The regulatory role of macrophages in antigenic stimulation. Part Two: symbiotic relationship between lymphocytes and macrophages

Engineering Escherichia coli-Derived Nanoparticles for Vaccine Development

The development of effective vaccines necessitates a delicate balance between maximizing immunogenicity and minimizing safety concerns. Subunit vaccines, while generally considered safe, often fail to elicit robust and durable immune responses. Nanotechnology presents a promising approach to address this dilemma, enabling subunit antigens to mimic critical aspects of native pathogens, such as nanoscale dimensions, geometry, and highly repetitive antigen display. Various expression systems, including Escherichia coli (E. coli), yeast, baculovirus/insect cells, and Chinese hamster ovary (CHO) cells, have been explored for the production of nanoparticle vaccines. Among these, E. coli stands out due to its cost-effectiveness, scalability, rapid production cycle, and high yields. However, the E. coli manufacturing platform faces challenges related to its unfavorable redox environment for disulfide bond formation, lack of post-translational modifications, and difficulties in achieving proper protein folding. This review focuses on molecular and protein engineering strategies to enhance protein solubility in E. coli and facilitate the in vitro reassembly of virus-like particles (VLPs). We also discuss approaches for antigen display on nanocarrier surfaces and methods to stabilize these carriers. These bioengineering approaches, in combination with advanced nanocarrier design, hold significant potential for developing highly effective and affordable E. coli-derived nanovaccines, paving the way for improved protection against a wide range of infectious diseases.

Oil-in-ionic liquid nanoemulsion-based adjuvant simultaneously enhances the stability and immune responses of inactivated foot-and-mouth disease virus

Maintaining structural integrity and enhancing stability of inactivated foot-and-mouth disease virus (iFMDV) antigen in adjuvants is crucial to ensure the vaccine potency. Unfortunately, formulation with most reported adjuvants leads to the accelerated dissociation of iFMDV into inactive pentamers. Here, an ionic liquid, i.e., choline and niacin ([Cho][Nic]), which was found to stabilize iFMDV against the acid- and thermo- induced dissociation in buffer solution, was applied to construct a novel oil-in-ionic liquid (o/IL) nanoemulsion adjuvant composed of [Cho][Nic], squalene, and Tween 80. The o/IL nanoemulsion formulated with iFMDV has a monodisperse diameter of 135.8 ± 40.4 nm. The thermostability and long-term stability of iFMDV were remarkably enhanced in o/IL nanoemulsion compared with that in the o/w emulsion without [Cho][Nic] and in the commercial Montanide ISA 206 adjuvant. The o/IL nanoemulsion exerted its adjuvant effects by improving the humoral immune responses. Immunization of o/IL nanoemulsion adjuvanted iFMDV induced specific IgG titers similar to that adjuvanted by Montanide ISA 206 and about 4-fold higher than the un-adjuvanted iFMDV, also promoted the activation of B lymphocytes and the secretion of interleukin-4 in the mice model. This [Cho][Nic]-based o/IL nanoemulsion can serve as a promising adjuvant platform for the foot-and-mouth disease vaccine.

Genetic and pharmacological validation of TAK1 inhibition in macrophages as a therapeutic strategy to effectively inhibit TNF secretion

Immune challenge of invading macrophages at sites of infection is associated with release of TNF, which triggers a local cytokine storm as part of the normal inflammatory response. Whereas this response maybe beneficial in fighting off infections, similar responses triggered in autoimmune diseases contribute significantly to the underlying damaging pathology associated with these diseases. Here we show that Takinib, a highly discriminatory inhibitor of transforming growth factor Beta- activated kinase 1 (TAK1), selectively and potently reduces TNF production in pro-inflammatory THP-1 macrophages. A complete survey of 110 cytokines, showed robust loss of proinflammatory cytokine responsiveness to lipopolysaccharide (LPS) and interferon gamma (IFNγ) challenge in response to Takinib. The mechanisms of action of Takinib was recapitulated in TAK1 KO macrophages. TAK1 KO cells showed significant loss of TNF production as well as release of IL-6 in response to LPS challenge. Furthermore, Takinib blocked the ability of exogenously added LPS to promote phosphorylation of, c-Jun, p38 protein kinases as well as downstream transcription factors regulated by nuclear factor κ-light-chain-enhancer of activated B cells (NFκB). In a mouse LPS challenge model, Takinib significantly reduced TNF serum levels. Our findings demonstrate that Takinib has utility in the treatment inflammatory disease by locally suppressing TNF production from invading macrophages.

Desert Dust and Health: A Central Asian Review and Steppe Case Study

In Asian deserts environmental and anthropomorphic dust is a significant health risk to rural populations. Natural sources in dry landscapes are exacerbated by human activities that increase the vulnerability to dust and dust-borne disease vectors. Today in Central and Inner Asian drylands, agriculture, mining, and rapid development contribute to dust generation and community exposure. Thorough review of limited dust investigation in the region implies but does not quantify health risks. Anthropogenic sources, such as the drying of the Aral Sea, highlight the shifting dust dynamics across the Central EurAsian steppe. In the Gobi Desert, our case study in Khanbogd, Mongolia addressed large-scale mining’s potential dust risk to the health of the local population. Dust traps showed variable exposure to particulates among herder households and town residents; dust density distribution indicated that sources beyond the mine need to be considered when identifying particulate sources. Research suggests that atmospheric dust from multiple causes may enhance human particulate exposure. Greater awareness of dust in greater Central Asia reflects community concern about related health implications. Future human well-being in the region will require more thorough information on dust emissions in the changing environment.

Extremely low-frequency electromagnetic field exposure enhances inflammatory response and inhibits effect of antioxidant in RAW 264.7 cells

In recent years, there has been a dramatic increase in the number and variety of electronic devices that emit electromagnetic waves. Because people live and work in close proximity to these pieces of electrical equipment, there is growing concern surrounding the destruction of homeostasis by electromagnetic field exposure. In the present study, the effects of 60 Hz 0.8 mT extremely low-frequency electromagnetic fields (ELF-EMF) on a macrophage cell line (RAW 264.7) were examined. Under defined ELF-EMF exposure conditions, the production of nitric oxide and pro-inflammatory cytokines, TNF-α, IL-1β, and IL-6, were increased in RAW 264.7 cells and the expression of those genes was also upregulated. However, cell proliferation was not altered. Translocation of NF-κB (nuclear factor kappa B), molecules that act downstream of the pro-inflammatory cytokines, were increased to the nucleus under ELF-EMF exposure conditions. In addition, we found that ELF-EMF exposure elevated activation of nuclear factor of activated T cells (NFAT) 2, as well as positively affected the influx of calcium. Furthermore, with both the presence of a potent antioxidant (Resveratrol) and downregulation of the antioxidant-related gene Prx-1 (Peroxiredoxin-1), ELF-EMF was associated with higher inflammatory responses of macrophages. These results suggest that an ELF-EMF amplifies inflammatory responses through enhanced macrophage activation and can decrease the effectiveness of antioxidants. Bioelectromagnetics. 38:374-385, 2017. © 2017 Wiley Periodicals, Inc.

The Bidirectional Relationship between Sleep and Immunity against Infections

Sleep is considered an important modulator of the immune response. Thus, a lack of sleep can weaken immunity, increasing organism susceptibility to infection. For instance, shorter sleep durations are associated with a rise in suffering from the common cold. The function of sleep in altering immune responses must be determined to understand how sleep deprivation increases the susceptibility to viral, bacterial, and parasitic infections. There are several explanations for greater susceptibility to infections after reduced sleep, such as impaired mitogenic proliferation of lymphocytes, decreased HLA-DR expression, the upregulation of CD14+, and variations in CD4+ and CD8+ T lymphocytes, which have been observed during partial sleep deprivation. Also, steroid hormones, in addition to regulating sexual behavior, influence sleep. Thus, we hypothesize that sleep and the immune-endocrine system have a bidirectional relationship in governing various physiological processes, including immunity to infections. This review discusses the evidence on the bidirectional effects of the immune response against viral, bacterial, and parasitic infections on sleep patterns and how the lack of sleep affects the immune response against such agents. Because sleep is essential in the maintenance of homeostasis, these situations must be adapted to elicit changes in sleep patterns and other physiological parameters during the immune response to infections to which the organism is continuously exposed.

Antigen processing and presentation to T cells

In this article Howard Grey and Robert Chesnut describe recent insights into the mechanism of antigen presentation and discuss the needfor antigen processing in the stimulation of T cells.

The phagocytes of neonate rat primary mixed glial cultures

The phagocytes present in mechanically dissociated neonate rat cerebral hemispheres have been cultured and characterized both qualitatively and quantitatively. They comprise about 10% of the starting cell suspension and persist but do not proliferate in culture. They do not possess neuronal or neuroglial antigens but do express the leukocyte common antigen and readily ingest both latex beads and opsonized erythrocytes. the latter by an Fc receptor-mediated process. Evidence is presented that these cells are a bona fida component of the neonate central nervous system.

Effect of the potent antiviral 1-cinnamoyl-3,11-dihydroxymeliacarpin on cytokine production by murine macrophages stimulated with HSV-2

The limonoid 1-cinnamoyl-3,11-dihydroxymeliacarpin (CDM) isolated from leaf extracts of Melia azedarach L, has potent antiherpetic effect in epithelial cells. Since Meliacine, the partially purified extract source of CDM, has therapeutic effect on murine genital herpes, the potential use of CDM as microbicide against herpetic infections was studied here. To determine the cytotoxic effect of CDM, the MTT assay and acridine orange staining of living cells were performed. The antiherpetic action of CDM was measured by plaque reduction assay, and the immunomodulatory effect was determined by measuring the cytokine production using a bioassay and ELISA method. The results presented here showed that CDM inhibited Herpes Simplex Virus type 2 (HSV-2) multiplication in Vero cells but did not affect its replication in macrophages which were not permissive to HSV infection. In macrophages, levels of TNF-α, IFN-γ, NO, IL-6 and IL-10 were increased by CDM used alone or in combination with HSV-2. Besides, CDM not only synergized TNF-α production combined with IFN-γ, but also prolonged its expression in time. Results indicate that CDM inhibits HSV-2 multiplication in epithelial cells and also increases cytokine production in macrophages, both important actions to the clearance of infecting virus in the mouse vagina.

Opportunities and challenges of the pulmonary route for vaccination

INTRODUCTION

The respiratory tract is an attractive target for the delivery of vaccine antigens. Potential advantages of drug delivery by means of the pulmonary route include accessibility, non-invasiveness, ease of administration, and the possibility to reach an elaborate mucosal network of antigen-presenting cells.

AREAS COVERED

This review discusses current pulmonary vaccination strategies and their advantages and disadvantages.

EXPERT OPINION

To improve efficiency of vaccination and develop new strategies, a well-founded knowledge about composition and characterization of antigen-presenting cell populations throughout the respiratory tract is essential. In particular, respiratory tract dendritic cells, as key antigen-presenting cells in the lung, constitute an ideal target for vaccine delivery. Furthermore, particle size is a key factor when designing new inhalable vaccines, as size determines not only deposition in different respiratory tract compartments, but also how an antigen and its carrier will interact with lung tissue components and immune cells. An increased knowledge of different respiratory tract antigen-presenting cell populations and their interactions with other components of the immune system will enable new targeting strategies to improve the efficacy of pulmonary vaccination.

Modulating temporal control of NF-kappaB activation: implications for therapeutic and assay selection

The activation of transcription factor NF-kappaB (nuclear factor-kappaB) plays a central role in the induction of many inflammatory response genes. This process is characterized by either oscillations or stable induction of NF-kappaB nuclear binding. Changes in dynamics of binding result in the expression of distinct subsets of genes leading to different physiological outcomes. We examined NF-kappaB DNA binding activity in lipopolysaccharide (LPS)-stimulated IC-21 cells by electromobility shift assay and nonradioactive transcription factor assay and interpreted the results using a kinetic model of NF-kappaB activation. Both assays detected damped oscillatory behavior of NF-kappaB with differences in sensitivity and reproducibility. 3,4-Dichloropropionaniline (DCPA) was used to modulate the oscillatory behavior of NF-kappaB after LPS stimulation. DCPA is known to inhibit the production of two NF-kappaB-inducible cytokines, IL-6 and tumor necrosis factor alpha, by reducing but not completely abrogating NF-kappaB-induced transcription. DCPA treatment resulted in a potentiation of early LPS-induced NF-kappaB activation. The nonradioactive transcription factor assay, which has a higher signal/noise ratio than the electromobility shift assay, combined with in silico modeling, produced results that revealed changes in NF-kappaB dynamics which, to the best of our knowledge, have never been previously reported. These results highlight the importance of cell type and stimulus specificity in transcription factor activity assessment. In addition, assay selection has important implications for network inference and drug discovery.

Regulation of in vivo immune responses: few principles and much ignorance

An attempt is made, based largely on reports of experiments carried out in vitro, to piece together the sequence of events between the interaction of antigens with B or T lymphocytes and the immune responses which result. These include stimulation of B lymphocytes to secrete antibody or to become B memory cells, and stimulation of T helper cells and cytotoxic/suppressor T cells to multiply and become functional effector cells. Thymus-independent (T1) stimulation is described of a subpopulation of B cells by poorly degradable immunogens with multiple epitopes, and the generation of B memory cells, as well as stimulation of B cells requiring cooperation with T cells. Stimulation of T helper (TH) cells by antigens involves first activation by interleukin 1 (IL-1) and then presentation of the antigen at the surface of antigen-presenting cells (usually macrophages, dendritic cells or B cells) in association with class II major histocompatibility complex molecules (MHC II); for extrinsic (foreign) proteins this requires initial capture of the protein, followed by denaturation and/or degradation so as to associate the molecule or fragments with MHC II. Some peptides can become suitably associated without further degradation, whereas T1 antigens may be unable to become associated effectively. T cells so stimulated express receptors for interleukin 2 (IL-2), and secrete various molecules, including factors which stimulate B cells to divide and/or secrete Ig, interferon-gamma and IL-2. In turn, IL-2 causes proliferation of TH and cytotoxic/suppressor T cells. Interferon-gamma stimulates the expression of MHC II by macrophages and some epithelial cells and increases the activity of NK (natural killer) cells. This simplified account embraces many of the experimental observations, but there are sufficient exceptions to make clear that much remains to be discovered even in respect of the interactions of antigen-presenting cells, T cells and B cells in vitro. Application of such general principles to predict the outcome of immunization in vivo would need also to take into account the microenvironments in lymphoid tissues where antigens are retained, and the flow of lymphocytes through them; how long the antigens persist; and how the immune response is modified by responses already elicited, including the idiotype network. Because such information is not usually available, enlightened guess-work may still be the best guide to practice.

Macrophages as stimulators of MART-1 27-35 epitope-specific human cytolytic T lymphocytes in vitro

BACKGROUND

Activation and expansion of antigen-specific cytolytic T lymphocytes (CTL) require epitope presented by antigen-presenting cells (APC). Presently, dendritic cells (DC) are viewed as the most efficient APC. Since the recognition of DCs as the professional APC, the paradigm has emerged that macrophage (MPhi) are scavengers and are incapable of activating T cells.

METHOD

The melanoma-associated MART-1(27-35) peptide-loaded MPhi from HLA-A2-positive donors were used to activate MART-1(27-35) epitope-specific CTL in vitro.

RESULTS

We show that peptide-pulsed MPhi stimulate MART-1(27-35) epitope-specific precursors to proliferate and to express effector functions. We also show that upon restimulation with the peptide pulsed MPhi, a fraction of the epitope-specific CTLs undergoes activation-induced cell death. The activation-induced cell death is induced in an epitope-specific manner and through apoptosis.

CONCLUSION

MPhi can function as APC and are also capable of modulating expansion and contraction of CTL response in vitro.

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.

Production of interferon-gamma by myeloid cells--fact or fancy?

Myeloid cells are usually viewed as targets rather than producers of interferon (IFN)-gamma. However, since 1993 several studies have suggested that macrophages and dendritic cells can also secrete IFN-gamma in response to various stimuli, which led to the idea of autocrine myeloid-cell activation in innate immunity. Here, we review this concept in the light of recent findings that illustrate the necessity of specific cell markers, cell purity, sensitive single-cell cytokine detection methods, and of further insights into the developmental origin of myeloid and lymphoid cell lineages. We also discuss the possible function of intracellular IFN-gamma in macrophages and the evidence for a protective role of myeloid IFN-gamma in vivo.

Monocytes with altered phenotypes in posttrauma patients

CONTEXT

Posttrauma patients show impaired immune responsiveness and increased susceptibility to infections. Although monocytes in these patients have been known to express decreased HLA-DR, induction of HLA-DR using interferon gamma failed to reduce susceptibility to infection, suggesting additional factors also may be involved in the impaired immune responsiveness. CD4 plays an integral role in most of the functions of HLA-DR. In newborn infants, who have impaired immune responsiveness, we found a concomitant reduction of CD4 on monocytes with decreased HLA-DR expression.

OBJECTIVE

Because monocytes in posttrauma patients have not been previously studied for morphology, coexpression of CD4 and HLA-DR, and activity of alpha-naphthyl butyrate esterase, the purpose of this study was to analyze these factors in this population.

DESIGN

Monocyte morphology; expression of CD4, CD11b, CD13, CD16, and HLA-DR by 3-color flow cytometry; and analysis of alpha-naphthyl butyrate esterase activity by cytochemical staining were studied in 27 posttrauma patients and 20 control subjects.

RESULTS

Monocytes in posttrauma patients showed significant differences in the following characteristics compared with controls: (1) increase of subsets displaying the phenotypes CD4-/CD14+/HLA-DR- and CD4-/CD14+/CD16-, (2) decrease in mean fluorescence intensity of CD4 and HLA-DR expression in monocytes that were positive for these markers, (3) decrease in alpha-naphthyl butyrate esterase activity, and (4) decreased amount of cytoplasm and cytoplasmic vacuoles.Conclusion.-Our study suggests that in posttrauma patients, as in newborns, there is a marked increase of monocytes with decreased expression of CD4 and HLA-DR, as well as decreased alpha-naphthyl butyrate esterase activity. Concomitant reduction in CD4 and HLA-DR expression on monocytes may contribute to impaired immune responsiveness in these patients.

Perspective on antigen processing and presentation

The phenomenon of antigen processing and presentation and the concept that T cells recognize peptides resulting from the partial catabolism of proteins, are relatively new. These concepts were first recognized and developed at a time when lymphocyte immunity - the adaptive system - and cellular immunity, with its major component of activated macrophages, were not perceived as part of one integrated system. To me, it was the fundamental findings on the role of major histocompatibility (MHC) molecules that set the framework for understanding how phagocytes and the antigen presenting cell (APC) system interact with the adaptive cellular system, in a truly symbiotic relationship (1). In this chapter we make a historical review of the developments that, in my biased opinion, led to the understanding of antigen presentation as a central event. I emphasize my own work, placing it in my perspective of how I saw the field moving.

Hu 210: a potent tool for investigations of the cannabinoid system

The synthetic compound HU 210 displays a multiplicity of biochemical, pharmacological, and behavioral effects, most of which have been demonstrated to be dependent on a selective agonistic activity at CB(1) and CB(2) cannabinoid receptors and to involve the main neurotransmitter systems. Results obtained in various studies suggest a potential clinical application of this highly potent drug (e.g., as antipyretic, antiinflammatory, analgesic, antiemetic, and antipsychotic agent) as well as its usefulness in research aimed to develop a better understanding of the involvement of the endogenous cannabinoid system in a number of physiopathological functions.

Peptide binding and antigen presentation by class II histocompatibility glycoproteins

The immune system has evolved complex mechanisms for the recognition and elimination of pathogens. CD4+ helper T lymphocytes play a central role in orchestrating immune responses and their activation is carefully regulated. These cells selectively recognize short peptide antigens stably associated with membrane-bound class II histocompatibility glycoproteins that are selectively expressed in specialized antigen presenting cells. The class II-peptide complexes are generated through a series of events that occur in membrane-bound compartments within antigen presenting cells that, collectively, have become known as the class II antigen processing pathway. In the present paper, our current understanding of this pathway is reviewed with emphasis on mechanisms that regulate peptide binding by class II histocompatibility molecules.

Macrophage suppression of T cell activation: a potential mechanism of peripheral tolerance

The mechanisms of induction and maintenance of tolerance in self-reactive T cells in the periphery are poorly understood. Current models assume that successful T cell activation only occurs if ligation of the T cell receptor (signal 1) by antigen presenting cells (APCs) is accompanied by a costimulatory signal (signal 2), and that signal 1 in the absence of signal 2 is either ignored or is tolerizing. However, there is also evidence for the existence of macrophages (M phi) capable of suppressing T cell activation both in vitro and in vivo. The possibility of a more actively induced tolerance exists, in which the M phi itself responds to T cell-mediated signals in a tolerogenic fashion. This would help to resolve the paradox that tissue M phi, which act as scavengers of self-antigen, can also act as professional APCs. The ability of tissue macrophages to actively suppress T cells would further underscore the importance of the innate immune system in regulating adaptive immune responses.

Calcineurin and vacuolar-type H+-ATPase modulate macrophage effector functions

While effector molecules produced by activated macrophages (including nitric oxide, tumor necrosis factor alpha, interleukin 1, etc.) help to eliminate pathogens, high levels of these molecules can be deleterious to the host itself. Despite their importance, the mechanisms modulating macrophage effector functions are poorly understood. This work introduces two key negative regulators that control the levels and duration of macrophage cytokine production. Vacuolar-type H+-ATPase (V-ATPase) and calcineurin (Cn) constitutively act in normal macrophages to suppress expression of inflammatory cytokines in the absence of specific activation and to inhibit macrophage cytokine responses induced by bacterial lipopolysaccharide (V-ATPase), interferon gamma (V-ATPase and Cn), and calcium (Ca2+) flux (Cn). Cn and V-ATPase modulate effector gene expression at the mRNA level by inhibiting transcription factor NF-kappaB. This negative regulation by Cn is opposite to its crucial positive role in T cells, where it activates NFAT transcription factor(s) leading to expression of interleukin 2, tumor necrosis factor alpha, and other cytokine genes. The negative effects of V-ATPase and Cn on NF-kappaB-dependent gene expression are not limited to the macrophage lineage, as similar effects have been seen with a murine fibroblast cell line and with primary astrocytes.

Lymphocytes and dendritic cells in the normal uterine cervix. An immunohistochemical study

OBJECTIVE

Assessment of the appearance, distribution and numerical density of immune cell populations in the normal human uterine cervix.

STUDY DESIGN

SETTING

University Hospital Gasthuisberg.

SUBJECTS

29 healthy women undergoing total hysterectomy for non-cervical benign uterine disease.

ANALYSIS

Immunohistochemistry and morphometrical analysis on histological sections containing ectocervix, transformation zone and endocervix, using antibodies against the following antigens: HLA-DR, CD4, CD22, CD1a and CD8.

STATISTICAL ANALYSIS

Wilcoxon rank sum test.

RESULTS

Lymphocytes in the epithelial and stromal compartments are predominantly T-lymphocytes. Intraepithelial T-lymphocyte and Langerhans' cell densities and their distribution are not influenced by the menstrual cycle and are the same in both ectocervix and transformation zone.

CONCLUSION

The wide variation of T lymphocyte subpopulations and Langerhans' cell densities in the normal epithelium of the uterine cervix is stressed. We are the first to present a large and well-defined control series, which is indispensable to study the effect of smoking and other factors on the cervical immune system.

The cellular immunology associated with autoimmune thrombocytopenic purpura: an update

Chronic autoimmune thrombocytopenic purpura (AITP) is an organ specific autoimmune bleeding disease in which autoantibodies are directed against the individual's own platelets, resulting in increased Fc-mediated platelet destruction by macrophages in the reticuloendothelial system. Although AITP is primarily mediated by IgG auto-antibodies, their production is regulated by the influence of T lymphocytes and antigen presenting cells (APC). This review argues that enhanced T helper cell/antigen presenting cell interactions in patients with AITP may be responsible for IgG anti-platelet auto-antibody production. Understanding these cellular immune responses in AITP may lead to the development of more immune specific therapies for the management of this disease.

Immunobiology of T helper cells and antigen-presenting cells in autoimmune thrombocytopenic purpura (ITP)

Autoimmune thrombocytopenic purpura (AITP) is a bleeding disease in which autoantibodies are directed against the individual's own platelets, resulting in enhanced Fc-mediated platelet destruction by macrophages in the reticuloendothelial system. Most research in AITP has focused on characterization of the autoantibodies, while little has been devoted to the cellular immune mechanisms leading to autoantibody production. This report summarizes the current state of the literature and argues that enhanced T helper cell/antigen-presenting cell interactions in patients with AITP are the primary stimulus for the development of antiplatelet autoantibody production. Understanding these events is important for eventually identifying disease-initiating platelet autoantigens and ultimately developing specific immunotherapies for AITP.

Studies in listeriosis show the strong symbiosis between the innate cellular system and the T-cell response

Resistance to infection with Listeria monocytogenes involves a series of cellular interactions, many of which are carried out by cytokines. Macrophages, NK cells and neutrophils participate in early stages of Listeria resistance. The neutrophil is specially important for clearance of the liver phase of listeriosis. Macrophages and NK cells interact by way of IL-12 and TNF, which induce the NK cell to produce IFN-gamma. IFN-gamma is the major macrophage-activating cytokine. The CB-17 SCID mouse shows these cellular interactions restricting the growth of Listeria, without its elimination. CD4 and/or CD8 T cells bring about sterilizing immunity. Macrophages influence the lymphocyte response by way of antigen presentation and also by promoting Th 1 differentiation. Thus, elimination of Listeria requires a symbiosis between innate immunity and the T-cell system.

Production of interleukin 1 from macrophages incubated with poly (DL-lactic acid) granules containing ovalbumin

The production profile of interleukin 1 (IL-1) from mouse peritoneal macrophages (M phi) was determined following their incubation with poly(DL-lactic acid) (PDLLA) granules containing ovalbumin (OVA). Upon incubation, M phi produced IL-1 at a significantly high rate compared with those incubated with OVA in the free form or OVA-free granules. A simple mixture of empty granules and free OVA exhibited the same level of IL-1 production as induced by free OVA alone. IL-1 production by the granules with a fixed OVA loading increased with an increase in their amount added to M phi. When incubated with a fixed amount of granules containing OVA of different loadings, M phi produced more IL-1 with an increase in the total OVA amount, but the IL-1 production decreased at OVA loadings higher than 10%. The presence of free OVA enhanced IL-1 production with the increased addition of empty granules, but the level induced by OVA loaded in granules was higher than that by mixtures of free OVA and empty granules, when compared at a similar OVA dose, irrespective of the absolute amount of PDLLA added. These findings indicate that the sustained release of OVA from the granules is critical to enhance the OVA-induced IL-1 production, in contrast to the OVA release accompanying a large initial burst, which reduced IL-1 production. It was concluded that the direct contact of PDLLA granules with M phi and the subsequent sustained release of OVA around M phi effectively activated M phi, resulting in enhanced IL-1 production.

Reversible impairment in monocyte major histocompatibility complex class II expression in malnourished surgical patients

BACKGROUND

Upregulation of major histocompatibility complex (MHC) class II antigen in response to the T-cell lymphokine interferon-gamma (IFN-gamma) is central to T cell-macrophage cooperation and immune homeostasis. We evaluated this property in malnourished surgical patients and assessed the impact of nutrition repletion with total parenteral nutrition (TPN).

METHODS

Sixty-two patients were studied: 37 malnourished and 25 controls. Whole blood was cultured with or without IFN-gamma (100 U mL-1), dual-labeled with anti-CD14 (monocyte) and anti-human leukocyte antigen-DR antibodies and analyzed by flow cytometry. Phagocytosis was measured by flow cytometry. In a second study, 10 severely malnourished patients received 5 days of TPN and MHC class II expression was measured at the end of this period.

RESULTS

The magnitude of the increase in monocyte MHC class II expression in response to IFN-gamma was significantly increased in the control group compared with the malnourished group (107% vs 53%; p < .05). This impairment directly correlated with severity of malnutrition, but did not correlate with age or disease type. The number of bacteria phagocytozed per cell was significantly decreased (p < .05) in the malnourished group. In study 2, there was a significant increase in MHC class II induction with IFN-gamma after short-term TPN (58% before vs 173% after, p < .001).

CONCLUSIONS

MHC class II induction in response to IFN-gamma is significantly impaired in malnourished patients, correlating with the severity of malnutrition. This defect is reversed by short-term TPN. These data identify the reversible loss of a key mechanism, fundamental to host defense, that may enhance the risk of infection in malnourished patients.

Enumeration and characterization of memory cells in the TH compartment

There is a great deal of interest in understanding how helper T cells differentiate in vivo and exert their regulatory role on a developing, immune response. Essential to development of protective immunity is the development of memory T cells. To study memory T cells in vivo we first need the means to identify and characterize these cells as they develop in their complex microenvironments. We have developed a method which allows us to directly purify both primary and memory helper T cells from the draining lymph nodes of mice as they respond to pigeon cytochrome c in vivo. Junctional sequences from these populations and from individual T cells show a strong selection for CDR3 length and residues characteristic of antigen binding. Overall these studies support a model of progressive clonal maturation with the memory T cell repertoire being more homogeneous than that of the primary response. There is some suggestion that affinity maturation may take place after repeated immunization, but on a more modest scale than that seen for antibodies. Finally we present the use of two new technologies that promise to greatly expand the analysis of immune responses in vivo. The use of flow cytometry with simultaneous detection of five and six fluorescence parameters helps to reliably resolve rare subsets of antigen-specific cells in order to understand the progression of their differentiation in vivo. Lastly, we have developed peptide/MHC tetramers as a new class of staining reagent that has wide applicability in the study of T cell responses in vivo.

An immunohistochemical study of topical cyclosporine in vernal keratoconjunctivitis

PURPOSE

To determine the immunomodulating effects of topical cyclosporine on the immune cells in the conjunctival biopsy specimens obtained from patients with active vernal keratoconjunctivitis.

METHODS

We studied six patients who had severe active vernal keratoconjunctivitis. Each patient was given topical cyclosporine 2% eyedrops four times daily. A 2 x 2-mm limbal conjunctival biopsy specimen was obtained from each patient before and three weeks after treatment. Using a panel of monoclonal and polyclonal antibodies and immunohistochemical techniques, we analyzed the conjunctival immune cells before and after cyclosporine treatment.

RESULTS

Three weeks after topical cyclosporine treatment, there was marked clinical improvement and a statistically significant reduction in the number of epithelial and stromal class II MHC+ cells, UCHL1+ T cells, and stromal IgA+ and IgG+ plasma cells. The mean number of cells before and after therapy, respectively, were: class II MHC+ (epithelium), 31.5 +/- 13.1 and 8.3 +/- 5.6 (P = .031); class II MHC+ (stroma), 77.0 +/- 28.7 and 24.7 +/- 17.5 (P = .031); UCHL1+ T cells (epithelium), 24.5 +/- 14.1 and 4.2 +/- 2.9 (P = .031); UCHL1+ T cells (stroma), 78.7 +/- 31.1 and 44.5 +/- 27.5 (P = .031); IgA+ plasma cells, 66.7 +/- 32.1 and 22.2 +/- 7.8 (P = .031); and IgG+ plasma cells, 37.3 +/- 30.0 and 9.0 +/- 6.4 (P = .031). There was a statistically insignificant decrease in the epithelial class II MHC+ dendritic Langerhans cells, epithelial and stromal KP1+ macrophages, stromal OPD4+ helper/inducer T cells, and stromal L26+ B cells. The numbers of IgE+ plasma cells and mast cells were unaltered.

CONCLUSION

The clinical improvement in vernal keratoconjunctivitis after topical cyclosporine therapy may result from its immunomodulating effect on the components of cell-mediated and humoral immune responses. In contrast, the drug has no immunomodulatory effect on mast cells and IgE-mediated allergic response.

In vitro response of lymphocytes from bronchoalveolar lavage fluid and peripheral blood to mitogen stimulation during natural maedi-visna virus infection

To investigate the effects of maedi-visna virus (MVV) infection on cell-mediated immunity, the in vitro response of bronchoalveolar lavage fluid (BALF) and peripheral blood (BP) lymphocytes (PBL) to exogenous mitogen was analysed. BALF and PBL from control (n = 9) and MVV-infected (n = 7) animals were cultured fro 3 days in the presence and absence of concanavalin A (Con A). Lymphocyte expression of the interleukin-2 receptor (IL-2R) antigen, a parameter of lymphocyte activation, was quantified by dual-colour flow cytometry using the bovine anti-IL-2R monoclonal antibody IL-A111. IL-2R expression by lymphocytes in BALF and PB from control and MVV-infected animals, with and without Con A stimulation, were compared. In the absence of Con A stimulation, the proportion of cultured BALF CD8+ and gamma delta T cells expressing IL-2R was significantly (P < 0.05) lower for MVV-infected animals than for controls. After Con A stimulation the proportion of BALF CD4+ lymphocytes from MVV-infected animals that expressed IL-2R remained significantly (P < 0.05) lower than for controls. Comparisons within group showed that, after Con A stimulation, the proportion of all the T cell subsets in the control group expressing IL-2R, namely CD4+ (P < 0.001), CD8+ (P < 0.001) and gamma delta T cells (P < 0.05), was significantly increased. In the MVV-infected group, this increase was significant (P < 0.05) for CD4+ and CD8+ T cells, but not for gamma delta T cells. In vitro mitogen stimulation of PB T lymphocytes from both control and MVV-infected animals induced a significant elevation in the proportion of all T cell subsets expressing IL-2R when compared to cultured unstimulated control cells. However, there was considerable heterogeneity in the response to Con A of PB T cells from both groups of animals. The expression of IL-2R followed a different pattern to that of BALF lymphocytes, the proportion of unstimulated gamma delta / IL-2R+ T cells from MVV-infected animals being significantly (P < 0.05) higher than that of controls, and the proportion of cultured unstimulated CD8+ / IL-2R+ T cells from MVV-infected animals being significantly (P < 0.05) lower than that from controls. From these studies it can be concluded that the BALF T lymphocyte immune dysfunction observed during natural MVV infection, characterized by impaired IL-2R expression, is maintained under in vitro conditions.

Ruthenium Red potently inhibits immune responses both in vitro and in vivo

Targeted drug screening revealed a compound, Ruthenium Red, which potently blocked proliferation of human T-cells. This compound is not generally cytotoxic or cytostatic, as judged by its lack of effect on the proliferation of a panel of transformed cell lines, but it exhibits true immunosuppressive properties. Ruthenium Red inhibits the T-cell proliferative response (with an IC50 approximately 100 nM) to a wide variety of agents, including viral antigens from herpes simplex virus, tetanus toxoid, alloantigens and IL-2. This compound did not alter the growth of an M-CSF-dependent cell line (M-NFS-60) in response to added growth factor. Time course studies revealed that Ruthenium Red could be added as late as 24 h after the initiation of T-cell stimulation by antigen and still produce maximal inhibition, indicating that later stages of signaling events are being effected. Ruthenium REd was then tested for its ability to abrogate immune response in vivo. It was discovered that this compound dramatically reduced the expansion of lymphocytes in draining lymph nodes of mice immunized with cytochrome c in adjuvants. Furthermore, Ruthenium Red also suppressed specific antibody production in mice following challenge with this antigen. The functional properties of Ruthenium Red have been compared with other immunosuppressive agents and reveal that this compound is most similar to rapamycin in its overall profile. The chemical structure of Ruthenium Red is quite different from these other agents; therefore, it may be extremely useful in helping dissect the activation pathway of T-cells. It will be important to explore further the therapeutic potential of this unique compound.

Antigen expression of alveolar macrophages in smokers and patients with lung diseases

Alveolar macrophage function was studied immunocytochemically using three monoclonal antibodies--macrophage CD 68 KP 1 (M), protein CD 11C (P), and anti-elastin (EL)--and three polyclonal antibodies--lysozyme (LZ), alpha-1-antitrypsin (AAT), and alpha-1-antichymotrypsin (AACT). The material for study was smears obtained from bronchial washings from 15 healthy persons and 60 patients with respiratory infections or primary or secondary malignant lung infiltration. Eight of the healthy group and 40 of the patient group were smokers (SM). The percentage of cells obtained from the washings which were macrophages was also measured. The intensity of staining reactions for each of the six antigens was noted and in general more intense staining was noted in smokers than in non-smokers. More intense staining was observed in patients with pulmonary infections (group II PI) and metastatic pulmonary infiltrations (group IV MP Ca) than in controls (group IC), while patients with primary lung cancer (group III PP Ca) had highly reduced staining reactions. The number of macrophages was similarly increased in all groups in comparison with the IC group for non-smokers and in all groups except III PP Ca for smokers. It is concluded that smoking, pulmonary infections, and metastatic infiltration of the lung are associated with an increase in the number and activity of alveolar macrophages, while patients with primary lung cancer have an increase in the number of macrophages which are functionally incompetent.

Up-regulation of surface antigens on epiplexus cells in postnatal rats following intraperitoneal injections of lipopolysaccharide

Epiplexus cells in postnatal rats exhibited a remarkable up-regulation of major histocompatibility complex class I and II antigen expression after intraperitoneal administration of bacterial lipopolysaccharide; other surface antigens, i.e. complement type 3 receptors and leukocyte common antigens, were also vigorously elevated when compared with those of the corresponding control rats. The immunostaining of epiplexus cells with OX-42, OX-18 and OX-1 for the detection of complement type 3 receptors, major histocompatibility class I and leukocyte common antigens, respectively, was noticeably enhanced with a drastic increase in their numbers. The most significant finding was the upsurge of OX-6-positive epiplexus cells exhibiting major histocompatibility class II antigens, especially in rats receiving two intraperitoneal injections of lipopolysaccharide and killed at the age of 14 days. Immunoelectron microscopy confirmed the above findings and added the fact that the immunoreactive site was confined to the plasma membrane. An interesting feature was the occurrence of OX-6-positive macrophage-like cells in transit across the choroid epithelium. It is concluded from this study that the upsurge of immunopositive epiplexus cells after lipopolysaccharide injections was partly attributed to the infiltration of stromal macrophages which migrated across the epithelium. The up-regulation of major histocompatibility complex class I and II antigen expression on epiplexus cells by lipopolysaccharide would enable them to carry out self-recognizing and antigen-presenting function in the ventricular system.

Monitoring canine lung allograft rejection using Ia antigen expression by bronchoalveolar lymphocytes

The expression of Ia antigens by lymphocytes in bronchoalveolar lavage (BAL) was evaluated after canine lung allotransplantation with immunosuppression using FK-506. The expression of Ia antigens labeled using an OKIa-1 monoclonal antibody from Ortho Diagnostic Systems was measured by flow cytometry. Twenty-three adult mongrel dogs underwent left lung allotransplantation and were treated with FK-506 at a dose of 0.1 mg/kg/day intramuscularly until death. Allograft rejection was evaluated microscopically. The percentage of OKIa-1-positive cells among the BAL lymphocytes was 34.8% +/- 8.9% (mean +/- SD) from the allografted lungs showing no rejection, whereas it was 68.8% +/- 16.2% from the allografted lungs which showed rejection (P < 0.01). When a diagnosis of rejection was made prior to pathologic examination by an OKIa-1-positive lymphocyte percentage of 42% or more, the sensitivity, specificity, and accuracy of diagnosis were 100%, 87.5%, and 94.1%, respectively. Subsequently, pulse steroid therapy was attempted in those dogs with a high rate of OKIa-1-positive lymphocytes in the BAL. In 3 of 4 dogs showing histological signs of rejection, a decrease in the rate of OKIa-1-positive cells among the BAL lymphocytes corresponded to an improvement in pathologic diagnosis. In two dogs with bacterial pneumonia and pulmonary vein thrombosis, densities indistinguishable from those of rejection were seen on chest roentgenograms, but in these dogs the rate of OKIa-1-positive BAL lymphocytes was 42% or less. In conclusion, Ia antigen expression by BAL lymphocytes could be useful for monitoring rejection in lung allotransplantation.

Gamma interferon induces rapid and coordinate activation of mitogen-activated protein kinase (extracellular signal-regulated kinase) and calcium-independent protein kinase C in human monocytes

Gamma interferon plays an important role in regulating the functional properties of mononuclear phagocytes. In the present study, the role of activated protein kinases in the mechanism of action of gamma interferon cell signaling in human peripheral blood monocytes was investigated. Analysis in vitro of 100,000 x g cytosolic fractions from untreated and interferon-treated cells showed that agonist treatment resulted in time- and concentration-dependent increases in phosphotransferase activity when myelin basic protein (MBP) was used as the substrate. Anion-exchange chromatography of high-speed supernatants prepared from detergent extracts of interferon-treated cells revealed two discrete peaks of MBP phosphotransferase activity. Immunoblotting of fractions from these peaks with antiphosphotyrosine antibodies and with antibodies that specifically recognize the family of mitogen-activated protein (MAP) kinases detected a MAP kinase with a subunit M(r) of 42,000 in the earliest-eluting peak (peak 1). Phosphorylation of the 42,000-M(r) protein on tyrosine was observed only after treatment of cells with interferon. The contribution of MAP kinase to the interferon-stimulated activity in peak 1 was confirmed by quantitative immunoprecipitation with anti-MAP kinase and antiphosphotyrosine antibodies. The conclusion that the interferon-activated MBP kinase in peak 1 could be accounted for by an activated MAP kinase was also supported by the finding that fractions from Mono Q peak 1 demonstrated activity towards a MAP kinase-specific substrate. The later-eluting peak of interferon-activated MBP phosphotransferase activity appeared to be accounted for by an activated protein kinase C (PKC). This conclusion is based upon analyses of immunoblotting and immunoprecipitation experiments with antibodies to PKC and was also supported by the observed inhibition of this kinase with a PKC pseudosubstrate peptide. The interferon-stimulated PKC present in Mono Q peak 2 was active in the absence of calcium ions, suggesting that it is a calcium-independent isoform of PKC.

Murine epidermal Langerhans cells and splenic dendritic cells present tumor-associated antigens to primed T cells

We examined the ability of epidermal Langerhans cells and splenic dendritic cells to present tumor-associated antigens (Ag) to immune T cells. Methylcholanthrene (MCA)-induced subcutaneous fibrosarcomas derived from C57BL/6 mice were used as tumor models. Our data demonstrate that both murine Langerhans cells and splenic dendritic cells have the capacity to present tumor-associated Ag to primed T cells. We found that variously treated tumor preparations (irradiated viable tumor cells, irradiated frozen-stored tumor cells, mitomycin C-treated viable tumor cells, and snap freeze-thawed tumor cell lysates) can be utilized for tumor Ag-pulsing. Primed CD4+ T cells demonstrated in vitro specificity towards their respective tumors and did not cross-react to other syngeneic MCA-induced or non-MCA-induced tumors. The T cell proliferative response critically depended on the presence of immune CD4+ T cells. We discuss the implications of these findings for the adoptive immunotherapy of cancer using immune CD4+ 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.

Progressive impairment of monocytic function in HIV-1-infected human macrophage hybridomas

Using human macrophage hybridomas infected with HIV-1, we investigated monocyte function over a 5-week period after HIV-1 infection. Two clones, 63 and 30, were infected with HIV-1IIIB. Infection was documented by RT activity (15 x 10(6) cpm/ml), intracytoplasmic staining with an anti-p24 antibody, in situ hybridization with an HIV-1-specific riboprobe, and electron microscopy showing intracytoplasmic virus. Two weeks after infection, clones 63 and 30 lost expression of all class II antigens (DR, 81.7 vs. 0%; DQ, 15.6 vs. 0%; and DP, 76.9 vs. 0%) while retaining expression of class I (87.4 vs. 84.1%), LFA-1 (82.4 vs. 83.1%), and LFA-3 (79.1 vs. 74.7%) antigens when compared to uninfected cells. When tested for functional integrity, infected but not uninfected clone 63 cells failed to stimulate a tetanus-specific MHC-restricted T cell proliferative response 2 weeks after infection. Cytokine secretion and antigen processing were also perturbed as production of IL-1 was abolished 2 weeks after infection (although IL-6 secretion was augmented) and infected clone 63 cells failed to process exogenous antigen. Last, the viability of T cells cocultured with infected clone 63 was dramatically decreased 35 days after infection (85 vs. 15%). There was no evidence of transmission of HIV-1 to T cells, suggesting a toxic effect of infected clone 63. Taken together, these data suggest that altered macrophage function in our system occurs at multiple levels, which may account for the early immunological defects described in HIV-1 infection.

Enhancement by monocytes of perforin production and its gene expression by human CD8+ T cells stimulated with interleukin-2

Pore‐forming protein (PFP) is an important effector molecule for cytotoxicity mediated by cytotoxic T cells and NK cells. In the present study, the effect of monocytes on PFP production by inter‐leukin‐2 (IL‐2)‐stimulated T lymphocytes was examined. Highly purified lymphocytes (>99%) and monocytes (> 90%) were isolated by centrifugal elutriation from peripheral blood of healthy donors, and, CD4+ and CD8+ cells were isolated from the purified lymphocytes by using antibody‐bound magnetic beads. PFP production was quantitated with a universal microspectrophotometer in combination with immunostaining using anti‐PFP antibody. Monocytes did not produce any PFP. High levels of PFP production were observed in CD8+ cells, but not CD4+ cells after incubation for 4 days with IL‐2. Addition of monocytes to cultures of CD8 + cells resulted in significant augmentation of PFP production after 3 days’ stimulation with IL‐2. Monokines (TNFα and IL‐6) caused a significant increase in PFP production by IL‐2‐stimulated CD8+ cells. Northern blot analysis revealed that the PFP mRNA level was enhanced by stimulation with IL‐2, and that addition of monocytes to cultures of CD8 + cells plus IL‐2 augmented their PFP mRNA expression. These observations suggest that monocytes are important in in situ regulation of the CD8 + T cell‐mediated cytotoxic response through production of PFP.

Induction of mouse monocyte Ia expression by a mesangial cell-derived product

Previous studies in many laboratories have shown that macrophage Ia expression is not constitutive but under regulation. We provide data which demonstrate that product(s) of mouse mesangial cell cultures induce blood monocyte Ia expression as demonstrated by immunofluorescence. This process is time-related and is also dependent on novel protein synthesis, being abrogated when the monocytes are pretreated with cycloheximide. Preliminary characterization shows the mesangial cell product to be sensitive to heating at 100 degrees C x 30 min, to be resistant to digestion by trypsin at a concentration of 4 x 10(-6) M, and to have a molecular size of 10-100 kD as established by Amicon ultrafiltration. The substance is not interferon-gamma (IFN-gamma) since cultured mesangial cells had no contaminating T cells, mesangial cell supernatant had no detectable levels of IFN-gamma, and the Ia-inducing activity of the mesangial cell product was not abrogated by incubation of monocytes with mesangial cell supernatant which had been immunoprecipitated with anti-IFN-gamma. Similarly, experiments using anti-CSF-1 have excluded the possibility that the substance is CSF-1. The results of the study have relevance to the mechanisms by which monocytes which take up residence in the glomerular mesangium acquire Ia positivity, and also provide a potentially novel pathway by which a tissue product may induce monocytes to express Ia.