Differential CD4+ and CD8+ T cell recognition of mycobacteria antigens in pediatric versus adult TB

T cells from young children may be limited in capacity to mount pro-inflammatory responses to intracellular pathogens, thus contributing to vulnerability to TB disease. We compared CD4+ and CD8+ T cell cytokine production in response to mycobacterial antigens and mitogen SEB, between Ugandan children <5 yr (PedTB) and adults (ATB) with culture-confirmed pulmonary TB. HIV-uninfected children (n=12) and adults (n=41) had blood drawn for PBMC isolation prior to TB treatment. CD4+ and CD8+ T cell production of IFNγ, IL2, and TNFα in response to ESAT6/CFP10 (EC), ESXJ, PE12/13, PE3, PPE15, and PPE51 peptide pools, and SEB, were assessed by intracellular flow cytometry. Proportions and frequencies of CD4+ and CD8+ T cells producing cytokines were compared using Fisher’s Exact and Kruskal-Wallis tests, respectively, with adjusted p-values <0.05 significant. PedTB and ATB had equivalent CD4+ and CD8+ T cell production of IFNγ, IL2, and TNFα, including polyfunctional responses, to EC. T cell cytokine responses to ESXJ and PPE51 were equivalent; significant differences were noted in CD4+ T cell responses to PE3 and PPE15, and CD8+ T cell responses to PE12/13. Frequencies of CD4+ T cells producing IFNγ or IL2 in response to SEB were lower (p<0.0001) in PedTB versus ATB. Young children with PedTB exhibited adult-like capacity to generate Th-1 cytokines in response to EC, ESXJ, and PPE 51. Pediatric responses to PE3, PPE15, and PE12/13 were impaired, suggesting that the breath of antigen recognition differs between infants and adults with TB. Differential T cell recognition of mycobacterial antigens between adults and children should be considered in development of novel T cell based diagnostics and vaccines targeting pediatric TB.

Supporting from grants by NIH: AI157807; HHSN272200900053C

The Missing Link in Correlates of Protective Tuberculosis Immunity: Recognizing the Infected Cell

For most vaccination studies, the assessment of vaccine-induced CD4+ and CD8+ T cells has relied upon the measurement of antigen-specific polyfunctional cells, typically using recombinant antigen or peptide pools. However, this approach leaves open the question as to whether or not these cells are responsive to the Mtb-infected cell within the context of Mtb infection and hence leaves open the possibility that a key parameter of vaccine immunogenicity may be overlooked. In this review, we discuss the case that these measurements almost certainly over-estimate the capacity of both CD4+ and CD8+ T cells to recognize the Mtb-infected cell.

Transcriptional profile of CD8+Vα7.2+CD161+ MAITs reveals distinct gene expression compared to CD8 memory T cells

Here, we applied a cell population transcriptomics strategy to sorted human memory CD8 T cells to define novel immune signatures of latent tuberculosis infection (LTBI) and understand the phenotype of tuberculosis (TB)-specific T cells. We found a 41-gene signature that could discriminate between memory CD8 T cells from healthy LTBI subjects and noninfected controls. The gene signature was dominated by genes known to be associated with mucosal associated invariant T cells (MAITs) and reflected the lower frequency of MAITs observed in individuals with LTBI. There was no evidence for a conventional CD8 T cell specific signature between the two cohorts. We therefore investigated the MAITs in more detail in these cohorts. Phenotyping based on Vα7.2 and CD161 expression and MR1 tetramers revealed 2 distinct populations of CD8+Vα7.2+CD161+ T cells: MR1 tetramer-restricted and MR1 tetramer-unrestricted, both of which had a distinct gene expression profile compared to CD8 memory T cells. Transcriptomic analysis of LTBI vs. noninfected individuals did not reveal significant differences for MR1 tetramer-restricted cells. However, interestingly, gene expression of MR1 tetramer-unrestricted cells showed a very different profile with large inter-individual diversity and a TB-specific signature. This was further strengthened by a more diverse TCR-α and -β repertoire of MR1 tetramer-unrestricted cells as compared to MR1 tetramer-restricted. Thus, cell population transcriptomics revealed a dominant MAIT signature in CD8 memory T cells that upon detailed investigation provided novel insights into the phenotype of different MAIT populations implicated in tuberculosis.

Biomarkers of Tuberculosis Severity and Treatment Effect: A Directed Screen of 70 Host Markers in a Randomized Clinical Trial

More efficacious treatment regimens are needed for tuberculosis, however, drug development is impeded by a lack of reliable biomarkers of disease severity and of treatment effect. We conducted a directed screen of host biomarkers in participants enrolled in a tuberculosis clinical trial to address this need. Serum samples from 319 protocol-correct, culture-confirmed pulmonary tuberculosis patients treated under direct observation as part of an international, phase 2 trial were screened for 70 markers of infection, inflammation, and metabolism. Biomarker assays were specifically developed for this study and quantified using a novel, multiplexed electrochemiluminescence assay. We evaluated the association of biomarkers with baseline characteristics, as well as with detailed microbiologic data, using Bonferroni-adjusted, linear regression models. Across numerous analyses, seven proteins, SAA1, PCT, IL-1β, IL-6, CRP, PTX-3 and MMP-8, showed recurring strong associations with markers of baseline disease severity, smear grade and cavitation; were strongly modulated by tuberculosis treatment; and had responses that were greater for patients who culture-converted at 8weeks. With treatment, all proteins decreased, except for osteocalcin, MCP-1 and MCP-4, which significantly increased. Several previously reported putative tuberculosis-associated biomarkers (HOMX1, neopterin, and cathelicidin) were not significantly associated with treatment response. In conclusion, across a geographically diverse and large population of tuberculosis patients enrolled in a clinical trial, several previously reported putative biomarkers were not significantly associated with treatment response, however, seven proteins had recurring strong associations with baseline radiographic and microbiologic measures of disease severity, as well as with early treatment response, deserving additional study.

Tuberculosis immunology in children: diagnostic and therapeutic challenges and opportunities

Tuberculosis (TB) is one of the most important causes of infectious morbidity and mortality worldwide. Young children are more likely to develop severe disease from the causative agent Mycobacterium tuberculosis. These clinical observations likely reflect fundamental differences in the immune systems of young children and adults. Essential to effective TB immunity are functioning macrophages, dendritic cells, strong Th1-type T-cell immunity and a relative absence of Th2-type T-cell immunity. Critical differences between adults and children relevant to TB immunity include deficiencies in macrophage and dendritic cell function, deficiencies in the development of Th1-type T-cells in response to pathogens, and the propensity for infants and young children to develop Th2-type CD4+ T-cells in response to immunogens. In this article, knowledge about the requisite components of protective immunity, differences between the immune systems of children and adults relevant to pediatric tuberculosis, M. tuberculosis-specific T-cell immunity in children, and potential application to immunodiagnostics and vaccine development will be reviewed.

Rudimentary TCR signaling triggers default IL-10 secretion by human Th1 cells

Understanding the process of inducing T cell activation has been hampered by the complex interactions between APC and inflammatory Th1 cells. To dissociate Ag-specific signaling through the TCR from costimulatory signaling, rTCR ligands (RTL) containing the alpha1 and beta1 domains of HLA-DR2b (DRA*0101:DRB1*1501) covalently linked with either the myelin basic protein peptide 85-99 (RTL303) or CABL-b3a2 (RTL311) peptides were constructed to provide a minimal ligand for peptide-specific TCRs. When incubated with peptide-specific Th1 cell clones in the absence of APC or costimulatory molecules, only the cognate RTL induced partial activation through the TCR. This partial activation included rapid TCR zeta-chain phosphorylation, calcium mobilization, and reduced extracellular signal-related kinase activity, as well as IL-10 production, but not proliferation or other obvious phenotypic changes. On restimulation with APC/peptide, the RTL-pretreated Th1 clones had reduced proliferation and secreted less IFN-gamma; IL-10 production persisted. These findings reveal for the first time the rudimentary signaling pattern delivered by initial engagement of the external TCR interface, which is further supplemented by coactivation molecules. Activation with RTLs provides a novel strategy for generating autoantigen-specific bystander suppression useful for treatment of complex autoimmune diseases.

T-cell clones derived by CD3 stimulation from hepatitis C virus explanted liver tissue are not representative of dominant clones present in vivo

Liver tissue from hepatitis C virus (HCV)-related end-stage disease contains T-cell infiltrates. The goal of this study is to determine whether CD4 T-cell clones established in vitro using an antigen-independent technique from explanted liver tissue (n = 3) are representative of dominant clones present in vivo. T-cell receptor (TCR) use by intrahepatic CD4 T cells was assessed by spectratype analysis. Clones were established from single CD4 T cells by culturing in vitro with anti-CD3 and interleukin-2 (n > 25 per patient). TCR genes expressed by each clone were identified by sequencing. When identical clones were isolated, the original spectratype was analyzed further to determine whether the clone was a dominant T-cell expansion in vivo. Evidence for clonal expansions was found in all patients by spectratyping. T cells expressing the same TCRBV genes used for spectratyping were cloned in vitro. Duplicate clones expressing the same TCR genes were observed in 2 patients. Confirmation that clones established in vitro matched those present in vivo was obtained for 2 clones. Many dominant clones identified by spectratyping did not proliferate in vitro. Although spectratyping suggested the widespread accumulation of clonal expansions in HCV-related end-stage liver disease, clones established in vitro using anti-CD3 were poorly representative of dominant clones present in vivo. Although cloning with anti-CD3 has the advantage of generating T-cell clones not biased a priori toward a specific antigen, modified cloning strategies will need to be developed to expand those clones that appear dominant in end-stage organs.

Classically restricted human CD8+ T lymphocytes derived from Mycobacterium tuberculosis-infected cells: definition of antigenic specificity

Previous studies in murine and human models have suggested an important role for HLA Ia-restricted CD8(+) T cells in host defense to Mycobacterium tuberculosis (Mtb). Therefore, understanding the Ags presented via HLA-Ia will be important in understanding the host response to Mtb and in rational vaccine design. We have used monocyte-derived dendritic cells in a limiting dilution analysis to generate Mtb-specific CD8(+) T cells. Two HLA-Ia-restricted CD8(+) T cell clones derived by this method were selected for detailed analysis. One was HLA-B44 restricted, and the other was HLA-B14 restricted. Both were found to react with Mtb-infected, but not bacillus Calmette-Guérin-infected, targets. For both these clones, the Ag was identified as culture filtrate protein 10 (CFP10)/Mtb11, a 10.8-kDa protein not expressed by bacillus Calmette-Guérin. Both clones were inhibited by the anti-class I Ab and anti-HLA-B,C Abs. Using a panel of CFP10/Mtb11-derived 15-aa peptides overlapping by 11 aa, the region containing the epitopes for both clones has been defined. Minimal 10-aa epitopes were defined for both clones. CD8(+) effector cells specific for these two epitopes are present at high frequency in the circulating pool. Moreover, the CD8(+) T cell response to CFP10/Mtb11 can be largely accounted for by the two epitopes defined herein, suggesting that this is the immunodominant response for this purified protein derivative-positive donor. This study represents the first time CD8(+) T cells generated against Mtb-infected APC have been used to elucidate an Mtb-specific CD8(+) T cell Ag.

Mycobacterium tuberculosis-reactive CD8+ T lymphocytes: the relative contribution of classical versus nonclassical HLA restriction

Previous studies in mice and humans models have suggested an important role for CD8+ T cells in host defense to Mycobacterium tuberculosis (Mtb). In humans, CD8+ Mtb-reactive T cells have been described that are HLA-A2-, B52-, as well as CD1-restricted. Recently, we have described Mtb-specific CD8+ T cells that are neither HLA-A-, B-, or C- nor group 1 CD1-restricted. At present, little is known about the relative contribution of each of these restriction specificities to the overall CD8+ response to Mtb. An IFN-gamma enzyme-linked immunospot assay was used to determine the frequency of Mtb-reactive CD8+ T cells directly from PBMC. The effector cell frequency among five healthy purified protein derivative-positive subjects was 1/7,600 +/- 4,300 compared with 1/16,000 +/- 7,000 in six purified protein derivative-negative controls. To determine the frequencies of classically, CD1-, and nonclassically restricted cells, a limiting dilution analysis was performed. In one purified protein derivative-positive subject, 192 clones were generated using Mtb-infected dendritic cells (DC). Clones were assessed for reactivity against control autologous DC, Mtb-infected autologous DC, and HLA-mismatched CD1+ targets (DC), as well as HLA-mismatched CD1- targets (macrophages). Of the 96 Mtb-reactive CD8+ T cell clones, four (4%) were classically restricted and 92 (96%) were nonclassically restricted. CD1-restricted cells were not detected. Of the classically restricted cells, two were HLA-B44 restricted and one was HLA-B14 restricted. These results suggest that while classically restricted CD8+ lymphocytes can be detected, they comprise a relatively small component of the overall CD8+ T cell response to Mtb. Further definition of the nonclassical response may aid development of an effective vaccine against tuberculosis.

Expression cloning of an immunodominant family of Mycobacterium tuberculosis antigens using human CD4(+) T cells

Development of a subunit vaccine for Mycobacterium tuberculosis (Mtb) is likely to be dependent on the identification of T cell antigens that induce strong proliferation and interferon gamma production from healthy purified protein derivative (PPD)(+) donors. We have developed a sensitive and rapid technique for screening an Mtb genomic library expressed in Escherichia coli using Mtb-specific CD4(+) T cells. Using this technique, we identified a family of highly related Mtb antigens. The gene of one family member encodes a 9.9-kD antigen, termed Mtb9.9A. Recombinant Mtb9.9A protein, expressed and purified from E. coli, elicited strong T cell proliferation and IFN-gamma production by peripheral blood mononuclear cells from PPD(+) but not PPD(-) individuals. Southern blot analysis and examination of the Mtb genome sequence revealed a family of highly related genes. A T cell line from a PPD(+) donor that failed to react with recombinant Mtb9.9A recognized one of the other family members, Mtb9.9C. Synthetic peptides were used to map the T cell epitope recognized by this line, and revealed a single amino acid substitution in this region when compared with Mtb9.9A. The direct identification of antigens using T cells from immune donors will undoubtedly be critical for the development of vaccines to several intracellular pathogens.

Cytomegalovirus US2 destroys two components of the MHC class II pathway, preventing recognition by CD4+ T cells

Human cytomegalovirus (HCMV) is a ubiquitous herpesvirus that causes life-threatening disease in patients who are immunosuppressed for bone marrow or tissue transplantation or who have AIDS (ref. 1). HCMV establishes lifelong latent infections and, after periodic reactivation from latency, uses a panel of immune evasion proteins to survive and replicate in the face of robust, fully primed host immunity. Monocyte/macrophages are important host cells for HCMV, serving as a latent reservoir and as a means of dissemination throughout the body. Macrophages and other HCMV-permissive cells, such as endothelial and glial cells, can express MHC class II proteins and present antigens to CD4+ T lymphocytes. Here, we show that the HCMV protein US2 causes degradation of two essential proteins in the MHC class II antigen presentation pathway: HLA-DR-alpha and DM-alpha. This was unexpected, as US2 has been shown to cause degradation of MHC class I (refs. 5,6), which has only limited homology with class II proteins. Expression of US2 in cells reduced or abolished their ability to present antigen to CD4+ T lymphocytes. Thus, US2 may allow HCMV-infected macrophages to remain relatively 'invisible' to CD4+ T cells, a property that would be important after virus reactivation.

Molecular characterization and human T-cell responses to a member of a novel Mycobacterium tuberculosis mtb39 gene family

We have used expression screening of a genomic Mycobacterium tuberculosis library with tuberculosis (TB) patient sera to identify novel genes that may be used diagnostically or in the development of a TB vaccine. Using this strategy, we have cloned a novel gene, termed mtb39a, that encodes a 39-kDa protein. Molecular characterization revealed that mtb39a is a member of a family of three highly related genes that are conserved among strains of M. tuberculosis and Mycobacterium bovis BCG but not in other mycobacterial species tested. Immunoblot analysis demonstrated the presence of Mtb39A in M. tuberculosis lysate but not in culture filtrate proteins (CFP), indicating that it is not a secreted antigen. This conclusion is strengthened by the observation that a human T-cell clone specific for purified recombinant Mtb39A protein recognized autologous dendritic cells infected with TB or pulsed with purified protein derivative (PPD) but did not respond to M. tuberculosis CFP. Purified recombinant Mtb39A elicited strong T-cell proliferative and gamma interferon responses in peripheral blood mononuclear cells from 9 of 12 PPD-positive individuals tested, and overlapping peptides were used to identify a minimum of 10 distinct T-cell epitopes. Additionally, mice immunized with mtb39a DNA have shown increased protection from M. tuberculosis challenge, as indicated by a reduction of bacterial load. The human T-cell responses and initial animal studies provide support for further evaluation of this antigen as a possible component of a subunit vaccine for M.tuberculosis.

Characterization of human CD8+ T cells reactive with Mycobacterium tuberculosis-infected antigen-presenting cells

Previous studies in murine models, including those using the beta2 microglobulin knockout mouse, have suggested an important role for CD8+ T cells in host defense to Mycobacterium tuberculosis (Mtb). At present, little is understood about these cells in the human immune response to tuberculosis. This report demonstrates the existence of human Mtb-reactive CD8+ T cells. These cells are present preferentially in persons infected with Mtb and produce interferon gamma in response to stimulation with Mtb-infected target cells. Recognition of Mtb-infected cells by these CD8+ T cells is restricted neither by the major histocompatibility complex (MHC) class I A, B, or C alleles nor by CD1, although it is inhibited by anti-MHC class I antibody. The Mtb-specific CD8+ T cells recognize an antigen which is generated in the proteasome, but which does not require transport through the Golgi-ER. The data suggest the possible use of nonpolymorphic MHC class Ib antigen presenting structures other than CD1.

Human purified protein derivative-specific CD4+ T cells use both CD95-dependent and CD95-independent cytolytic mechanisms

CTL, both CD4+ and CD8+, are essential in the eradication of intracellular pathogens. Data generated using murine T cells have suggested a critical role for CD95 (Fas, Apo-1) in CD4+ T cell-induced apoptosis of target cells. In contrast, CD8+ CTL predominantly use the perforin/granzyme lytic pathway. At present little is known about the mechanism of CD4+ CTL lytic function during intracellular infection in humans. We have used human CD4+ T cells specific for purified protein derivative (PPD) of Mycobacterium tuberculosis to explore whether CD95 is the dominant cytolytic mechanism. PPD-reactive CD4+ clones efficiently lysed Ag-pulsed autologous monocytes, adherent macrophages, and EBV-transformed B cells. Addition of an antagonistic CD95 Ab had a minimal effect on cytolysis, whereas addition of MgEGTA to block perforin/granzyme resulted in complete inhibition of killing. In contrast, lysis of activated peripheral blood B cells could be partially blocked with the antagonistic CD95 Ab. Supporting these observations, monocytes, macrophages, and EBV-transformed B cells were not lysed by an agonistic CD95 Ab. Activated B cells were readily lysed by the agonistic CD95 Ab. T cell clones triggered through the TCR with anti-CD3 were capable of lysing the CD95-sensitive Jurkat T cell line in a CD95-dependent manner, but were also able to release granzymes. We conclude that human CD4+ T cells are capable of lysing PPD-pulsed targets using both perforin/granzyme and CD95 pathways. The contribution of CD95 is strictly dependent on target cell susceptibility to CD95-mediated killing.

CD40 ligand inhibits Fas/CD95-mediated apoptosis of human blood-derived dendritic cells

Dendritic cells (DC) are considered to be the most potent antigen-presenting cells (APC) in the immune system. In this study, we analyzed the regulation of apoptosis of human peripheral blood-derived DC. DC were generated from adherent peripheral blood mononuclear cells that had been cultured for 7 days with granulocyte-macrophage colony-stimulating factor and interleukin-4. These cells displayed phenotypic properties of DC, including dendritic processes, expression of CD1a and lack of expression of CD14, and were very potent at presenting soluble antigens to T cells. Blood-derived DC were demonstrated to express the Fas/CD95 antigen and an agonist antibody to CD95 strongly induced apoptotic cell death in these cells. Soluble trimeric CD40 ligand potently inhibited both CD95-mediated and spontaneous apoptosis in DC. The data suggest that interactions between members of the tumor necrosis factor family of ligands expressed by T cells with their receptors on DC play an important role in the regulation of apoptosis in DC during antigen presentation and may, therefore, regulate the duration of T cell expansion and cytokine production.

Phase I study of intravenous ribavirin treatment of respiratory syncytial virus pneumonia after marrow transplantation

Respiratory syncytial virus (RSV) pneumonia in marrow transplant recipients is associated with significant mortality. Ribavirin is a nucleoside analog with activity against RSV and in its aerosolized formulation is the only drug approved for treatment of RSV pneumonia in the United States. The clinical use of aerosolized ribavirin has been limited by caregivers' concerns about drug exposure and potential teratogenic effects. Since there is lack of proven efficacy and safety of the aerosolized ribavirin in this setting, we performed a phase I study of intravenous ribavirin treatment. Between November 1993 and May 1994, 10 patients with clinically significant RSV pneumonia at the Fred Hutchinson Cancer Research Center were enrolled. Only 2 of the 10 survived (20%; 95% CI, 3-56). Two of the 10 patients developed acute hemolysis that necessitated discontinuation of the medication. In conclusion, treatment of marrow transplant recipients with RSV pneumonia with intravenous ribavirin did not improve mortality compared with historical controls treated with the aerosolized drug.

Use of polymerase chain reaction for successful identification of asymptomatic genital infection with herpes simplex virus in pregnant women at delivery

The polymerase chain reaction was adapted to the amplification of a herpes simplex virus (HSV) DNA sequence, common to HSV types 1 and 2 (HSV-1, HSV-2). The amplified product was detectable by ethidium-bromide staining or Southern hybridization of gels and by dot hybridization. The HSV polymerase chain reaction detected HSV DNA in samples obtained from eight patients with genital lesions from which HSV-2 was isolated in tissue culture and from four patients with labial lesions from which HSV-1 was isolated. The HSV polymerase chain reaction identified HSV in clinical specimens obtained from 11 women who had asymptomatic genital HSV infections at delivery. None of 11 samples obtained at delivery from women who had antibodies to HSV-2, but whose delivery cultures were negative, were positive by polymerase chain reaction and no false-positive reactions were obtained when the reaction mixture contained human cell DNA or varicella-zoster virus, cytomegalovirus, Epstein-Barr virus, or human papillomavirus DNA.

Hematopoietic progenitor cell expression of the H-CAM (CD44) homing-associated adhesion molecule

We explored the expression of a lymphocyte homing-associated cell adhesion molecule (H-CAM, CD44) on hematopoietic progenitors. We demonstrate that immature myeloid and erythroid leukemic cell lines stain intensely with monoclonal antibodies Hermes-1 and Hermes-3, which define distinct epitopes on lymphocyte surface H-CAM, a glycoprotein involved in lymphocyte interactions with endothelial cells. Using fluorescence-activated cell sorting (FACS), human marrow cells were fractionated into Hermeshi, Hermesmed, and Hermeslo populations according to the expression of both the Hermes-1 and Hermes-3 epitopes. Granulocyte-macrophage colony-forming unit and erythroid burst-forming unit precursors were found predominantly in the brightly positive fractions. Two-color FACS analysis confirmed that the My10 (CD34) positive populations of cells in bone marrow, which contain most of the progenitor cell activity, are brightly positive for Hermes-1. Finally, we demonstrate that among bone marrow cells, the highest levels of H-CAM are expressed on myeloid and erythroid progenitors as well as mature granulocytes and lymphocytes. Thus we provide evidence that molecules related or identical to the H-CAM homing receptor are expressed on marrow progenitor cells. H-CAM may contribute to progenitor cell interactions with marrow endothelial and stromal cell elements important to the maintenance and regulation of hematopoiesis.

A fluorometric approach to the quantitation of cell number with application to a cell adhesion assay

We describe a fluorometric approach to the determination of cell number. Cells are covalently labeled with fluorescein isothiocyanate (FITC) under physiologic conditions. Cells are lysed with detergent, and released fluorochrome is assessed quantitatively with a fluorescence spectrophotometer. Fluorescence varies linearly with regard to cell number over a wide range of concentrations, and allows detection of as few as 8 X 10(3) cells/ml. We describe the effect of different time and temperature incubations of FITC-labeled cells on fluorescence intensity, and we use the method to analyze the binding of peripheral blood mononuclear leukocytes to interferon-gamma-treated keratinocytes. Finally, we demonstrate that the results in an adhesion assay are comparable to those obtained with 51Cr-labeled cells. Quantitative fluorescence analysis of cell number offers a safe, inexpensive, rapid, and accurate method of determining cell number without the biological hazard and waste disposal problems associated with radioactive labeling.

Recombinant gamma interferon increases the binding of peripheral blood mononuclear leukocytes and a Leu-3+ T lymphocyte clone to cultured keratinocytes and to a malignant cutaneous squamous carcinoma cell line that is blocked by antibody against the LFA-1 molecule

Because keratinocytes (KCs) express HLA-DR in a wide variety of skin diseases in which mononuclear leukocytes are observed in close apposition to KCs (i.e., graft-versus-host disease), and since gamma interferon (IFN-gamma) induces HLA-DR expression on KCs, we asked whether IFN-gamma treatment of KCs would influence the adherence of mononuclear leukocytes. When allogeneic peripheral blood mononuclear leukocytes (PBML) and a Leu-3+ T cell clone were coincubated with IFN-gamma-treated KCs (300 U/ml, 3 days), there was a marked increase in binding compared with nontreated KCs. Similar binding results were obtained using a cutaneous squamous carcinoma cell line (SCL-1) after IFN-gamma treatment. The IFN effect was relatively specific for IFN-gamma, as neither IFN-alpha nor -beta had any effect. Tumor necrosis factor exposure (500 U/ml, 3 days) increased the binding of the Leu-3+ T cell clone to both KCs and SCL-1 cells. Neutrophils displayed a less marked (but statistically significant) increase in binding to IFN-gamma-treated KCs. Using the Leu-3+ cell clone and SCL-1 cells, detailed kinetic analysis of the effect of IFN-gamma on binding was performed. The increased adherence between the cells began to appear after only 7 hours of treatment with r-IFN-gamma (300 U/ml) and reached a plateau at 48 hours, with significantly enhanced binding continuing for at least 48 hours after removal of IFN-gamma. The mechanism of binding was explored by preincubation of the PBML/Leu-3+ T cells with anti-LFA-1 (lymphocyte function-associated antigen) antibody (0.6-6.0 micrograms/ml), which totally inhibited the binding with no effect by anti-LFA-2 or -3 or class I or II antibodies despite documented binding of these antibodies to the cells. These results suggest that, after exposure to IFN-gamma, the ability of KCs to bind mononuclear leukocytes is strongly enhanced, and this adherence may be important in leukocyte trafficking in the skin as well as contributing to altered KC-leukocyte interaction, which may be of fundamental importance in a variety of skin disease.

Enhanced binding of peripheral blood mononuclear leukocytes to gamma-interferon-treated cultured keratinocytes

Dermatopathologists observe mononuclear leukocytes in close apposition to keratinocytes (KCs) in graft versus host disease and in other lymphocyte-mediated skin diseases, such as lichen planus, erythema multiforme, and lupus erythematosus. Since the KCs are Class II histocompatibility antigen (HLA-DR) positive in these diseases (indicating local production of gamma interferon, IFN-gamma, by activated T-cells), we sought to determine whether IFN-gamma treatment of KCs would influence the ability of allogeneic peripheral blood mononuclear leukocytes (PBMLs) to adhere to cultured KCs in vitro. The adherence of PBMLs to KC monolayers was determined by the three following methods: (a) methanol fixation of the washed KCs (after PBML incubation), followed by hematoxylin-eosin staining and direct counting of adherent PBMLs; (b) fluorescein isothiocyanate (FITC) labeling of PBML, followed by measuring the amount of FITC-PBML bound to KCs after washing either by direct visualization with a fluorescence microscope; or by (c) quantitative fluorescence spectroscopy following lysis of the adherent cells. While untreated KCs bound allogeneic PBMLs minimally 15-120 min at 37 degrees C, pretreatment of the KCs with IFN-gamma (300 U/ml, 3 days) produced significantly increased binding of the PBMLs by approximately fivefold. By contrast, IFN-alpha and IFN-beta (10(3) U/ml) had no effect. Also, despite the induction of HLA-DR on cultured human fibroblasts, no increased binding of PBMLs after IFN-gamma treatment was observed. The selective ability of IFN-gamma to produce a marked increase in adherence between KCs and PBMLs suggests a new role for IFN-gamma in the immunobiology of the skin.

Leukocyte-endothelial cell recognition: evidence of a common molecular mechanism shared by neutrophils, lymphocytes, and other leukocytes

The interaction of leukocytes with endothelial cells is intrinsic to the process of leukocyte extravasation, whether during the entry of blood polymorphonuclear leukocytes and monocytes into sites of acute and chronic inflammation, or during the homing of lymphocytes to lymphoid organs. A lymphocyte surface glycoprotein, defined by monoclonal antibody MEL-14, has been described that appears to mediate lymphocyte recognition of postcapillary venules in peripheral lymph nodes, and to control the migration of lymphocytes from the blood into these lymphoid organs. We now report that the antigenic determinant recognized by MEL-14 is present at high levels on other leukocytes as well, including neutrophils, monocytes, and eosinophils; and we demonstrate involvement of the MEL-14 antigen in neutrophil-endothelial cell interactions. MEL-14 immunoprecipitates a neutrophil surface protein of Mr approximately 100,000, similar in m.w. to the 80,000 to 90,000 dalton lymphocyte surface MEL-14 antigen, and it blocks the interaction of neutrophils with endothelial cells in an in vitro model of adhesion to postcapillary venules in lymph node frozen sections. Neutrophil binding to lymph node venules is also inhibited by PPME, a mannose-6-phosphate-rich yeast polysaccharide that is thought to mimic the endothelial cell ligand for the MEL-14-defined lymphocyte receptor. Interestingly, neither MEL-14 nor PPME exhibit a major effect on neutrophil binding to postcapillary venules in Peyer's patches, suggesting that as for lymphocytes, the neutrophil MEL-14 antigen is involved in recognition of tissue-specific endothelial determinants. Finally, we show that MEL-14 inhibits the capacity of neutrophils to migrate from the blood into sites of acute inflammation in the skin. These observations lead us to propose that receptors for tissue-specific endothelial determinants are utilized by neutrophils and lymphocytes and probably other leukocytes during the physiologic process of leukocyte extravasation in vivo.

Leukocyte-endothelial cell recognition: evidence of a common molecular mechanism shared by neutrophils, lymphocytes, and other leukocytes

The interaction of leukocytes with endothelial cells is intrinsic to the process of leukocyte extravasation, whether during the entry of blood polymorphonuclear leukocytes and monocytes into sites of acute and chronic inflammation, or during the homing of lymphocytes to lymphoid organs. A lymphocyte surface glycoprotein, defined by monoclonal antibody MEL-14, has been described that appears to mediate lymphocyte recognition of postcapillary venules in peripheral lymph nodes, and to control the migration of lymphocytes from the blood into these lymphoid organs. We now report that the antigenic determinant recognized by MEL-14 is present at high levels on other leukocytes as well, including neutrophils, monocytes, and eosinophils; and we demonstrate involvement of the MEL-14 antigen in neutrophil-endothelial cell interactions. MEL-14 immunoprecipitates a neutrophil surface protein of Mr approximately 100,000, similar in m.w. to the 80,000 to 90,000 dalton lymphocyte surface MEL-14 antigen, and it blocks the interaction of neutrophils with endothelial cells in an in vitro model of adhesion to postcapillary venules in lymph node frozen sections. Neutrophil binding to lymph node venules is also inhibited by PPME, a mannose-6-phosphate-rich yeast polysaccharide that is thought to mimic the endothelial cell ligand for the MEL-14-defined lymphocyte receptor. Interestingly, neither MEL-14 nor PPME exhibit a major effect on neutrophil binding to postcapillary venules in Peyer's patches, suggesting that as for lymphocytes, the neutrophil MEL-14 antigen is involved in recognition of tissue-specific endothelial determinants. Finally, we show that MEL-14 inhibits the capacity of neutrophils to migrate from the blood into sites of acute inflammation in the skin. These observations lead us to propose that receptors for tissue-specific endothelial determinants are utilized by neutrophils and lymphocytes and probably other leukocytes during the physiologic process of leukocyte extravasation in vivo.