In vitro positive selection and anergy induction of class II-restricted TCR transgenic thymocytes by a cortical thymic epithelial cell line

Thymic epithelial cell lines isolated from hyperplastic thymi of transgenic mice over-expressing human papilloma viral oncogenes E6 and E7 constitutively displayed a phenotype consistent with a cortical origin. Exposure to IFN-gamma induced class II MHC and ICAM-1 expression, and up-regulated expression of VCAM-1 and class I MHC molecules. CD40 expression was maximally induced by a combination of IFN-gamma and IL-1, with lower levels of induction observed with a mixture of IFN-gamma and tumor necrosis factor (TNF)-alpha or TNF-alpha alone. B7-1 or B7-2 was not expressed constitutively or in response to cytokines. These stromal cells supported the development of CD4 single-positive (SP) cells in reaggregate co-cultures with CD4+ CD8+ thymocytes from TCR transgenic mice, but did not stimulate class II MHC-restricted, moth cytochrome c (MCC)-reactive T cells in vitro. The behavior of the culture system was consistent with positive selection, i.e. increased numbers of CD4 SP cells, gain of antigen responsiveness, and requirement for epithelial class II MHC products. Some variants of these stromal cell lines required exogenous MCC peptide in the reaggregation cultures (RC) for positive selection to occur. While a low concentration of MCC peptide (0.01-0.1 microM) significantly enhanced the accumulation of CD4 SP cells, higher concentrations of peptide (1-10 microM) resulted in recovery of predominantly CD4- CD8- and CD4(low) CD8- cells. Thymocytes recovered from RC containing low, but not high concentrations of peptide responded to MCC peptide in secondary cultures with splenic antigen-presenting cells.     

Impaired categorical perception of synthetic speech sounds in schizophrenia

BACKGROUND: The rationale for the study was based on the hypothesis that decreased or absent expression on tumor cells of adhesion molecules, the class I or class II major histocompatibility complex (MHC) molecules, or costimulatory molecules might be responsible, in part, for the poor ability of squamous cell carcinoma of the head and neck (SCCHN) to induce generation of antitumor effector cells in vitro and in vivo. OBJECTIVE: To investigate expression of intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function associated antigen-3 (LFA-3) and distribution of the costimulatory molecules, B7.1, B7.2, and CD40, and of class I and class II MHC molecules on SCCHN cells in situ and on SCCHN cell lines. SETTING: University medical centers. DESIGN: Expression of ICAM-1, LFA-3, MHC molecules, B7.1, B7.2, and CD40 was evaluated in human SCCHN biopsy specimens by immunohistochemistry and on SCCHN cell lines by flow cytometry. To confirm our hypothesis that impaired T-cell activation observed in patients with SCCHN is caused by the absence of costimulatory B7 molecules, a B7-negative SCCHN cell line was transduced with the B7.1 gene, using a retroviral vector, and tested in mixed lymphocyte tumor cocultures. RESULTS: In contrast to abundant expression of ICAM-1, LFA-3, class I MHC molecules, and CD40, the absence of B7.1, B7.2, and class II MHC molecules on tumor cells was observed in situ and in vitro. Lymphocytes and antigen-presenting cells in inflammatory infiltrates surrounding tumor cell clusters expressed both costimulatory and adhesion molecules. The SCCHN lines negative for B7.1 and class II MHC antigens failed to induce proliferation of T cells in mixed lymphocyte tumor cocultures. However, when these cell lines were transduced with the B7.1 gene, their ability to induce T-cell proliferation in mixed lymphocyte tumor cocultures was restored. CONCLUSIONS: The absence of B7 protein or class II MHC antigen expression on human SCCHN cells is responsible for the failure of these tumors to induce proliferation of T cells in vitro. Transduction of the B7.1 gene into SCCHN restores the ability of the tumor to induce T-cell proliferation in vitro.     

A comparison of the antigen-presenting capabilities of class II MHC-expressing human lung epithelial and endothelial cells

Human lung alveolar epithelial cells constitutively express class II major histocompatibility complex (MHC). Human lung microvascular endothelial and small airway epithelial cells can be induced to express class II MHC by stimulation with the pro-inflammatory cytokine interferon-gamma. The levels of class II MHC on lung epithelial and endothelial cells were comparable to those seen on an Epstein-Barr virus (EBV)-transformed B-cell line. However, the costimulatory molecules B7-1 and B7-2 were not expressed. The ability of the class II MHC expressing human lung parenchymal cells to present alloantigen to CD4+ T lymphocytes was investigated. Freshly isolated human alveolar epithelial cells (type II pneumocytes) and monolayers of interferon-gamma-stimulated small airway epithelial and lung microvascular endothelial cells were co-cultured with allogeneic CD4+ T lymphocytes and proliferation determined by [3H]thymidine incorporation. A clear difference was observed between effects of the epithelial and endothelial cells on CD4+ T-lymphocyte activation. Alveolar and small airway epithelial cells failed to stimulate the proliferation of allogeneic CD4+ T lymphocytes whereas lung microvascular endothelial cells did stimulate proliferation. This difference could not be explained by the levels of class II MHC or the lack of B7-1 and B7-2 solely. Microvascular endothelial cells, and not alveolar or small airway epithelial cells, possess B7-independent costimulatory pathways.     

Effects of dietary supplementation with alpha-linolenic acid on the phospholipid fatty acid composition and quality of spermatozoa in cockerel from 24 to 72 weeks of age

The physiopathology of experimental cerebral malaria (CM), an acute neurological complication of Plasmodium berghei ANKA (PbA) infection, involves interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha), two cytokines that are known to modulate major histocompatibility complex (MHC) molecule expression. The aim of this study was to evaluate whether the genetic susceptibility to CM is related to the constitutive or IFN-gamma-induced expression of MHC molecules on brain microvessels. To this end, brain microvascular endothelial cells (B-MVEC) were isolated from CM-susceptible (CM-S, CBA/J) and resistant (CM-R, BALB/c) mice. By flow cytometry, we found that less than 5% of CM-S B-MVEC constitutively expressed MHC class I molecules, in contrast to up to 90% of CM-R B-MVEC. Upon stimulation with IFN-gamma, the percentage of positive cells for MHC class I molecules in CM-S B-MVEC became comparable to CM-R B-MVEC, but a higher fluorescence intensity existed on CM-S B-MVEC compared with CM-R B-MVEC. MHC class II molecules were not constitutively expressed on B-MVEC from either strain. IFN-gamma-induced expression of MHC class II (I-A, I-E) molecules was significantly higher in CM-S than CM-R B-MVEC both in percentage of positive cells and fluorescence intensity. These data demonstrate that absent or low MHC class I and higher inducibility of MHC class II expression on B-MVEC are associated with the genetic susceptibility to CM.     

Anticryptococcal activity by alveolar macrophages from rats treated with cortisone acetate during different periods of time

Recently mouse models have shown that expression of costimulatory molecules such as B7-1 on tumor cells can induce tumor-specific immunity, suggesting that tumor cells modified to express costimulatory molecules can be a potential tumor vaccine. To investigate the importance of B7-1 co-stimulation in induction of autologous tumor immunity in humans, we established a renal carcinoma cell line, RCC-1, from a tumor resection and studied the patient's antitumor immune responses in vitro. The RCC-1 cell line constitutively expressed major histocompatibility complex (MHC) class I, intercellular adhesion molecule (ICAM)-1, and leukocyte function-associated antigen (LFA)-3 molecules, and MHC class II molecules were induced by interferon-gamma (IFN-gamma) treatment in vitro. However, neither RCC-1- nor IFN-gamma-treated RCC-1 cells expressed B7-1, and both failed to induce T-cell proliferative responses in mixed lymphocyte and tumor cell reaction (MLTR) assays, suggesting that the costimulatory signals provided by cell adhesion molecules such as ICAM-1 and LFA-3 were not sufficient to elicit an antitumor immune response. However, on transfection of the human B7-1 into RCC-1, these cells were able to induce a significant T-cell proliferation in MLTR assays. This T-cell response could be blocked by anti-B7 mAb treatment of the tumor cells. RCC-1B7 cells also induced the generation of tumor-specific cytolytic T lymphocytes to the parent RCC-1 cells in vitro, with little nonspecific cytolysis of an unrelated RCC line, A498, or autologous phytohemagglutinin (PHA) blasts. This specific cytotoxicity could be abrogated by anti-CD8 mAb and complement treatment. In summary, our study indicates that B7-1-CD28 interaction plays a critical role in induction of autologous tumor-specific cytotoxic T lymphocytes (CTLs) in humans, suggesting that the costimulatory molecule transfected tumor cells could be useful in expanding tumor-specific autologous CTL in vitro for adoptive tumor immunotherapy.     

Renal allograft rejection: protection of renal epithelium from natural killer cells by cytokine-induced up-regulation of class I major histocompatibility antigens

The potential of natural killer (NK) cells to contribute to renal allograft rejection was modelled by mixing NK cells with cultured renal epithelial cells. It was found that the renal cells were readily lysed by cytokine-activated NK cells. Renal cells which were previously stimulated by culture with either interferon-gamma (IFN-gamma) or supernatant from mixed leucocyte cultures (MLC) were relatively resistant to such lysis; stimulation with tumour necrosis factor-alpha (TNF-alpha) had no effect. None of these cytokine preparations had any effect on the lysis of renal cells by either specific cytotoxic T lymphocytes or the antibody-dependent cell-mediated cytotoxic mechanism. The expression of class I major histocompatibility complex (MHC) antigens was up-regulated by stimulation of renal cells with either IFN-gamma or MLC supernatant; treatment with TNF-alpha had no effect on the expression of these antigens. Protection from NK cell-mediated lysis appeared to correlate with the expression of class I MHC antigens by the renal cells. Artificial removal of these MHC antigens by treatment with citric acid significantly increased the susceptibility of cytokine-stimulated renal cells to lysis by activated NK cells. This increase was not caused by enhanced binding of NK cells to acid-treated renal cell targets. These results suggest that high levels of class I MHC antigen expression block NK cell triggering after engagement with renal epithelial cells. It is concluded that cytokines present within the renal microenvironment during rejection protect graft cells from lysis by NK cells by causing local upregulation of the expression of class I MHC molecules.     

Resistance of Indonesian thin tail sheep against Fasciola gigantica and F. hepatica

Astrocytes express variable levels of MHC class II antigens depending on their activation status or exposure to certain cytokines, notably IFN-gamma. When they are induced to express higher surface densities of MHC class II molecules, astrocytes are capable of stimulating syngeneic myelin basic protein (MBP)-reactive T cells to proliferate at a modest rate and to secrete proinflammatory cytokines, such as TNF-alpha, in response to antigen. In the present investigation evidence is presented that uninduced astrocytes, whether fresh or established as clones, on which surface MHC class II molecules are expressed at a very low density, promote an antigen-dependent reduction of TCR on the surface of syngeneic T cells. Accompanying this effect on the TCR is an induction of T cell hyporeactivity and little or no production of proinflammatory cytokines. These observations suggest that the ability of the astrocyte, through varying their surface MHC class II molecules, can control the effect of antigen-induced T cell responses. In their normal state of low MHC II expression astrocytes are expected to induce no or partial, rather than full, activation of autoreactive T cells that enter the CNS, resulting in T cell hyporeactivity. Since astrocytes usually diminish the production of proinflammatory cytokines by T cells that enter the CNS, the status and control of MHC class II expression on astrocytes should be important determinants of the suppression or enhancement of in situ immune responses in the CNS.     

1,25-dihydroxycholecalciferol enhances the expression of MHC class II antigens and intercellular adhesion molecule-1 by human renal tubular epithelial cells

PURPOSE: Beside its role in calcium and phosphorus metabolism, 1,25-dihydroxycholecalciferol (1,25-D3) exerts multiple effects on cytokine and major histocompatibility complex (MHC) class II expression in monocytes and lymphocytes. In different renal diseases tubular epithelial cells express MHC class II molecules and cell adhesion molecules,, such as intracellular adhesion molecule-1 (ICAM-1). Therefore, modulation of MHC class II and ICAM-1 expression in renal tubular epithelial cells by 1,25-D3 may be relevant to lymphocyte adhesion to tubular epithelial cells and immune mediated renal injury. However, the expression of MHC class II antigens and cellular adhesion molecules by renal tubular epithelial cells in response to 1,25-D3 has not been investigated. MATERIALS AND METHODS: We generated human renal tubular epithelial cells and SV40 transfected tubular epithelial cells to investigate immune modulation of 1,25 on renal epithelial cells. Major histocompatibility complex class II molecules and ICAM-1 were detected by a specific enzyme linked immunoassay. RESULTS: We found a dose-dependent increase of both constitutive and induced MHC class II and ICAM-1 expression in tubular epithelial cells stimulated with 1,25-D3. Dose-dependent stimulation of MHC class II and ICAM-1 expression was not restricted to primary human renal tubular epithelial cells but was also detected in SV40 transfected cells. CONCLUSIONS: Expression of MHC class II and ICAM-1 is crucial for antigen presentation by and lymphocyte adhesion to renal tubular epithelial cells. Modulatory effects of 1,25-D3 on immune accessory function of renal tubular epithelial cells may be of clinical significance in renal diseases.     

Characterization of and functional antigen presentation by central nervous system mononuclear cells from mice infected with Theiler's murine encephalomyelitis virus

We examined the phenotype and function of cells infiltrating the central nervous system (CNS) of mice persistently infected with Theiler's murine encephalomyelitis virus (TMEV) for evidence that viral antigens are presented to T cells within the CNS. Expression of major histocompatibility complex (MHC) class II in the spinal cords of mice infected with TMEV was found predominantly on macrophages in demyelinating lesions. The distribution of I-As staining overlapped that of the macrophage marker sialoadhesin in frozen sections and coincided with that of another macrophage/microglial cell marker, F4/80, by flow cytometry. In contrast, astrocytes, identified by staining with glial fibrillary acidic protein, rarely expressed detectable MHC class II, although fibrillary gliosis associated with the CNS damage was clearly seen. The costimulatory molecules B7-1 and B7-2 were expressed on the surface of most MHC class II-positive cells in the CNS, at levels exceeding those found in the spleens of the infected mice. Immunohistochemistry revealed that B7-1 and B7-2 colocalized on large F4/80(+) macrophages/microglia in the spinal cord lesions. In contrast, CD4(+) T cells in the lesions expressed mainly B7-2, which was found primarily on blastoid CD4(+) T cells located toward the periphery of the lesions. Most interestingly, plastic-adherent cells freshly isolated from the spinal cords of TMEV-infected mice were able to process and present TMEV and horse myoglobin to antigen-specific T-cell lines. Furthermore, these cells were able to activate a TMEV epitope-specific T-cell line in the absence of added antigen, providing conclusive evidence for the endogenous processing and presentation of virus epitopes within the CNS of persistently infected SJL/J mice.     

Human parainfluenza virus type 3 up-regulates major histocompatibility complex class I and II expression on respiratory epithelial cells: involvement of a STAT1- and CIITA-independent pathway

Human parainfluenza virus type 3 (HPIV3) infection causes severe damage to the lung epithelium, leading to bronchiolitis, pneumonia, and croup in newborns and infants. Cellular immunity that plays a vital role in normal antiviral action appears to be involved, possibly because of inappropriate activation, in the infection-related damage to the lung epithelium. In this study, we investigated the expression of major histocompatibility complex (MHC) class I and II molecules on human lung epithelial (A549) and epithelium-like (HT1080) cells following HPIV3 infection. MHC class I was induced by HPIV3 in these cells at levels similar to those observed with natural inducers such as beta and gamma interferon (IFN-beta and -gamma). MHC class II was also efficiently induced by HPIV3 in these cells. UV-irradiated culture supernatants from infected cells were able to induce MHC class I but not MHC class II, suggesting involvement of released factors for the induction of MHC class I. Quantitation of IFN types I and II in the culture supernatant showed the presence of IFN-beta as the major cytokine, while IFN-gamma was undetectable. Anti-IFN-beta, however, blocked the HPIV3-mediated induction of MHC class I only partially, indicating that viral antigens, besides IFN-beta, are directly involved in the induction process. The induction of MHC class I and class II directed by the viral antigens was confirmed by using cells lacking STAT1, an essential intermediate of the IFN signaling pathways. HPIV3 induced both MHC class I and class II molecules in STAT1-null cells. Furthermore, MHC class II was also induced by HPIV3 in cells defective in class II transactivator, an important intermediate of the IFN-gamma-mediated MHC class II induction pathway. Together, these data indicate that the HPIV3 gene product(s) is directly involved in the induction of MHC class I and II molecules. The induction of MHC class I and II expression by HPIV3 suggests that it plays a role in the infection-related immunity and pathogenesis.     

Microglia are more efficient than astrocytes in antigen processing and in Th1 but not Th2 cell activation

Microglia and astrocytes, two glial cell populations of the central nervous system, present Ag and stimulate T cell proliferation, but it is unclear whether they preferentially activate Th1 or Th2 responses. We have investigated the efficiency of microglia and astrocytes in the presentation of OVA peptide 323-339 or native OVA to Th1 and Th2 cell lines from DO11.10 TCR transgenic mice. Upon stimulation with IFN-gamma, microglia express MHC class II molecules, CD40, and ICAM-1 and efficiently present OVA 323-339, leading to T cell proliferation and production of IL-2 and IFN-gamma by Th1 and of IL-4 by Th2 cells. IFN-gamma-treated astrocytes, which express MHC class II and ICAM-1, present OVA 323-339 less efficiently to Th1 cells but are as efficient as microglia in inducing IL-4 secretion by Th2 cells. However, astrocytes are much less potent than microglia in presenting naturally processed OVA peptide to either T cell subset, indicating inefficient Ag processing. The capacity of astrocytes and microglia to stimulate Th1 and Th2 cells depends on their MHC class II expression and does not involve ICAM-1, B7-1, or B7-2 molecules. However, CD40-CD40L interactions contribute to Th1 activation by microglia. These data suggest that microglia may play a role in the activation of Th1 and Th2 cells, whereas astrocytes would restimulate mainly Th2 responses in the presence of appropriate peptides. This differential capacity of brain APC to restimulate Th1 and Th2 responses may contribute to the reactivation and regulation of local inflammatory processes during infectious and autoimmune diseases.     

Sleep-disordered breathing in children

It is demonstrated that methotrexate/cisplatin-sensitive L1210 cells express low levels of major histocompatibility complex (MHC) class II relative to the high levels expressed on methotrexate (MTX)/cisplatin-resistant L1210/DDP cells. L1210 cells express cell-surface Fas, while the L1210/DDP cells express no cell-surface Fas. Expression of costimulatory molecules B7-1/B7-2 and Fas is increased on L1210 cells, but not L1210/DDP, in the presence of methotrexate or trimetrexate (TMTX). Therefore, a component of the mechanism of action of some anti-cancer agents may be to facilitate immune recognition and T cell-directed, Fas-induced cell death. Loss of cell-surface Fas expression and failure of Fas (CD95)-dependent apoptotic death has been observed when cells develop drug resistance. The defect in apoptosis can be overcome by anti-cancer agents or experimental manipulation that induce Fas expression on the drug-resistant cells.     

Compensation for decreased expression of B7 molecules on Leishmania infantum-infected canine macrophages results in restoration of parasite-specific T-cell proliferation and gamma interferon production

Infection of humans and dogs by Leishmania infantum may result in visceral leishmaniasis, which is characterized by impaired T-cell-mediated immune responses to parasite antigens. Dogs are natural hosts of Leishmania parasites and play an important role in the transmission of the parasites to humans. In an effort to characterize the immune response in dogs infected with this intracellular pathogen, we examined how infection with L. infantum affects canine macrophages and the consequences for T-cell activation in vitro. We showed that the proliferation of T-cell lines to cognate antigen decreases to background levels when infected autologous monocyte-derived macrophages are used as antigen-presenting cells (APC). The observed reduction of antigen-specific T-cell proliferation was shown to be dependent on the parasite load and to require cell-to-cell interaction of T cells with the infected APC. In addition, we observed a decreased expression of costimulatory B7 molecules on infected monocyte-derived macrophages. The expression of other surface molecules involved in T-cell activation, such as major histocompatibility complex class I and class II, on these cells did not change upon infection, whereas the expression of intracellular adhesion molecule 1 was marginally increased. Compensation for the decreased expression of B7 molecules by the addition of B7-transfected cells resulted in the restoration of cell proliferation and gamma interferon (IFN-gamma) production by a Leishmania-specific T-cell line. These results showed that for the activation of parasite-specific canine T cells producing IFN-gamma, which are most likely involved in protective immunity, sufficient expression of B7 molecules on infected macrophages is required. Provision of costimulatory molecules may be an approach for immunotherapy of leishmaniaisis as well as for vaccine development.     

Protective effects of interferon-gamma in intraocular herpes simplex type 1 infection do not depend on major histocompatibility complex class I or class II expression

Intraocular infection with herpes simplex virus type I strain F (HSV-1) induces bilateral retinitis, the expression of both MHC class I and II molecules and activation of CD4 and CD8 cells. To investigate the role of MHC upregulation in IFN-gamma mediated antiviral effects in intraocular infection with HSV-1, we infected MHC deficient mice and mice with an additional ectopic site of IFN-gamma production in their retina (rho gamma) intravitreally with HSV-1 into one eye. Protective effects of IFN-gamma in intraocular HSV-1 infection were notable as sparing of the contralateral non-inoculated eye from retinitis, and were not dependent on MHC class I and class II expression, thus limiting the importance of MHC expression for the outcome of viral infection in vivo.     

Wound and skin care for the PICU

The consequence of recognition of antigen on antigen-presenting cells that are induced to express major histocompatibility complex (MHC) class II molecules following an inflammatory process is still not clear. In this study, we have investigated the outcome of antigen presentation by epithelial cells and we have used as a model thyroid follicular cells (TFC) that are known to express MHC class II molecules in autoimmune thyroid diseases and acquire the capacity to present autoantigens to T cells infiltrating the thyroid gland. The result show that MHC class II-expressing TFC were unable to stimulate a primary T cell alloresponse, using CD4+ T cells from three HLA-mismatched responders. Phenotypic analysis showed that TFC, after incubation with interferon-gamma, do not express the costimulatory molecules B7-1 (CD80) and -2 (CD86). Addition of murine DAP.3 cells expressing human B7-1 (DAP.3-B7) to cultures containing peripheral blood CD4+ T cells and DR1-expressing TFC led to a proliferative response, suggesting that the failure of TFC to stimulate a primary alloresponse was due to a lack of co-stimulation. Similarly, HLA-DR-restricted, influenza-specific T cell clones dependent on B7 for co-stimulation did not respond to peptide presented by TFC; again the lack of response could be overcome by co-culture of TFC with DAP.3-B7. Furthermore, recognition of antigen on TFC inhibited interleukin-2 (IL-2) production in the B7-dependent T cells. In contrast, in T helper type 0 (Th0) T cells, IL-4 release was not affected by TFC presentation. In addition, antigen presentation by TFC favored IL-4 production relative to IL-2 production by B7-independent Th0 clones. These results suggest that antigen presentation by MHC class II+ TFC may induce tolerance in autoreactive Th1 cells but may simultaneously favors a Th2 response in uncommitted T cells, and thereby support autoantibody production.     

Disturbed MHC regulation in the IFN-gamma knockout mouse. Evidence for three states of MHC expression with distinct roles for IFN-gamma

We compared the expression of MHC class I and II products in tissues of IFN-gamma knockout (GKO) vs normal (wild-type) BALB/c mice. We studied expression in the basal state, after local tissue injury, after stimuli that induce systemic MHC expression (allogeneic cells, oxazolone skin painting, or LPS), and after rIFN-gamma. Basal class II expression in interstitial cells was not reduced in GKO mice. However, GKO mice had less basal class I expression in kidney, liver, heart, and arterial endothelium than wild-type mice. Local renal ischemic injury increased class I and II expression in kidney tubules of both GKO and wild-type mice, but induction in GKO was less than in wild-type. Potent inflammatory stimuli increased systemic MHC class I and II markedly in kidney, liver, and heart of wild-type mice, but induced no increase in GKO mice. rIFN-gamma induced class I and II equally in GKO and wild-type mice. Thus, three states of MHC expression can be defined that differ in their dependencies on IFN-gamma: basal, locally induced, and systemically induced. Basal class II expression in interstitial cells is IFN-gamma independent, but basal class I expression, particularly in arterial endothelium, is partially dependent on IFN-gamma. The local increase in MHC class I and II in parenchymal cells in response to injury reflects both IFN-gamma and a non-IFN-gamma factor. Systemic MHC class I and II induction is almost exclusively due to IFN-gamma.     

Specific stabilization of the 4F7 molecule on dendritic cells by contact allergens

Our laboratory has recently developed the monoclonal antibody 4F7 which recognizes a molecule on dendritic cells in the dermis of mice that is upregulated after application of contact allergens in vivo. Furthermore, this antibody detects an antigen on dendritic cells in spleen, lymph nodes and colon. In order to study the influence of contact allergens on the surface expression of the 4F7 molecules on dendritic cells, FACScan analysis of splenic dendritic cells was carried out after in vitro application of contact allergens. Freshly isolated splenic dendritic cells were found to be positive for 4F7, 33D1, N418 (CD11c) and MHC class II. After overnight culture the expression of the dendritic cell-specific molecules 4F7 and 33D1 was decreased. This downregulation was not inhibited by the addition of the cytokines TNF-alpha or GM-CSF during in vitro culture. However, in vitro treatment of freshly isolated dendritic cells with the contact allergen 2,4-dinitrofluorobenzene prevented this downregulation of the 4F7 surface molecules. The same effect was observed after treatment with other contact allergens (1-chloro-2,4-dinitrobenzene or potassium dichromate). Treatment with the irritant substance sodium dodecyl sulphate, the lectins concanavalin and lipopolysaccharide or the phorbol ester PMA did not prevent the downregulation of 4F7 and 33D1. Moreover, the influence of contact allergens on the expression of the molecules 4F7 and 33D1 was not inhibited by the protein synthesis inhibitor cycloheximide. No effects of contact sensitizers were detectable on the expression of MHC class II molecules or the costimulatory molecules B7 and heat-stable antigen. Our results show a specific stabilizing effect of contact allergens on the dendritic cell-specific molecules 4F7 and 33D1 independent of de novo protein synthesis.