulations isolated from the PBL. B cells (sIg+ lymphocytes) and T cells (sIg- lymphocytes) were isolated by an indirect panning procedure employing a monoclonal antibody specific for channel catfish Ig. A third population, monocytes, was isolated or depleted by adherence to baby hamster kidney cell microexudate-coated surfaces or adherence to Sephadex G-10, respectively. The results indicated that only the T cells were able to respond in the fish MLR, with monocytes being required as accessory cells. In contrast, all three cell types could function as stimulator cells. In addition, it was observed that low in vitro culture temperatures inhibited the generation of channel catfish MLRs, thereby supporting the contention that low temperature immunosuppression in fish results from a preferential inhibition of the generation of primary T-cell responses.

Modulation of class II (DR and DQ) antigen expression on gingival Langerhans cells in vitro by gamma interferon and prostaglandin E2

The effect of human and murine gamma interferon (IFN-gamma) on Class II (DR and DQ) expression by human gingival Langerhans cells (LC) was examined using an organ culture system. Human and murine IFN-gamma increased the expression of both DR and DQ antigens during a 72-h period. Maximal levels of DR expression (100% of T6+ cells) were produced within 6 h of IFN-gamma treatment and were maintained during culture. DQ expression was maximal (100% of T6+ cells) at 18 h and was more labile than DR. The effect of IFN-gamma on DR and DQ was abrogated by prostaglandin E2 (PGE) while indomethacin, and inhibitor of PGE synthesis, mimicked the effect of IFN-gamma on DR and DQ expression. Gingival keratinocytes maintained their expression of DR for 72 h in the presence of gamma-IFN, but did not express DQ under any of the culture conditions used in this study. These results demonstrate that gamma-IFN induces differential expression of Class II antigens in the oral mucosa in vitro, and suggest that gamma-IFN and PGE may be involved in the control of DR and DQ antigen expression in vivo.

Supernatants of human leukocytes contain mediator, different from interferon gamma, which induces expression of MHC class II antigens

In this report, data are presented on the regulation of MHC class II antigen expression by a mediator present in supernatants of human mixed leukocyte cultures (MLC-SN), and which is different from IFN-gamma. The capacity of supernatants to induce antigen expression did not correspond to titers of IFN-gamma. Removal of IFN-gamma using either dialysis against pH 2 or neutralizing mAb against human IFN-gamma did not abrogate the MHC class II antigen expression-inducing capacity of MLC-SN when tested on adenocarcinoma cell lines, kidney epithelial cells, and fibroblasts in vitro in an indirect immunofluorescence assay. Therefore, supernatants of human leukocytes contain a mediator, different from IFN-gamma, which induces expression of MHC class II antigens. Dose-response studies revealed that the mediator is produced after allogeneic and lectin stimulation of human leukocytes, and by unstimulated leukocytes. Activation of leukocytes resulted in increased titers of the mediator. The mediator markedly enhances expression of both HLA-DR and HLA-DQ antigens, whereas IFN-gamma had a similar effect on HLA-DR antigens, and only a minor effect on HLA-DQ antigens. Interaction of the mediator and IFN-gamma resulted in a potentiating effect of these two factors on MHC class II antigen expression. Biochemical analysis revealed a mediator, distinguishable by FPLC from IL-1, IL-2, and human IFN-gamma, and which has a molecular mass of 32 kD.

In vitro granuloma formation using defined antigenic nidi

The in vitro granuloma model provides an excellent tool to study granulomatous hypersensitivity. In our studies of granuloma formation in schistosomiasis, we have demonstrated the utility of the model with respect to analysis of human PBL responses, cloned T cells, purified antigens of the parasite, and regulatory mechanisms. We have also presented data which demonstrate the applicability of this model to other antigenic systems. While the suggestion that this model may be suitable for the study of sarcoidosis may be premature, we would propose that the system may be adapted to screen potentially causative antigens. Furthermore, with the identification of the critical antigen(s), the in vitro granuloma model will facilitate studies at the clinical level.

Influence of delayed immune reactions on human epidermal keratinocytes

The epidermal changes that occur in human cutaneous immune responses have been investigated in the tuberculin reaction and in the lesions of tuberculoid and lepromatous leprosy and cutaneous leishmaniasis. In each situation, there was a dermal accumulation of monocytes and T cells, and the epidermis exhibited thickening. In the tuberculin response, the thickness of the epidermis sometimes doubled in 48-72 hr, and this was attributed to increases in both size and number of keratinocytes. In addition, the phenotype of the keratinocytes changed from Ia- to Ia+. Similar changes in keratinocyte Ia-antigen expression occurred in the epidermis overlying untreated tuberculoid leprosy and cutaneous leishmaniasis lesions, but not in lepromatous leprosy. We suggest that one or more epidermal growth factors may be generated in the course of a delayed immune reaction in the dermis.

Control of Ia antigen expression on phagocytic cells of the thymic reticulum by interferon-gamma and prostaglandins

Phagocytic cells of the thymic reticulum (P-TR) spawned in the microenvironment of primary thymic stroma cultures express class II antigens on their membranes. We can show that Ia-antigen expression is regulated by the local secretion of interferon-gamma (IFN-gamma): (a) early primary culture supernatants contain IFN as tested by a cytopathogenic inhibition test after concentration of IFN activity; (b) the addition of a specific anti-IFN-gamma antiserum to primary cultures reduces Ia expression on P-TR suggesting that IFN-gamma produced in situ is implicated in Ia expression; (c) the percentage of Ia+ cells declines as primary cultures age. This phenomenon parallels the disappearance of thymocytes which are the supposed candidate for IFN-gamma secretion. (d) When isolated from their stromal environment and replated in secondary cultures, P-TR lose their membrane Ia antigen which can be re-expressed in the presence of recombinant IFN-gamma, but not IFN-alpha/beta. The decline of Ia expression on P-TR during the aging of primary cultures may be delayed by the inhibition of prostaglandin secretion.