The functional CD40 antigen of fibroblasts may contribute to the proliferation of rheumatoid synovium

This paper demonstrates that CD40 is expressed on rheumatoid synovial pannus and primary fibroblast cell lines established from rheumatoid and osteoarthritic synovium as well as normal skin. Among various tested cytokines, interferon-gamma (IFN-γ) and to a lower extent, tumour necrosis factor-alpha (TNF-α) were found to upregulate CD40 expression on fibroblasts. Synovial and skin fibroblasts cultured over CD40 Ligand transfected L cells (L-CD40 L) demonstrate a CD40 specific increase of DNA synthesis as measured by tritiated thymidine incorporation. Cell-cycle analysis and enumeration of viable cells further show that CD40 induced fibroblast proliferation. Costimulation with L-CD40 L and IFN-γ resulted in maximal proliferation. Engagement of fibroblasts CD40 increased the IL-1-induced production of granulocyte macrophage-colony stimulating factor and macrophage inflammatory protein-1α MIP-1α. CD40 L activated fibroblasts showed decreased levels of CD40, but only marginal alterations of other cell-surface antigens. Taken together, the present results indicate that fibroblasts express functional CD40 and suggest a possible role of CD40 L expressing cells, such as activated T cells and mast cells, in the development of synovium hyperplasia.     

Cell-cell contacts with epithelial cells modulate the phenotype of human macrophages

Interactions of macrophages with epithelium represent one of the pathways involved in regulating local immune mechanisms. We studied the effect of cell–cell contact with an epithelial monolayer on the phenotype of macrophages. Human monocytes and THP-1 macrophages were co-cultured with monolayers of human bronchial epithelial cells (HBECs), the alveolar type II-like cell line A549, renal adenocarcinoma epithelial cells (RA), and the lung fibroblast strain HFL-1. The expression of CD11b, CD14, CD54, and HLA-DR was measured by immunocytochemistry and flow cytometry and showed epithelial cell induction of CD54 and HLA-DR in monocytes and of all antigens in THP-1 cells. Co-culture with fibroblasts did not change the phenotype of macrophages. Separation by a filter insert inhibited most of the effects. Culture supernatants did not induce prominent phenotypic changes. Cell–cell contacts with epithelium appear to be of importance in regulating the phenotype of macrophages.     

Adhesion molecule-mediated signals regulate major histocompatibility complex-unrestricted and CD3/T cell receptor-triggered cytotoxicity.

Appropriate experimental conditions were devised to demonstrate that CD58 (LFA-3), CD54 (ICAM-1) and CD11a/CD18 (LFA-1) adhesion molecules are the source of signals that regulate nonspecific major histocompatibility complex-unrestricted and CD3/T cell receptor (TcR)-triggered cytotoxicity. Using anti-LFA-3 monoclonal antibody (mAb)-treated, interleukin-2 (IL-2)-cultured peripheral blood lymphocytes (PBL) or cloned CD3+/CD8+ cells as lymphocyte-activated killer (LAK) effectors, and ligand (CD2)-negative tumor cell lines as targets, a down-regulation of CD3- and CD3+ cell-mediated LAK activity was consistently observed. Anti-LFA-3 mAb also down-regulated tumor cell lysis when T cell clones were triggered to kill P815 cells through stimulation of the CD3/TcR complex by an anti-CD3 mAb. The inhibitory effect of anti-LFA-3 mAb was not prevented by stimulatory anti-CD2 mAb. Anti-ICAM-1 mAb treatment of IL-2-cultured PBL consistently up-regulated LAK cytotoxicity against tumor target cells. However, this effect was only exerted on CD3- LAK effectors. Anti-LFA-1 mAb blocked conjugate formation between effector cells and tumor target cells, thus rendering this model unsuitable to evaluate the regulatory role of LFA-1. Therefore, a cytotoxicity model system was applied in which a hybrid anti-CD3/anti-human red blood cell (HuRBC) mAb triggers cytolytic T cells to lyse HuRBC. In these experiments, anti-LFA-1 mAb markedly up-regulated the lytic ability of IL-2-cultured PBL. We conclude that mAb against LFA-3, ICAM-1 and LFA-1 molecules deliver regulatory signals for LAK cells and cytotoxic T lymphocytes. As these stimuli may be delivered by ligands expressed on tumor targets as well as on other immune competent and inflammatory cells, the present observations are relevant in the context of both the host's immune response against tumors and the general functioning of the immune system.     

Cytolysis of human dendritic cells by autologous lymphokine-activated killer cells: participation of both T cells and NK cells in the killing.

Dendritic cells (DC) play a key role in the initiation of immune response by stimulating the naive T cells. The fate of DC after the initiation of immune response is not clearly understood. Although there are few reports implicating natural killer (NK) cells in the elimination of DC, killing of DC by LAK cells, and specifically by T cells, has not been studied. In this study, we observed that DC, generated from monocytes, in vitro in the presence of granulocyte-macrophage colony-stimulating factor, interleukin-4 (IL-4), and tumor necrosis factor alpha were susceptible to cytolysis by lymphokine-activated killer (LAK) cells induced in the presence of IL-2 and IL-15 but not IL-12 alone. However, LAK cells induced by a combination of IL-12 and suboptimal dose of IL-2 were cytotoxic to DC. When purified lymphocytes were activated with IL-2, the CD8+/CD57- fraction (T-LAK), but not the CD8-/CD57+ fraction (NK-LAK) was cytotoxic to autologous DC. However, when unseparated peripheral blood mononuclear cells were used to generate LAK cells, both T-LAK and NK-LAK fractions showed equal cytotoxicity against autologous DC. Monoclonal antibodies against CD54, CD11a, and CD18 significantly inhibited the cytolysis, indicating that the killing involves the engagement of CD54 with its ligands.     

Effects of mizolastine in vitro on human immunocompetent and airway cells: evidence for safety and additional property

BACKGROUND: Mizolastine is a potent, peripherally acting, selective H1-receptor antagonist with potential anti-inflammatory properties. The aim of the study was to evaluate the in vitro effects of mizolastine on the expression of adhesion molecules by primary human airway epithelial and stromal cultures; moreover, the activity of mizolastine on parameters which reflect the immune response efficacy was investigated. METHODS: Airway epithelial and stromal cells were collected from hypereosinophilic subjects by enzymatic digestion of polyps or turbinates. Cells were stimulated with interferon (IFN)-gamma (500 IU/ml) in the presence of various mizolastine concentrations (6 x 10(-8)-6 x 10(-6) M) for 24 h and the expression of CD106, CD54, CD58 and HLA class I was evaluated. Peripheral blood mononuclear cells from healthy volunteers were incubated with 1% phytohemagglutinin or anti-CD3 monoclonal antibody (20 ng/ml) in the presence of mizolastine, then T lymphocyte proliferation, HLA-DR expression and T cell subpopulations were evaluated. RESULTS: Both in epithelial and stromal cultures, IFN-gamma significantly upregulated all of the tested surface molecules (p<0.05). The highest dose of mizolastine (6 x 10(-6) M), corresponding to 10-fold the peak plasma level after a single oral administration of 10 mg, was able to act on fibroblasts, significantly downregulating the expression of CD54 (p<0.05). Regarding T lymphocyte proliferation, the addition of mizolastine did not induce any significant change; furthermore, mizolastine was ineffective at all of the tested concentrations on both HLA-DR expression and CD4+/CD8+ ratio. CONCLUSIONS: This study demonstrated that mizolastine is able to selectively downregulate CD54 expression on stimulated stromal but not epithelial cells without impairing the immune system effectors. The possible clinical significance of these results are an antiallergic property and CD54 modulation on fibroblasts with a good safety profile as far as the lymphocyte response is concerned.     

CD54和HLA-ABC在肝癌、肝硬化组织中的表达

目的：研究ＣＤ５４ 及ＨＬＡＡＢＣ 在肝细胞肝癌（ ＨＣＣ） 及肝硬化（ＬＣ） 组织中的表达、定位及其意义。方法：以免疫组化ＡＰＡ 法,检测ＣＤ５４ 和ＨＬＡＡＢＣ 在ＨＣＣ 及ＬＣ 组织中的表达和定位。结果：ＣＤ５４ 在ＨＣＣ 组织中的阳性率为７７ ．１ ％ （３７／ ４８） , 且以膜表达为主, 呈蜂窝样排列; 在ＬＣ 组织中的阳性率为４０ ．０ ％ （１２／ ３０） , 以核表达为主。ＨＬＡＡＢＣ 在ＨＣＣ 组织中的阳性率为３０ ．０ ％ （１２／４０） ,在ＬＣ 组织中的阳性率为６３ ．３ ％ （１９／３０） 。ｘ２ 检验,ＨＣＣ 组织中ＣＤ５４ 的表达高于ＬＣ,两者相差显著（ Ｐ＜ ０ ．０５） ,Ｐｏ ｗｅｒ ＝ ０ ．９２ 。ＨＣＣ 组织中ＨＬＡＡＢＣ 的表达低于ＬＣ,两者相差显著（ Ｐ ＜ ０ ．０５） ,Ｐｏｗｅｒ ＝ ０ ．８０ 。结论：ＣＤ５４ 在ＨＣＣ 组织中的高度表达并不能引起有效抗肿瘤免疫应答,原因之一可能是ＨＬＡＡＢＣ 在ＨＣＣ 组织中的表达率降低所致。     

Proinflammatory cytokine synthesis by mucosal fibroblasts from mouse colitis is enhanced by interferon-gamma-mediated up-regulation of CD40 signalling

Gut mesenchymal fibroblasts form complex phenotypical and functional populations. They participate actively in homeostatic maintenance of the extracellular matrix, epithelial barrier function, repair mechanisms and leucocyte migration. In inflammation, they become activated, change matrix expression and synthesize proinflammatory mediators. Subpopulations of mucosal fibroblasts express CD40 and the aim of this study was to define its role in their proinflammatory function. Stable primary fibroblast lines derived from normal mouse colon and inflamed colon from CD4(+) CD45RB(high)-transplanted SCID mice were used as models to explore the role of mucosal fibroblast CD40 in the inflammatory process. Phenotype correlated with in situ fibroblast phenotype in the tissues of origin. Lines from both sources co-expressed CD40 and Thy1.2 independently of alpha-smooth muscle actin. A subpopulation of CD40(+) fibroblasts from normal colon expressed CD40 at high levels and expression was enhanced by interferon (IFN)-gamma treatment, whereas all CD40(+) fibroblasts from colitis expressed at low levels and expression was unaffected by IFN-gamma treatment. Despite lower-level expression of CD40 by cells from colitis, they secreted constitutively interleukin (IL)-6 and C-C chemokine (CCL)2. Ligation of CD40 enhanced secretion of these mediators and induced secretion of CCL3. CD40 in cells from colitis was more responsive to ligation than CD40 on cells from normal tissue and this sensitivity was amplified selectively by the action of IFN-gamma. We conclude that the inflammatory milieu in colitis induces long-lasting changes in phenotype and proinflammatory function in colonic fibroblasts. In particular, proinflammatory signalling from fibroblast CD40 is amplified synergistically by the Th1 effector T cell cytokine, IFN-gamma.     

Detection of cell-adhesion molecules on human liver-associated lymphocytes.

Liver-associated lymphocytes (LAL) from human liver are phenotypically and functionally different from peripheral blood lymphocytes (PBL). Phenotypically, they are mainly represented by the CD3+/-CD56+ phenotype and functionally they spontaneously possess lymphokine-activated killer (LAK) activity. In this study we evaluated the expression of cell-adhesion molecules (CAM) which could be involved in LAL contacts with other sinusoidal cells and/or be responsible for the LAK activity. The LAL population was isolated by sinusoidal high-pressure lavage from partial hepatectomies obtained from patients operated on for benign liver disease (n = 6). Surface expression of the beta 2 integrin chains (CD18, CD11a, CD11b, CD11c), as well as that of members of the immunoglobulin superfamily (CD2, CD54, CD56, CD58), were analysed by one or two-colour flow cytometry. Quantitative and qualitative differences were observed in the expression of CAM between LAL and PBL. LAL were characterized by an increase in the percentages of CD11b+, CD54+, CD56+ and CD58+ cells and a decrease in the percentage of CD2+ cells compared to PBL. Fluorescence intensity values for CD2 and CD56 were higher in LAL than in PBL. Moreover, CD11a/CD18 cells presented a bimodal distribution (dim and bright) in both PBL and LAL; whereas these two subpopulations were equally represented in PBL, the number of bright cells was significantly greater (> 80%) in LAL. The increase in CAM expression (percentage of positive cells and intensity of fluorescence) on LAL combined with their increase in natural killer (NK) and LAK activities already reported, support the idea that, at least some, LAL might be, compared to PBL, in an activated state in vivo.     

Cetirizine-induced downregulation of airway fibroblast proliferation and function: a rationale for a different approach to allergy treatment?

Recently, airway fibroblasts captured the attention of both allergists and basic scientists since they are no longer considered as mere bystanders, as far as allergic airway diseases are concerned. The aim of the present study was to assess the effects of different Cetirizine (Cet) concentrations (0.01, 0.05, 0.1 mg/ml) on human airway fibroblast proliferation and on CD54 expression. By means of flow cytometry analysis, we evaluated CD54 expression by airway fibroblasts in basal conditions or after gammaIFN stimulation in the presence of Cetirizine; we also evaluated the effect of the drug on cell proliferation by a [3H]thymidine incorporation assay. All of the tested doses of Cetirizine were able to significantly reduce CD54 upregulation induced by gammaIFN; concerning the fibroblast proliferation, we observed a dose-dependent inhibition of [3H]thymidine incorporation. These results show that Cetirizine exerts a biologic effect directly on human airway fibroblasts, suggesting a new rationale in the use of this compound.     

Analysis of a CD40 ligand dinucleotide microsatellite in multiple sclerosis.

In recent years, numerous reports have described the diverse roles of the CD40-CD40 ligand receptor-ligand pair. The interaction of these two cell-surface molecules regulates both humoral and cell-mediated immune functions. Because the CD40 ligand is known to be highly expressed on the peripheral blood mononuclear cells (PBMC) of multiple sclerosis (MS) patients, and because activated helper T cells expressing CD40 ligand have been found in the brain sections of MS patients, but not in those of normal controls, the protein is believed to be involved in MS development. We studied the influence of a polymorphic dinucleotide-repeat marker located in the 3' untranslated region of the X-linked gene encoding CD40 ligand (CD40LG) on susceptibility to and disease severity in MS. From a total cohort of 771 Nordic definite-MS patients, the most (n = 92) and least (n = 90) disabled octiles, as well as random samples of intermediately disabled males (n = 119) and females (n = 121), were genotyped; 135 ethnically matched healthy subjects were used as controls. In addition, the effect of the polymorphism on CD40 ligand mRNA expression was assessed using PBMC from 54 MS patients and 22 controls. The phenotype frequencies for the CD40LG marker did not differ significantly between gender-conditioned intermediate-MS subgroups and controls, or between gender-conditioned disability octiles. Nor did the polymorphism appear to exert any significant effect on mRNA expression in either patients or controls.     

Fibroblast subsets in the human orbit: Thy-1+ and Thy-1- subpopulations exhibit distinct phenotypes

An emerging concept is that fibroblasts are not homogeneous, but rather consist of subsets, capable of producing regulatory mediators that control regional inflammatory responses. Fibroblasts are key effector cells in Graves' ophthalmopathy, responsible for the connective tissue remodeling, and are a rich source of inflammatory mediators. The purpose of this research was to characterize subsets of the fibroblasts in the human orbit. The strategy used was to define fibroblast subpopulations based on surface expression of the Thy-1 antigen. Fibroblast strains derived from human orbital connective tissue exhibit heterogeneous Thy-1 expression. We show, for the first time, separation of orbital fibroblasts into functionally distinct Thy-1+ and Thy-1- subsets using magnetic beading techniques. Both subsets produced the pro-inflammatory cytokine interleukin-6 (IL-6) after stimulation with IL-1beta or the CD40 pathway, whereas Thy-1+ fibroblasts produced higher levels of prostaglandin endoperoxide H synthase-2 (PGHS-2) and prostaglandin E2 (PGE(2)). Thy-1- fibroblasts produced more IL-8 than Thy-1+ fibroblasts, and when treated with interferon-gamma (IFN-gamma) up-regulated MHC class II expression more robustly. Furthermore, CD40 was expressed in a bimodal distribution within each fibroblast subset. These observations suggest that fibroblast subsets in the human orbit play distinct roles in the regulation of immune and inflammatory responses crucial in the initiation and development of thyroid-associated ophthalmopathy.     

Lymphokine-activated killer (LAK) cells: I. Age-dependent decline of LAK cell-mediated cytotoxicity

Experiments were designed to assess age-related changes in generation of lymphokine-activated killer (LAK) cells and to test whether these changes can be modified by diets differing in the proportion of polyunsaturated to saturated fatty acids (P/S). Ficoll-Hypaque-isolated spleen lymphocytes of rodent chow-fed, 6-85-week-old C57BL/6 (H-2b), 8-81-week-old C57BL/10 (H-2b) and 6-62-week-old SJL (H-2s) mice were cultured in IL-2-containing medium and examined in 51Cr cytotoxicity assay. Similarly, Ficoll-Hypaque-isolated spleen lymphocytes of 6-36-week-old SJL mice fed diets which differed in the ratio of polyunsaturated/saturated fatty acids were cultured in IL-2-containing medium and assayed for cytotoxicity. Age-related decline of LAK cell-mediated cytolysis was observed in mice of both H-2b and H-2s haplotype. The age-related decline of LAK cell-mediated cytolysis was the consequence of age-related decrease in the rate of LAK cell precursor maturation. SJL mice fed from birth with diets differing in P/S did not differ in LAK cell-mediated cytolysis.     

Haemorrhage produces depressions in alloantigen-specific immune responses in the mouse through activation of suppressor T cells.

The development of cell-mediated and humoral immune responses in BALB/c mice (H-2d) directed toward El4 cells (H-2b) was suppressed (cell-mediated cytotoxicity, 40-50% of control; antibody titres 127 +/- 17 versus 287 +/- 17 in controls) following haemorrhage of 30% total blood volume. This haemorrhage-induced depression of immune response can be transferred to normal recipients with T cells (3 x 10(7] from haemorrhaged syngeneic donors. Flow microfluorimetry (FMF) analysis showed no shift in CD8:CD4 ratios following haemorrhage. These results suggest that haemorrhage suppresses immune response through activation of suppressor T cells.     

Association of T cell and macrophage dysfunction with surface gp 120-immunoglobulin-complement complexes in HIV-infected patients.

The mechanism of CD4+ cell depletion and functional T helper cell inhibition in HIV-infected individuals is poorly understood. The present study demonstrates that immune complex-covered CD4+ cells are associated with T cell inhibition and macrophage stimulation. We studied 30 patients with ARC/AIDS and 35 asymptomatic HIV+ haemophilia patients. Overall, 20 +/- 3% of peripheral CD4+ lymphocytes were covered with gp120 (range 0-94%). gp120+ cells also exhibited surface-bound IgG (P = 0.0001), IgM (P = 0.0001), and complement (P = 0.0001). Decreased in vitro lymphocyte proliferation was associated with the immune complex load of CD4+ cells. The higher the percentage of CD4+ gp 120+ cells in the blood, the lower the T cell response in vitro (P = 0.001). Moreover, an association was found between immune complex-positive cells and plasma neopterin (P = 0.01). Patients with increased plasma neopterin levels had decreased in vitro responses to pokeweed mitogen (PWM) (P = 0.006), phytohaemagglutinin (PHA) (P = 0.004), concanavalin A (Con A) (P = 0.09), and anti-CD3 MoAb (P = 0.03), and decreased CD4+ cell counts in the blood (P = 0.006). Since maximally 1% of CD4+ lymphocytes are infected with HIV, T cell dysfunction and T cell depletion in HIV-infected patients may also be caused by the release of free gp120 that binds to uninfected CD4+ cells. Our data suggest that the functional inhibition and subsequent elimination of uninfected CD4+ lymphocytes with surface gp120-immunoglobulin-complement complexes may be a pathomechanism in the manifestation of AIDS.     

Defective interleukin-2 induction of lymphokine-activated killer (LAK) activity in peripheral blood T lymphocytes of patients with monoclonal gammopathies.

The recombinant interleukin-2 (rIL-2) generation of lymphokine-activated killer (LAK) cells was investigated in peripheral blood T lymphocytes (PBT) of 16 patients with monoclonal gammopathy of undetermined significance (MGUS) and 32 patients with multiple myeloma (MM). LAK activity was significantly decreased in MM, but not in MGUS patients, and was partially recovered in MM in the remission phase. This finding was unexpected, because CD8+ CD11b+ cells, which contain LAK precursors, are significantly increased in MM. LAK activity was investigated in purified CD8+ CD11b+ lymphocytes to discriminate between an intrinsic defect or a defective regulation by other T cell subsets. These cells were intrinsically unable to generate LAK activity fully following rIL-2 stimulation. MM showed the more pronounced LAK deficiency, while MGUS patients showed intermediate values. Phenotyping revealed significantly increased proportions of Leu7+ and HLA-DR+ cells in MM patients. These data reveal another dysregulation of T cell effector functions in patients with monoclonal gammopathies and offer further evidence of the impairment of their cell-mediated immunity.     

人脐带间充质干细胞体外诱导分化为成纤维细胞

背景：脐带间充质干细胞具有多向分化能力,但其向成纤维细胞分化研究较少。 目的：验证人脐带间充质干细胞向成纤维细胞的分化能力。 方法：采用贴壁法分离脐带间充质干细胞,流式细胞仪分析其表面抗原。取第3代脐带间充质干细胞进行成脂成骨诱导分化,以碱性成纤维细胞生长因子诱导脐带间充质干细胞向成纤维细胞分化。 结果与结论：贴壁法能稳定从脐带中分离出干细胞,脐带间充质干细胞极低表达 CD31、CD45 、CD40、HLA-DR,强表达 CD29、CD90、CD44、CD105。脐带间充质干细胞成脂诱导后油红O染色显示胞浆中充满红色的油滴;成骨诱导后茜素红染色可在细胞密集区见红色的钙结节。碱性成纤维细胞生因子诱导后细胞表达Ⅰ型胶原明显高于对照组。提示贴壁法分离脐带间充质干细胞可靠、纯度高,碱性成纤维细胞生长因子可诱导脐带间充质干细胞向成纤维细胞分化。中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程全文链接：     

Tolerogenic effect of mouse fibroblasts on dendritic cells

There is controversy about the immunomodulatory effect of fibroblasts on dendritic cells (DCs). To clarify this issue, in this study, we have evaluated different features of fibroblast‐primed DCs including their ability to express co‐inhibitory and co‐stimulatory molecules, pro‐inflammatory and anti‐inflammatory cytokines and their ability to induce T‐cell proliferation. We also examined migratory capacity of DCs to lymphatic tissues and present fibroblast‐derived antigens after encountering fibroblasts. The results of our in vitro study showed that both co‐inhibitory (programmed death ligand 1 and ligand 2 and B7H4) and co‐stimulatory (CD86) molecules were up‐regulated when DCs were co‐cultured with fibroblasts. In an animal model, we showed that intra‐ peritoneal injection (IP) of both syngeneic and allogeneic fibroblasts significantly increased both total DC count and expression level of co‐inhibitory and co‐stimulatory molecules on DCs. Priming of DCs with syngeneic and allogeneic fibroblasts reduced the proliferation of CD4⁺ and CD8⁺ T cells. Even activation of fibroblast‐ primed DCs failed to restore their ability to induce T‐cell proliferation. Likewise, priming of DCs with fibroblasts blocked the ability of ovalbumin‐pulsed DCs to induce proliferation of ovalbumin‐specific CD4⁺ T cells. Compared with non‐activated DCs, fibroblast‐primed DCs had significantly higher expression levels of interleukin‐10 and indoleamine 2, 3 dioxygenase. Fibroblast‐primed DCs had a significantly reduced interleukin‐12 expression level compared with that of activated DCs. After priming with fibroblasts, DCs were able to migrate to lymphatic tissues and present fibroblast‐derived antigens (ovalbumin). In conclusion, after priming with fibroblasts, DCs gain tolerogenic features. This finding suggests the potential role of fibroblasts in the maintenance of immune tolerance.     

Reduced cytokine-mediated up-regulation of HLA-DR in TAP-deficient fibroblasts

Human deficiency in transporter associated with antigen processing (TAP) is characterized by a very low surface expression of human leukocyte antigen (HLA) class I molecules in hematopoietic and non hematopoietic cells. Among the latter, TAP-deficient skin fibroblasts have previously been shown by us to be very sensitive to lysis by activated autologous NK cells, even in the presence of cytokines that up-regulate HLA class I expression, a mechanism sufficient to protect normal fibroblasts from NK cell-mediated killing. Our complementary investigations on two TAP-deficient skin fibroblast cell lines surprisingly revealed that in response to proinflammatory cytokines, up-regulation of HLA-DR molecules at the cell surface is much less marked than in the case of normal skin fibroblasts. In contrast, the surface molecules CD40 and CD54 increase as much as observed on normal cells, suggesting that TAP-deficient fibroblasts are able to efficiently transduce cytokine-mediated stimulating signals. Transfection of an intact TAP gene into one of the TAP-deficient fibroblast cell lines restored a normal HLA class I expression that strongly increased upon IFN-gamma-mediated stimulation, whereas HLA-DR still remained lower than in control cells. These results suggest that, in addition to the defect in the HLA class I antigen presentation pathway, HLA-DR up-regulation is affected in TAP-deficient skin fibroblasts through an unknown mechanism probably independent from TAP.     

The Cd40 ligand

For several years, the primary function of CD40 ligand (CD40L) has been believed to be in regulation of contact-dependent, CD40-CD40L-mediated signals between B-and T-cells, which are essential for the regulation of thymus-dependent (TD) humoral immune responses. Recently, a flurry of reports indicate that CD40 is expressed by variety of cell types other than B-cells that include dendritic cells, follicular dendritic cells, monocytes, macrophages, fibroblasts, and endothelial cells. These studies show that CD40-CD40L interactions are important in inflammatory process. For the past few years, through the availability of CD40L-knockout mice, new data have emerged to support the belief that CD40L has many more functions than its role in TD humoral immunity. CD40L-deficient mice have provided significant information towards our understanding of the in vivo role of CD40L. The current picture that emerges indicates that CD40-CD40L interactions mediate many cell-mediated immune responses and T-cell-mediated effector functions that are required for proper functioning of the host defense system. This article focuses on the in vivo role of the CD40L in regulation of cell-mediated effector functions.