Development of murine lupus involves the combined genetic contribution of the SLAM and FcgammaR intervals within the Nba2 autoimmune susceptibility locus.

Autoantibodies are of central importance in the pathogenesis of Ab-mediated autoimmune disorders. The murine lupus susceptibility locus Nba2 on chromosome 1 and the syntenic human locus are associated with a loss of immune tolerance that leads to antinuclear Ab production. To identify gene intervals within Nba2 that control the development of autoantibody-producing B cells and to determine the cellular components through which Nba2 genes accomplish this, we generated congenic mice expressing various Nba2 intervals where genes for the FcgammaR, SLAM, and IFN-inducible families are encoded. Analysis of congenic strains demonstrated that the FcgammaR and SLAM intervals independently controlled the severity of autoantibody production and renal disease, yet are both required for lupus susceptibility. Deregulated homeostasis of terminally differentiated B cells was found to be controlled by the FcgammaR interval where FcgammaRIIb-mediated apoptosis of germinal center B cells and plasma cells was impaired. Increased numbers of activated plasmacytoid dendritic cells that were distinctly CD19+ and promoted plasma cell differentiation via the proinflammatory cytokines IL-10 and IFNalpha were linked to the SLAM interval. These findings suggest that SLAM and FcgammaR intervals act cooperatively to influence the clinical course of disease through supporting the differentiation and survival of autoantibody-producing cells.

Selective expansion of regulatory T cells by NKTR-358 in healthy volunteers and patients with systemic lupus erythematosus.

Objective: To evaluate NKTR-358, a polyethylene glycol-interleukin-2 conjugate composition designed to selectively induce regulatory T cells (Tregs), in first-in-human studies. Methods: Healthy volunteers and patients with systemic lupus erythematosus (SLE) received single- or multiple-dose (biweekly) NKTR-358 or placebo in two sequential, randomized, phase 1 studies (single ascending dose [SAD; NCT04133116] and multiple ascending dose [MAD; NCT03556007]). Primary objectives were safety and tolerability; secondary objectives included pharmacokinetics (PK) and immune effects of NKTR-358; exploratory objectives included effects on SLE disease activity. Results: There were eight ascending dose cohorts in the SAD study (0.3-28.0 µg/kg: n = 76; placebo: n = 24) and four in the MAD study (3-24.0 µg/kg: n = 36; placebo: n = 12). Most adverse events (AEs) were grade 1-2 injection-site reactions, with no treatment-related serious or severe AEs, or deaths. PK data showed dose proportionality and prolonged exposure (mean half-life: 7.4-12.9 days). Dose-dependent, selective, and sustained increases in percentages and absolute numbers of total CD4+ Tregs and CD25bright Tregs were observed, with no significant changes in conventional CD4+ and CD8+ T cells, and low-level increases in natural killer cells. At the highest doses tested, administration of NKTR-358 resulted in a 12-17-fold increase in CD25bright Tregs over baseline that was sustained for 20-30 days. Conclusion: NKTR-358 was well tolerated, had a suitable PK profile for biweekly dosing, and led to marked and selective dose-dependent increases in CD25bright Tregs, with no significant changes in conventional T cells. These results provide strong support for further testing in SLE and other inflammatory diseases.

Homeostatically proliferating CD4 T cells are involved in the pathogenesis of an Omenn syndrome murine model.

Patients with Omenn syndrome (OS) have hypomorphic RAG mutations and develop varying manifestations of severe combined immunodeficiency. It is not known which symptoms are caused directly by the RAG mutations and which depend on other polymorphic genes. Our current understanding of OS is limited by the lack of an animal model. In the present study, we identified a C57BL/10 mouse with a spontaneous mutation in, and reduced activity of, RAG1. Mice bred from this animal contained high numbers of memory-phenotype T cells and experienced hepatosplenomegaly and eosinophilia, had oligoclonal T cells, and demonstrated elevated levels of IgE, major symptoms of OS. Depletion of CD4+ T cells in the mice caused a reduction in their IgE levels. Hence these "memory mutant" mice are a model for human OS; many symptoms of their disease were direct results of the Rag hypomorphism and some were caused by malfunctions of their CD4+ T cells.

Critical role of TLR7 in the acceleration of systemic lupus erythematosus in TLR9-deficient mice.

Accumulating evidence supports the idea that TLR7 and TLR9 play pathogenic and protective roles, respectively, in the development of murine systemic lupus erythematosus (SLE). However, the molecular mechanism responsible for the accelerated development of SLE resulting from the deletion of TLR9 and the respective contributions of TLR7 and TLR9 to the development of different autoimmune responses against nuclear and non-nuclear autoantigens implicated in lupus nephritis have not been well defined. In the present study, we addressed these questions by assessing the effect of the TLR9 and/or TLR7 deletion on the production of various autoantibodies and the development of lupus nephritis in C57BL/6 mice congenic for the Nba2 (NZB autoimmunity 2) locus (B6.Nba2). TLR9-deficient B6.Nba2 mice displayed increased production of autoantibodies against nuclear antigens, serum retroviral gp70 and glomerular matrix antigens, and developed a markedly accelerated form of lupus nephritis. Enhanced disease was associated with functionally upregulated expression of TLR7, as documented by an increased TLR7-dependent activation of B cells and plasmacytoid dendritic cells. Notably, disease exacerbation in TLR9-deficient mice was completely suppressed by the deletion of TLR7. Our results indicate that TLR7 has a pivotal role in a wide variety of autoimmune responses against DNA- and RNA-containing nuclear antigens, retroviral gp70 and glomerular matrix antigens implicated in murine SLE, and that enhanced TLR7 activity is critical for the accelerated development of SLE in TLR9-deficient lupus-prone mice.

Evidence for genes in addition to Tlr7 in the Yaa translocation linked with acceleration of systemic lupus erythematosus.

The accelerated development of systemic lupus erythematosus (SLE) in male BXSB mice is associated with the genetic abnormality in its Y chromosome, designated Yaa (Y-linked autoimmune acceleration). Recently, the Yaa mutation was identified to be a translocation from the telomeric end of the X chromosome (containing the gene encoding TLR7) onto the Y chromosome. In the present study, we determined whether the Tlr7 gene duplication is indeed responsible for the Yaa-mediated acceleration of SLE. Analysis of C57BL/6 mice congenic for the Nba2 (NZB autoimmunity 2) locus (B6.Nba2) bearing the Yaa mutation revealed that introduction of the Tlr7 null mutation on the X chromosome significantly reduced serum levels of IgG autoantibodies against DNA and ribonucleoproteins, as well as the incidence of lupus nephritis. However, the protection was not complete, because these mice still developed high titers of anti-chromatin autoantibodies and retroviral gp70-anti-gp70 immune complexes, and severe lupus nephritis, which was not the case in male B6.Nba2 mice lacking the Yaa mutation. Moreover, we found that the Tlr7 gene duplication contributed to the development of monocytosis, but not to the reduction of marginal zone B cells, which both are cellular abnormalities causally linked to the Yaa mutation. Our results indicate that the Yaa-mediated acceleration of SLE as well as various Yaa-linked cellular traits cannot be explained by the Tlr7 gene duplication alone, and suggest additional contributions from other duplicated genes in the translocated X chromosome.

Dissection of genetic mechanisms governing the expression of serum retroviral gp70 implicated in murine lupus nephritis.

The endogenous retroviral envelope glycoprotein, gp70, implicated in murine lupus nephritis is secreted by hepatocytes as an acute phase protein, and it has been thought to be a product of an endogenous xenotropic virus, NZB-X1. However, since endogenous polytropic (PT) and modified polytropic (mPT) viruses encode gp70s that are closely related to xenotropic gp70, these viruses can be additional sources of serum gp70. To better understand the genetic basis of the expression of serum gp70, we analyzed the abundance of xenotropic, PT, or mPT gp70 RNAs in livers and the genomic composition of corresponding proviruses in various strains of mice, including two different Sgp (serum gp70 production) congenic mice. Our results demonstrated that the expression of different viral gp70 RNAs was remarkably heterogeneous among various mouse strains and that the level of serum gp70 production was regulated by multiple structural and regulatory genes. Additionally, a significant contribution of PT and mPT gp70s to serum gp70 was revealed by the detection of PT and mPT, but not xenotropic transcripts in 129 mice, and by a closer correlation of serum levels of gp70 with the abundance of PT and mPT gp70 RNAs than with that of xenotropic gp70 RNA in Sgp3 congenic mice. Furthermore, the injection of lipopolysaccharides selectively up-regulated the expression of xenotropic and mPT gp70 RNAs, but not PT gp70 RNA. Our data indicate that the genetic origin of serum gp70 is more heterogeneous than previously thought, and that distinct retroviral gp70s are differentially regulated in physiological vs inflammatory conditions.

Frequency of beryllium-specific, central memory CD4+ T cells in blood determines proliferative response.

Beryllium exposure can lead to the development of beryllium-specific CD4+ T cells and chronic beryllium disease (CBD), which is characterized by the presence of lung granulomas and a CD4+ T cell alveolitis. Studies have documented the presence of proliferating and cytokine-secreting CD4+ T cells in blood of CBD patients after beryllium stimulation. However, some patients were noted to have cytokine-secreting CD4 T cells in blood in the absence of beryllium-induced proliferation, and overall, the correlation between the 2 types of responses was poor. We hypothesized that the relative proportion of memory T cell subsets determined antigen-specific proliferation. In most CBD patients, the majority of beryllium-specific CD4+ T cells in blood expressed an effector memory T cell maturation phenotype. However, the ability of blood cells to proliferate in the presence of beryllium strongly correlated with the fraction expressing a central memory T cell phenotype. In addition, we found a direct correlation between the percentage of beryllium-specific CD4+ T(EM) cells in blood and T cell lymphocytosis in the lung. Together, these findings indicate that the functional capability of antigen-specific CD4+ T cells is determined by the relative proportion of memory T cell subsets, which may reflect internal organ involvement.

CD28 costimulation independence of target organ versus circulating memory antigen-specific CD4+ T cells.

T cell receptor engagement with CD28 costimulation is generally required for naive T cell activation, whereas reactivation of memory cells is less dependent on CD28 costimulation. We studied this process in chronic beryllium disease, in which the frequency of antigen-specific CD4+ T cells in the lung is large and circulating antigen-specific cells are also detectable. In the lung, a large fraction of CD4+ T cells stopped expressing CD28 mRNA and protein, and this change in phenotype correlated with lung inflammation. In the presence of concentrations of CTLA-4Ig that inhibited the CD28-B7 interaction, beryllium-specific CD4+ T cells in lung were still able to proliferate and secrete IFN-gamma in response to beryllium in culture. This functional independence of CD28 costimulation included lung CD28+ effector cells. Although lung CD4+CD28- cells retained the ability to secrete Th1-type cytokines in response to beryllium, they showed less proliferative capacity and were more susceptible to cell death compared with CD28+ T cells. In contrast to lung cells, inhibition of the CD28-B7 interaction markedly reduced responses of beryllium-specific T cells in blood. Taken together, these findings suggest transition within memory CD4+ T cells from CD28 dependence in central memory cells to functional independence and then loss of CD28 expression in effector cells.

Target organ localization of memory CD4(+) T cells in patients with chronic beryllium disease.

Chronic beryllium disease (CBD) is caused by exposure to beryllium in the workplace, and it remains an important public health concern. Evidence suggests that CD4(+) T cells play a critical role in the development of this disease. Using intracellular cytokine staining, we found that the frequency of beryllium-specific CD4(+) T cells in the lungs (bronchoalveolar lavage) of 12 CBD patients ranged from 1.4% to 29% (mean 17.8%), and these T cells expressed a Th1-type phenotype in response to beryllium sulfate (BeSO(4)). Few, if any, beryllium-specific CD8(+) T cells were identified. In contrast, the frequency of beryllium-responsive CD4(+) T cells in the blood of these subjects ranged from undetectable to 1 in 500. No correlation was observed between the frequency of beryllium-responsive bronchoalveolar lavage (BAL) CD4(+) T cells as detected by intracellular staining and lymphocyte proliferation in culture after BeSO(4) exposure. Staining for surface marker expression showed that nearly all BAL T cells exhibit an effector memory cell phenotype. These results demonstrate a dramatically high frequency and compartmentalization of antigen-specific effector memory CD4(+) cells in the lungs of CBD patients. These studies provide insight into the phenotypic and functional characteristics of antigen-specific T cells invading other inaccessible target organs in human disease.

New insights into disease pathogenesis from mouse lupus genetics.

Full manifestation of mouse lupus, similar to the human disease in its severe form, is characterized by elevated antinuclear autoantibody levels and the development of kidney disease. Considerable evidence supports a genetic basis for lupus. The functional dissection of susceptibility loci in multigenic mouse models of lupus has provided insight into the immune abnormalities associated with autoantibody production and other processes critical for inflammation and damage in the kidney. The elucidation of models with single-gene manipulations has also identified immune mechanisms in the pathway to lupus. Recent advances have challenged previously accepted truths and new layers of complexity have become apparent.

Safety, pharmacokinetics and pharmacodynamics of AMG 811, an anti-interferon-γ monoclonal antibody, in SLE subjects without or with lupus nephritis.

OBJECTIVE: To evaluate safety, pharmacokinetics and pharmacodynamics of anti-interferon (IFN)-γ monoclonal antibody AMG 811 in subjects with SLE without or with lupus nephritis (LN). METHODS: In this phase Ib, randomised, multiple-dose escalation study (NCT00818948), subjects without LN were randomised to subcutaneous AMG 811 (6, 20 or 60 mg) or placebo and subjects with LN were randomised to subcutaneous AMG 811 (20, 60 or 120 mg) or placebo every four weeks for three total doses. Outcomes included incidence of adverse events (AEs); pharmacokinetics; levels of serum proteins (CXCL-10, interleukin 18, monocyte chemotactic protein-1); changes in gene transcript profiles and clinical parameters (Safety of Estrogen in Lupus Erythematosus National Assessment-Systemic Lupus Erythematosus Disease Activity Index (SELENA-SLEDAI) scores, proteinuria, anti-double-stranded DNA (anti-dsDNA) antibodies, C3 complement, C4 complement). RESULTS: Fifty-six subjects enrolled (28 SLE without LN; 28 with LN). Baseline mean SELENA-SLEDAI scores were 2.2 and 12.0 for SLE subjects without and with LN, respectively. Most subjects reported an AE; no meaningful imbalances were observed between AMG 811 and placebo. Pharmacokinetic profiles were similar and mostly dose-proportional in subjects without or with LN. AMG 811 treatment reduced CXCL-10 protein levels and blood-based RNA IFN-γ Blockade Signature compared with placebo. Reductions were less pronounced and not sustained in subjects with LN, even at the highest dose tested, compared with subjects without LN. No effect on SELENA-SLEDAI scores, proteinuria, C3 or C4 complement levels, or anti-dsDNA antibodies was observed. CONCLUSION: AMG 811 demonstrated favourable pharmacokinetics and acceptable safety profile but no evidence of clinical impact. IFN-γ-associated biomarkers decreased with AMG 811; effects were less pronounced and not sustained in LN subjects. TRIAL REGISTRATION NUMBER: NCT00818948; results.

The role of B cells in the pathogenesis of rheumatoid arthritis.

The classical paradigm for rheumatoid arthritis (RA) pathogenesis holds that CD4+ T cells mediate joint damage both directly and by driving non-T effector cells to release inflammatory cytokines. By contrast, the new paradigm that is developing centers on an interaction of CD4+ T cells with B cells. Evidence reviewed in this article shows that autoreactive B cells can be driven by the T cells to produce IgG autoantibodies that may be directly involved in joint damage, and B cells are known to be critical in activating CD4+ T cells. As the B cell appears to play an important role in the RA process, it is appropriate to consider how B cell-mediated effects might be reduced or prevented in patients with this disease. As the targeted depletion of B cells with a monoclonal antibody such as rituximab appears to be clinically effective in RA patients, this approach shows great therapeutic potential.

Interferon-inducible p202 in the susceptibility to systemic lupus.

Systemic lupus erythematosus (SLE) is the prototype systemic autoimmune disease, which has potential to involve multiple organ systems. Studies in human SLE patients and murine models of lupus have indicated that genetic predisposition plays a crucial role in the development of this disease. To identify the genetic basis of human lupus and to understand the molecular mechanisms, mouse models of SLE have been studied. Generation of mice congenic for the Nba2 locus on the C57BL/6 genetic background, coupled with gene expression profiling, recently identified the interferon-activatable Ifi202 gene (encodes the protein p202) as a candidate lupus-susceptibility gene. The protein p202 is a member of the 200-protein family. The family includes structurally and functionally related mouse and human interferon-inducible proteins. The protein p202 (52-kDa) is a relatively well-characterized phosphoprotein in the family with demonstrated ability to control cell-signaling pathways regulating cell proliferation, survival, and differentiation. Here, we review what is known about the gene Ifi202 and the protein it encodes. Moreover, we discuss how an understanding of the role of p202 in cell growth regulation, particularly in cells of the immune system, will help elucidate the molecular mechanisms contributing to the development of lupus.

Links between type I interferons and the genetic basis of disease in mouse lupus.

Systemic lupus erythematosus (SLE), like other autoimmune diseases, is a complex genetic trait with contributions from both major histocompatibility complex (MHC) genes and multiple non-MHC genes. Most of the contributing genes have yet to be identified. Studies of mouse models of lupus have provided important insight into the immunopathogenesis of lupus-like IgG autoantibody production and lupus nephritis, and genetic analyses of these mice are helping to unravel the complex and heterogeneous genetic basis of disease. Recent studies in both human SLE and mouse models of lupus have emphasized a potential role of type I interferons (IFN-alpha/beta) in the initiation and perpetuation of disease. There is now increasing interest in genes that affect IFN-alpha/beta expression-activity and IFN-regulated target genes that may be involved in the disease process. One example is interferon-inducible gene 202 (Ifi202), which has been identified as a major candidate susceptibility gene in the New Zealand hybrid model of lupus. Studies suggest that increased expression of this transcription factor leads to lupus through inhibition of lymphocyte apoptosis, although its effects on immune function are extremely complex and have yet to be fully defined. This review will focus on the genetic basis of disease in mouse lupus with a special emphasis on those genetic contributions that may affect IFN-alpha/beta activity and those that may be target genes of IFN-alpha/beta action.

Combined anti-tumor necrosis factor-α therapy and DMARD therapy in rheumatoid arthritis patients reduces inflammatory gene expression in whole blood compared to DMARD therapy alone.

Periodic assessment of gene expression for diagnosis and monitoring in rheumatoid arthritis (RA) may provide a readily available and useful method to detect subclinical disease progression and follow responses to therapy with disease modifying anti-rheumatic agents (DMARDs) or anti-TNF-α therapy. We used quantitative real-time PCR to compare peripheral blood gene expression profiles in active ("unstable") RA patients on DMARDs, stable RA patients on DMARDs, and stable RA patients treated with a combination of a disease-modifying anti-rheumatoid drug (DMARD) and an anti-TNF-α agent (infliximab or etanercept) to healthy human controls. The expression of 48 inflammatory genes were compared between healthy controls (N = 122), unstable DMARD patients (N = 18), stable DMARD patients (N = 26), and stable patients on combination therapy (N = 20). Expression of 13 genes was very low or undetectable in all study groups. Compared to healthy controls, patients with unstable RA on DMARDs exhibited increased expression of 25 genes, stable DMARD patients exhibited increased expression of 14 genes and decreased expression of five genes, and combined therapy patients exhibited increased expression of six genes and decreased expression of 10 genes. These findings demonstrate that active RA is associated with increased expression of circulating inflammatory markers whereas increases in inflammatory gene expression are diminished in patients with stable disease on either DMARD or anti-TNF-α therapy. Furthermore, combination DMARD and anti-TNF-α therapy is associated with greater reductions in circulating inflammatory gene expression compared to DMARD therapy alone. These results suggest that assessment of peripheral blood gene expression may prove useful to monitor disease progression and response to therapy.

Increased expression of Ifi202, an IFN-activatable gene, in B6.Nba2 lupus susceptible mice inhibits p53-mediated apoptosis.

Increased expression of p202 protein (encoded by the Ifi202 gene) in splenocytes derived from B6.Nba2 mice (congenic for the Nba2 interval derived from the New Zealand Black mice) was correlated with defects in apoptosis of splenic B cells and increased susceptibility to develop systemic lupus erythematosus. We have now investigated the molecular mechanisms by which increased expression of p202 in B6.Nba2 cells contributes to defects in apoptosis. In this study, we report that increased expression of p202 in the B6.Nba2 splenocytes, as compared with cells derived from the parental C57BL/6 (B6) mice, was correlated with increased levels of p53 protein and inhibition of p53-mediated transcription of target genes that encode proapoptotic proteins. Conversely, knockdown of p202 expression in B6.Nba2 cells resulted in stimulation of p53-mediated transcription. We found that p202 bound to p53 in the N-terminal region (aa 44-83) comprising the proline-rich region that is important for p53-mediated apoptosis. Consistent with the binding of p202 to p53, increased expression of p202 in B6.Nba2 mouse embryonic fibroblasts inhibited UV-induced apoptosis. Taken together, our observations support the idea that increased expression of p202 in B6.Nba2 mice increases the susceptibility to develop lupus, in part, by inhibiting p53-mediated apoptosis.

Contribution of NZB autoimmunity 2 to Y-linked autoimmune acceleration-induced monocytosis in association with murine systemic lupus.

The accelerated development of systemic lupus erythematosus (SLE) in BXSB male mice is associated with the presence of the Y-linked autoimmune acceleration (Yaa) mutation, which induces an age-dependent monocytosis. Using a cohort of C57BL/6 (B6) x (NZB x B6)F1 backcross male mice bearing the Yaa mutation, we defined the pathogenic role and genetic basis for Yaa-associated monocytosis. We observed a remarkable correlation of monocytosis with autoantibody production and subsequent development of lethal lupus nephritis, indicating that monocytosis is an additional useful indicator for severe SLE. In addition, we identified an NZB-derived locus on chromosome 1 predisposing to the development of monocytosis, which peaked at Fcgr2b encoding FcgammaRIIB and directly overlapped with the previously identified NZB autoimmunity 2 (Nba2) locus. The contribution of Nba2 to monocytosis was confirmed by the analysis of Yaa-bearing B6 mice congenic for the NZB-Nba2 locus. Finally, we observed a very low-level expression of FcgammaRIIB on macrophages bearing the NZB-type Fcgr2b allele, compared with those bearing the B6-type allele, and the development of monocytosis in FcgammaRIIB haploinsufficient B6 mice carrying the Yaa mutation. These data suggest that the Nba2 locus may play a supplementary role in the pathogenesis of SLE by promoting the development of monocytosis and the activation of effector cells bearing stimulatory FcgammaR, in addition to its implication in the dysregulated activation of autoreactive B cells.

Armed CD4+ Th1 effector cells and activated macrophages participate in bile duct injury in murine biliary atresia.

Biliary atresia (BA) is an inflammatory cholangiopathy of infancy. A proposed mechanism regarding the pathogenesis of BA is that of a virus-induced, immune-mediated injury to bile ducts. The rotavirus (RRV)-induced murine model of BA was utilized to determine the hepatic inflammatory response related to ductal obstruction and if the immune response recapitulated human BA. One week after infection, there was a significant increase in liver CD4(+) T cells producing IFN-gamma and in macrophages producing TNF-alpha. The intrahepatic pattern of inflammation evolved rapidly from an initial predominant CD4(+) Th1 cellular response to a subsequent influx of activated macrophages producing TNF-alpha and iNOS. This immune response persisted despite viral clearance and was representative of the hepatic immune profile present in human BA. Utilization of the murine model of BA yielded mechanistic data that can provide much needed insight into the role played by different arms of the immune system related to the pathogenesis of human BA.

Activation pathways implicate anti-HLA-DP and anti-LFA-1 antibodies as lead candidates for intervention in chronic berylliosis.

CD4(+) T cells play a key role in granulomatous inflammation in the lung of patients with chronic beryllium disease. The goal of this study was to characterize activation pathways of beryllium-responsive bronchoalveolar lavage (BAL) CD4(+) T cells from chronic beryllium disease patients to identify possible therapeutic interventional strategies. Our results demonstrate that in the presence of APCs, beryllium induced strong proliferation responses of BAL CD4(+) T cells, production of superoptimal concentrations of secreted proinflammatory cytokines, IFN-gamma, TNF-alpha,and IL-2, and up-regulation of numerous T cell surface markers that would promote T-T Ag presentation. Ab blocking experiments revealed that anti-HLA-DP or anti-LFA-1 Ab strongly reduced proliferation responses and cytokine secretion by BAL CD4(+) T cells. In contrast, anti-HLA-DR or anti-OX40 ligand Ab mainly affected beryllium-induced proliferation responses with little impact on cytokines other than IL-2, thus implying that nonproliferating BAL CD4(+) T cells may still contribute to inflammation. Blockade with CTLA4-Ig had a minimal effect on proliferation and cytokine responses, confirming that activation was independent of B7/CD28 costimulation. These results indicate a prominent role for HLA-DP and LFA-1 in BAL CD4(+) T cell activation and further suggest that specific Abs to these molecules could serve as a possible therapy for chronic beryllium disease.