Reactivation of latent tuberculosis infection in TNF-deficient mice

TNF-deficient mice are highly susceptible to Mycobacterium tuberculosis H37Rv infection. Here we asked whether TNF is required for postinfectious immunity in aerosol-infected mice. Chemotherapy for 4 wk commencing 2 wk postinfection reduced CFU to undetectable levels. While wild-type mice had a slight rise in CFU, but controlled infection upon cessation of chemotherapy, TNF-deficient mice developed reactivation of infection with high bacterial loads in lungs, spleen, and liver, which was fatal within 13-18 wk. The increased susceptibility of TNF-deficient mice was accompanied by diminished recruitment and activation of T cells and macrophages into the lung, with defective granuloma formation and reduced inducible NO synthase expression. Reduced chemokine production in the lung might explain suboptimal recruitment and activation of T cells and uncontrolled infection. Therefore, despite a massive reduction of the mycobacterial load by chemotherapy, TNF-deficient mice were unable to compensate and mount a protective immune response. In conclusion, endogenous TNF is critical to maintain latent tuberculosis infection, and in its absence no specific immunity is generated.     

TNF regulates chemokine induction essential for cell recruitment, granuloma formation, and clearance of mycobacterial infection

Host immunity to mycobacterial infection is dependent on the activation of T lymphocytes and their recruitment with monocytes to form granulomas. These discrete foci of activated macrophages and lymphocytes provide a microenvironment for containing the infection. The cytokine, TNF, is essential for the formation and maintenance of granulomas, but the mechanisms by which TNF regulates these processes are unclear. We have compared the responses of TNF-deficient (TNF(-/-)) and wild-type C57BL/6 mice to infection with Mycobacterium smegmatis, a potent inducer of TNF, and virulent Mycobacterium tuberculosis to delineate the TNF-dependent and -independent components of the process. The initial clearance of M. smegmatis was TNF independent, but TNF was required for the early expression of mRNA encoding C-C and C-X-C chemokines and the initial recruitment of CD11b(+) macrophages and CD4(+) T cells to the liver during the second week of infection. Late chemokine expression and cell recruitment developed in TNF(-/-) mice associated with enhanced Th1-like T cell responses and mycobacterial clearance, but recruited leukocytes did not form tight granulomas. Infection of TNF(-/-) mice with M. tuberculosis also resulted in an initial delay in chemokine induction and cellular recruitment to the liver. Subsequently, increased mRNA expression was evident in TNF(-/-) mice, but the loosely associated lymphocytes and macrophages failed to form granulomas and prevent progressive infection. Therefore, TNF orchestrates early induction of chemokines and initial leukocyte recruitment, but has an additional role in the aggregation of leukocytes into functional granulomas capable of controlling virulent mycobacterial infection.     

Structural deficiencies in granuloma formation in TNF gene-targeted mice underlie the heightened susceptibility to aerosol Mycobacterium tuberculosis infection, which is not compensated for by lymphotoxin

TNF and lymphotoxin-alpha (LT alpha) may act at various stages of the host response to Mycobacterium tuberculosis. To dissect the effects of TNF independent of LT alpha, we have used C57BL/6 mice with a disruption of the TNF gene alone (TNF-/-). Twenty-one days following aerosol M. tuberculosis infection there was a marked increase in the number of organisms in the lungs of TNF-/- mice, and by 28-35 days all animals had succumbed, with widespread dissemination of M. tuberculosis. In comparison with the localized granulomas containing activated macrophages and T cells in lungs and livers of C57BL/6 wild-type (wt) mice, cellular infiltrates in TNF-/- mice were poorly formed, with extensive regions of necrosis and neutrophilic infiltration of the alveoli. Phenotypic analysis of lung homogenates demonstrated similar numbers of CD4+ and CD8+ T cells in TNF-/- and wt mice, but in TNF-deficient mice the lymphocytes were restricted to perivascular and peribronchial areas rather than colocated with macrophages in granulomas. T cells from TNF-/- mice retained proliferative and cytokine responses to purified protein derivative, and delayed-type hypersensitivity to purified protein derivative was demonstrable. Macrophages within the lungs of TNF-/- and wt mice showed similar levels of MHC class II and inducible nitric oxide synthase expression, and levels of serum nitrite were comparable. Thus, the enhanced susceptibility of TNF-/- is not compensated for by the presence of LT alpha, and the critical role of TNF is not in the activation of T cells and macrophages but in the local organization of granulomas.     

Neutralization of the chemokine CXCL10 reduces inflammatory cell invasion and demyelination and improves neurological function in a viral model of multiple sclerosis

Intracerebral infection of mice with mouse hepatitis virus (MHV) results in an acute encephalomyelitis followed by a chronic demyelinating disease with clinical and histological similarities with the human demyelinating disease multiple sclerosis (MS). Following MHV infection, chemokines including CXC chemokine ligand (CXCL)10 (IFN inducible protein 10 kDa), CXCL9 (monokine induced by IFN-gamma), and CC chemokine ligand 5 (RANTES) are expressed during both acute and chronic stages of disease suggesting a role for these molecules in disease exacerbation. Previous studies have shown that during the acute phase of infection, T lymphocytes are recruited into the CNS by the chemokines CXCL10 and CXCL9. In the present study, MHV-infected mice with established demyelination were treated with antisera against these two chemokines, and disease severity was assessed. Treatment with anti-CXCL10 reduced CD4+ T lymphocyte and macrophage invasion, diminished expression of IFN-gamma and CC chemokine ligand 5, inhibited progression of demyelination, and increased remyelination. Anti-CXCL10 treatment also resulted in an impediment of clinical disease progression that was characterized by a dramatic improvement in neurological function. Treatment with antisera against CXCL9 was without effect, demonstrating a critical role for CXCL10 in inflammatory demyelination in this model. These findings document a novel therapeutic strategy using Ab-mediated neutralization of a key chemokine as a possible treatment for chronic human inflammatory demyelinating diseases such as MS.     

Characterization of the deregulated immune activation occurring at late stages of mycobacterial infection in TNF-deficient mice

In the absence of TNF, mice infected with Mycobacterium avium suffer a peculiar disintegration of the granulomas, with extensive apoptosis and necrosis of their cells, occurring during the course of the infection and leading to the death of the animals within a few days of its onset. The survival time depends on the virulence of the infecting strain as well as on the dose and route of infection. Intravenously infected mice developed the typical lesions in hepatic granulomas whereas aerosol-infected animals developed them in the lung granulomas. At the onset of the development of pulmonary granuloma disintegration, extensive expansion of T cells, with intense up-regulation of activation markers, massive exacerbation of their ability to secrete IFN-gamma, and increased cytotoxic activity of both CD4(+) and CD8(+) T cells were observed. Forced expression of Bcl2 did not prevent the early death of infected TNF-deficient mice leading merely to a modest increase in survival times. The expression of the FasL on T cells was not affected but there was an intense up-regulation of the TRAIL in T cells and, in particular, myeloid cells. We thus show that an exacerbated immune response occurs in TNF-deficient hosts during M. avium infections that leads to enhanced IFN-gamma production and late up-regulation of TRAIL which may contribute to granuloma disintegration.     

Duffy antigen facilitates movement of chemokine across the endothelium in vitro and promotes neutrophil transmigration in vitro and in vivo

The Duffy Ag expressed on RBCs, capillaries, and postcapillary venular endothelial cells binds selective CXC and CC chemokines with high affinity. Cells transfected with the Duffy Ag internalize but do not degrade chemokine ligand. It has been proposed that Duffy Ag transports chemokines across the endothelium. We hypothesized that Duffy Ag participates in the movement of chemokines across the endothelium and, by doing so, modifies neutrophil transmigration. We found that the Duffy Ag transfected into human endothelial cells facilitates movement of the radiolabeled CXC chemokine, growth related oncogene-alpha/CXC chemokine ligand 1 (GRO-alpha/CXCL1), across an endothelial monolayer. In addition, neutrophil migration toward GRO-alpha/CXCL1 and IL-8 (IL-8/CXCL8) was enhanced across an endothelial monolayer expressing the Duffy Ag. Furthermore, GRO-alpha/CXCL1 stimulation of endothelial cells expressing the Duffy Ag did not affect gene expression by oligonucleotide microarray analysis. These in vitro observations are supported by the finding that IL-8/CXCL8-driven neutrophil recruitment into the lungs was markedly attenuated in transgenic mice lacking the Duffy Ag. We conclude that Duffy Ag has a role in enhancing leukocyte recruitment to sites of inflammation by facilitating movement of chemokines across the endothelium.     

Critical role for CXCR3 chemokine biology in the pathogenesis of bronchiolitis obliterans syndrome

Bronchiolitis obliterans syndrome (BOS) is the major limitation to survival post-lung transplantation and is characterized by a persistent peribronchiolar inflammation that eventually gives way to airway fibrosis/obliteration. Acute rejection is the main risk factor for the development of BOS and is characterized by a perivascular/bronchiolar leukocyte infiltration. The specific mechanism(s) by which these leukocytes are recruited have not been elucidated. The CXC chemokines (monokine induced by IFN-gamma (MIG)/CXC chemokine ligand (CXCL)9, IP-10/CXCL10, and IFN-inducible T cell alpha chemoattractant (ITAC)/CXCL11) act through their shared receptor, CXCR3. Because they are potent leukocyte chemoattractants and are involved in other inflammation/fibroproliferative diseases, we hypothesized that the expression of these chemokines during an allogeneic response promotes the persistent recruitment of mononuclear cells, leading to chronic lung rejection. We found that elevated levels of MIG/CXCL9, IFN-inducible protein 10 (IP-10)/CXCL10, and ITAC/CXCL11 in human bronchoalveolar lavage fluid were associated with the continuum from acute to chronic rejection. Translational studies in a murine model demonstrated increased expression of MIG/CXCL9, IP-10/CXCL10, and ITAC/CXCL11 paralleling the recruitment of CXCR3-expressing mononuclear cells. In vivo neutralization of CXCR3 or its ligands MIG/CXCL9 and IP-10/CXCL10 decreased intragraft recruitment of CXCR3-expressing mononuclear cells and attenuated BOS. This supports the notion that ligand/CXCR3 biology plays an important role in the recruitment of mononuclear cells, a pivotal event in the pathogenesis of BOS.     

Expression cloning of the STRL33/BONZO/TYMSTRligand reveals elements of CC, CXC, and CX3C chemokines

STRL33/BONZO/TYMSTR is an orphan chemokine and HIV/SIV coreceptor receptor that is expressed on activated T lymphocytes. We describe an expression cloning strategy whereby we isolated a novel chemokine, which we name CXCL16. CXCL16 is an alpha (CXC) chemokine but also has characteristics of CC chemokines and a structure similar to fractalkine (neurotactin) in having a transmembrane region and a chemokine domain suspended by a mucin-like stalk. A recombinant version of CXCL16 fails to mediate chemotaxis to all known chemokine receptor transfectants tested but does mediate robust chemotaxis, high affinity binding, and calcium mobilization to Bonzo receptor transfectants, indicating that this is a unique receptor ligand interaction. In vitro polarized T cell subsets including Th1, Th2, and Tr1 cells express functional Bonzo, suggesting expression of this receptor in chronic inflammation, which we further verified by demonstration of CXCL16-mediated migration of tonsil-derived CD4(+) T lymphocytes. CXCL16 is expressed on the surface of APCs including subsets of CD19(+) B cells and CD14(+) monocyte/macrophages, and functional CXCL16 is also shed from macrophages. The combination of unique structural features of both Bonzo and CXCL16 suggest that this interaction may represent a new class of ligands for this receptor family. Additionally, this chemokine might play a unique dual role of attracting activated lymphocyte subsets during inflammation as well as facilitating immune responses via cell-cell contact.     

CD4+ T cell migration into the cornea is reduced in CXCL9 deficient but not CXCL10 deficient mice following herpes simplex virus type 1 infection

The role of CXCL9 and CXCL10 in the ocular immune response to herpes simplex virus type 1 (HSV-1) infection was investigated using mice deficient in either CXCL9 or CXCL10. CXCL10 but not CXCL9 deficient mice showed an increase in sensitivity to ocular virus infection as measured by an elevation in virus titer recovered in the tear film and corneal tissue. The increase in virus was associated with an increase in the expression of the chemokine CCL2 but no significant change in the infiltration of CD4(+) T cells or NK cells into the corneal stroma. In contrast, a significant reduction in CD4(+) T cell infiltration into the cornea was found in CXCL9 deficient mice following HSV-1 infection consistent with the absence of CXCL9 expression and reduction in expression of other chemokines including CCL3, CCL5, CXCL1, and CXCL10. Collectively, the results suggest a non-redundant role for CXCL9 and CXCL10 in response to ocular HSV-1 infection in terms of controlling virus replication and recruitment of CD4(+) T cells into the cornea.     

Chemokines and tuberculosis

Mycobacterium tuberculosis is a respiratory pathogen responsible for tuberculosis. A primary pathologic feature of M. tuberculosis infection is the formation of a granuloma. Immune cells migrate to the lung and then through the lung to the site of infection to form a granuloma. This structure contains the infection, and is often maintained for a long period of time. The signals responsible for granuloma formation and maintenance are largely unknown. Since chemokines and chemokine receptors direct cells to specific sites within the tissues, it is plausible that these cells participate in granuloma formation. In this review, the current literature on chemokines and M. tuberculosis infection, as well as the specific role that tumor necrosis factor alpha (TNF-) plays in granuloma formation and chemokine expression are discussed.     

CXCR3 and its ligands in a murine model of obliterative bronchiolitis: regulation and function

Lung transplantation remains the only effective therapy for patients with end-stage lung disease, but survival is limited by the development of obliterative bronchiolitis (OB). The chemokine receptor CXCR3 and two of its ligands, CXCL9 and CXCL10, have been identified as important mediators of OB. However, the relative contribution of CXCL9 and CXCL10 to the development of OB and the mechanism of regulation of these chemokines has not been well defined. In this study, we demonstrate that CXCL9 and CXCL10 are up-regulated in unique patterns following tracheal transplantation in mice. In these experiments, CXCL9 expression peaked 7 days posttransplant, while CXCL10 expression peaked at 1 day and then again 7 days posttransplant. Expression of CXCL10 was also up-regulated in a novel murine model of lung ischemia, and in bronchoalveolar lavage fluid taken from human lungs 24 h after lung transplantation. In further analysis, we found that 3 h after transplantation CXCL10 is donor tissue derived and not dependent on IFN-gamma or STAT1, while 24 h after transplantation CXCL10 is from recipient tissue and regulated by IFN-gamma and STAT1. Expression of both CXCL9 and CXCL10 7 days posttransplant is regulated by IFN-gamma and STAT1. Finally, we demonstrate that deletion of CXCR3 in recipients reduces airway obliteration. However, deletion of either CXCL9 or CXCL10 did not affect airway obliteration. These data show that in this murine model of obliterative bronchiolitis, these chemokines are differentially regulated following transplantation, and that deletion of either chemokine alone does not affect the development of airway obliteration.     

Pleiotropic functions of the CXC-type chemokine CXCL14 in mammals

CXCL14 is a member of the CXC chemokine family. CXCL14 possesses chemoattractive activity for activated macrophages, immature dendritic cells and natural killer cells. CXCL14-deficient mice do not exhibit clear immune system abnormalities, suggesting that the function of CXCL14 can be compensated for by other chemokines. However, CXCL14 does appear to have unique biological roles. It suppresses the in vivo growth of lung and head-and-neck carcinoma cells, whereas the invasiveness of breast and prostate cancer cells appears to be promoted by CXCL14. Moreover, recent evidence revealed that CXCL14 participates in glucose metabolism, feeding behaviour-associated neuronal circuits, and anti-microbial defense. Based on the expression patterns of CXCL14 and CXCL12 during embryonic development and in the perinatal brain in mice, the functions of these two chemokines may be opposite or interactive. Although CXCL14 receptors have not yet been identified, the intracellular activity of CXCL14 in breast cancer cells suggests that the CXCL14 receptor(s) and signal transduction pathway(s) may be different from those of conventional CXC-type chemokines.     

Chemokines regulate small leucine-rich proteoglycans in the extracellular matrix of the pressure-overloaded right ventricle

Chemokines have been suggested to play a role during development of left ventricular failure, but little is known about their role during right ventricular (RV) remodeling and dysfunction. We have previously shown that the chemokine (C-X-C motif) ligand 13 (CXCL13) regulates small leucine-rich proteoglycans (SLRPs). We hypothesized that chemokines are upregulated in the pressure-overloaded RV, and that they regulate SLRPs. Mice with RV pressure overload following pulmonary banding (PB) had a significant increase in RV weight and an increase in liver weight after 1 wk. Microarray analysis (Affymetrix) of RV tissue from mice with PB revealed that CXCL10, CXCL6, chemokine (C-X3-C motif) ligand 1 (CX3CL1), chemokine (C-C motif) ligand 5 (CCL5), CXCL16, and CCL2 were the most upregulated chemokines. Stimulation of cardiac fibroblasts with these same chemokines showed that CXCL16 increased the expression of the four SLRPs: decorin, lumican, biglycan, and fibromodulin. CCL5 increased the same SLRPs, except decorin, whereas CX3CL1 increased the expression of decorin and lumican. CXCL16, CX3CL1, and CCL5 were also shown to increase the levels of glycosylated decorin and lumican in the medium after stimulation of fibroblasts. In the pressure-overloaded RV tissue, Western blotting revealed an increase in the total protein level of lumican and a glycosylated form of decorin with a higher molecular weight compared with control mice. Both mice with PB and patients with pulmonary stenosis had significantly increased circulating levels of CXCL16 compared with healthy controls measured by enzyme immunoassay. In conclusion, we have found that chemokines are upregulated in the pressure-overloaded RV and that CXCL16, CX3CL1, and CCL5 regulate expression and posttranslational modifications of SLRPs in cardiac fibroblasts. In the pressure-overloaded RV, protein levels of lumican were increased, and a glycosylated form of decorin with a high molecular weight appeared.     

Outer membrane protein A from Klebsiella pneumoniae activates bronchial epithelial cells: implication in neutrophil recruitment

Aside from its mechanical barrier function, bronchial epithelium plays an important role both in the host defense and in the pathogenesis of inflammatory airway disorders. To investigate its role in lung defense, the effect of a bacterial cell wall protein, the outer membrane protein A from Klebsiella pneumoniae (kpOmpA) on bronchial epithelial cells (BEC) was evaluated on adhesion molecule expression and cytokine production. Moreover, the potential implication of this mechanism in kpOmpA-induced lung inflammation was also determined. Our in vitro studies demonstrated that kpOmpA strongly bound to BEAS-2B cells, a human BEC line, and to BEC primary cultures, resulting in NF-kappaB signaling pathway activation. Exposure to kpOmpA increased ICAM-1 mRNA and cell surface expression, as well as the secretion of IL-6, CXC chemokine ligand (CXCL)1, CXCL8, C-C chemokine ligand 2, CXCL10 by BEAS-2B cells, and BEC primary cultures (p < 0.005). We analyzed in vivo the consequences of intratracheal injection of kpOmpA to BALB/c mice. In kpOmpA-treated mice, a transient neutrophilia (with a maximum at 24 h) was observed in bronchoalveolar lavage and lung sections. In vivo kpOmpA priming induced bronchial epithelium activation as evaluated by ICAM-1 and CXCL1 expression, associated with the secretion of CXCL1 and CXCL5 in bronchoalveolar lavage fluids. In the lung, an increased level of the IL-6, CXCL1, CXCL5, CXCL10 mRNA was observed with a maximum at 6 h. These data showed that kpOmpA is involved in host defense mechanism by its ability to activate not only APC but also BEC, resulting in a lung neutrophilia.     

Chemokines determine local lymphoneogenesis and a reduction of circulating CXCR4+ T and CCR7 B and T lymphocytes in thyroid autoimmune diseases

Chemokines and their corresponding receptors are crucial for the recruitment of lymphocytes into the lymphoid organs and for its organization acting in a multistep process. Tissues affected by autoimmune disease often contain ectopic lymphoid follicles which, in the case of autoimmune thyroid disorders, are highly active and specific for thyroid Ags although its pathogenic role remains unclear. To understand the genesis of these lymphoid follicles, the expression of relevant cytokines and chemokines was assessed by real time PCR, immunohistochemistry and by in vitro assays in autoimmune and nonautoimmune thyroid glands. Lymphotoxin alpha, lymphotoxin beta, C-C chemokine ligand (CCL) 21, CXC chemokine ligand (CXCL) 12, CXCL13, and CCL22 were increased in thyroids from autoimmune patients, whereas CXCL12, CXCL13, and CCL22 levels were significantly higher in autoimmune glands with ectopic secondary lymphoid follicles than in those without follicles. Interestingly, thyroid epithelium produced CXCL12 in response to proinflammatory cytokines providing a possible clue for the understanding of how tissue stress may lead to ectopic follicle formation. The finding of a correlation between chemokines and thyroid autoantibodies further suggests that intrathyroidal germinal centers play a significant role in the autoimmune response. Unexpectedly, the percentage of circulating CXCR4(+) T cells and CCR7(+) B and T cells (but not of CXCR5) was significantly reduced in PBMCs of patients with autoimmune thyroid disease when they were compared with their intrathyroidal lymphocytes. This systemic effect of active intrathyroidal lymphoid tissue emerges as a possible new marker of thyroid autoimmune disease activity.     

Transmembrane TNF is sufficient to initiate cell migration and granuloma formation and provide acute, but not long-term, control of Mycobacterium tuberculosis infection

TNF is critical for immunity against Mycobacterium tuberculosis infection; however, the relative contributions of the soluble and transmembrane forms of TNF in this immunity are unknown. Using memTNF mice, which express only the transmembrane form of TNF, we have addressed this question. Wild-type (WT), TNF-/-, and transmembrane TNF (memTNF) mice were infected with M. tuberculosis by aerosol. TNF-/- mice developed overwhelming infection with extensive pulmonary necrosis and died after only 33 days. memTNF mice, like WT mice, contained bacterial growth for over 16 wk, developed an Ag-specific T cell response, and initially displayed compact granulomas, comprised of both lymphocytes and macrophages. Expression of mRNA for the chemokines CXCL10, CCL3, CCL5, and CCL7 was comparable in both WT and memTNF mice. As the infection progressed, however, the pulmonary lesions in memTNF mice became larger and more diffuse, with increased neutrophil accumulation and necrosis. This was accompanied by increased influx of activated memory T cells into the lungs of memTNF mice. Eventually, these mice succumbed to infection with a mean time to death of 170 days. The expression of memTNF on T cells is functionally important because the transfer of T cells from memTNF, but not TNF-/- mice, into either RAG-/- or TNF-/- mice conferred the same survival advantage on the M. tuberculosis-infected recipient mice, as the transfer of WT T cells. Therefore, memTNF, in the absence of soluble TNF, is sufficient to control acute, but not chronic, M. tuberculosis infection, in part through its expression on T cells.     

Depletion of alveolar macrophages exerts protective effects in pulmonary tuberculosis in mice

Mycobacterium tuberculosis bacilli are intracellular organisms that reside in phagosomes of alveolar macrophages (AMs). To determine the in vivo role of AM depletion in host defense against M. tuberculosis infection, mice with pulmonary tuberculosis induced by intranasal administration of virulent M. tuberculosis were treated intranasally with either liposome-encapsulated dichloromethylene diphosphonate (AM(-) mice), liposomes, or saline (AM(+) mice). AM(-) mice were completely protected against lethality, which was associated with a reduced outgrowth of mycobacteria in lungs and liver, and a polarized production of type 1 cytokines in lung tissue, and by splenocytes stimulated ex vivo. AM(-) mice displayed deficient granuloma formation, but were more capable of attraction and activation of T cells into the lung and had increased numbers of pulmonary polymorphonuclear cells. These data demonstrate that depletion of AMs is protective during pulmonary tuberculosis.     

Rapid up-regulation of CXC chemokines in the airways after Ag-specific CD4+ T cell activation

Ag-specific activation of CD4(+) T cells is known to be causative for the cytokine production associated with lung allergy. Chemokine-induced leukocyte recruitment potentially represents a critical early event in Ag-induced lung inflammation. Whether Ag-specific, lung CD4(+) T cell activation is important in lung chemokine production is currently not clear. Using alphabeta-TCR transgenic BALB/c DO11.10 mice, we investigated the ability of Ag-specific CD4(+) T cell activation to induce lung chemokine production and leukocyte recruitment. Within 1 h of exposure of DO11. 10 mice to OVA aerosol, lung mRNA and protein for the neutrophil chemokines KC and macrophage inflammatory protein (MIP)-2 were greatly increased. Accordingly, neutrophils in the airways increased by >50-fold, and KC and MIP-2 proved to be functional because their neutralization significantly reduced airway neutrophilia. CD4(+) T cell activation was critical because CD4(+) but not CD8(+) T cell depletion reduced KC production, which correlated well with the previously observed inhibition of neutrophil influx after CD4(+) T cell depletion. In vitro studies confirmed that OVA-induced KC and MIP-2 production was conditional upon the interaction of CD4(+) T cells with APCs. A likely secondary mediator was TNF-alpha, and a probable source of these chemokines in the lung was alveolar macrophages. Thus, Ag-specific CD4(+) T cell activation in the lung leads to rapid up-regulation of neutrophil chemokines and the recruitment of neutrophils to the site of Ag exposure. This may be a key early event in the pathogenesis of Ag-induced lung inflammation.