Spinal radiographic progression over 2 years in ankylosing spondylitis patients treated with secukinumab: a historical cohort comparison.

OBJECTIVE: The aim of this study was to compare radiographic progression in patients with ankylosing spondylitis (AS) treated for up to 2 years with secukinumab (MEASURE 1) with a historical cohort of biologic-naïve patients treated with NSAIDs (ENRADAS). METHODS: Baseline and 2-year lateral cervical and lumbar spine radiographs were independently evaluated using mSASSS by two readers, who were blinded to the chronology and cohort of the radiographs. The primary endpoint was the proportion of patients with no radiographic progression (mSASSS change ≤ 0 from baseline to year 2). The Primary Analysis Set included patients with baseline (≤ day 30) and post-baseline day 31-743 radiographs. Sensitivity analyses were performed to assess the robustness of the comparison between the two cohorts, as follows: Sensitivity Analysis Set 1 included all patients with baseline (≤ day 30) and year 2 (days 640-819) radiographs; Sensitivity Analysis Set 2 included all patients with baseline and post-baseline (> day 30) radiographs. RESULTS: A total of 168 patients (84%) from the MEASURE 1 cohort and 69 (57%) from the ENRADAS cohort qualified for the Primary Analysis Set. Over 2 years, the LS (SE) mean change from baseline in mSASSS for the primary analysis was 0.55 (0.139) for MEASURE 1 vs 0.89 (0.216) for ENRADAS (p = 0.1852). Mean changes from baseline in mSASSS were lower in MEASURE 1 vs ENRADAS for the primary and sensitivity analyses. The proportion of patients with no radiographic progression was consistently higher in the MEASURE 1 vs ENRADAS cohort across all cutoffs for no radiographic progression (change in mSASSS from baseline to year 2 of ≤ 0, ≤ 0.5, ≤ 1, and ≤ 2), but the differences were not statistically significant. CONCLUSION: Secukinumab-treated patients demonstrated a numerical, but statistically non-significant, higher proportion of non-progressors and lower change in mSASSS over 2 years versus a cohort of biologic-naïve patients treated with NSAIDs.

Secukinumab after anti-tumour necrosis factor-α therapy: a phase III study in active rheumatoid arthritis.

OBJECTIVE: To assess the efficacy and safety of secukinumab in patients with rheumatoid arthritis (RA) who failed to respond to tumour necrosis factor- α (TNF-α) inhibitors. METHOD: This phase III double-blind, double-dummy, placebo-controlled study (NCT01770379) randomized (1:1:1) patients to subcutaneous secukinumab 150 mg, secukinumab 75 mg, or placebo at baseline, weeks 1, 2, 3, and 4, and then every 4 weeks. American College of Rheumatology (ACR) 20 response at week 24 was the primary endpoint. Secondary outcomes included the 28-joint Disease Activity Score using C-reactive protein (DAS28-CRP), Health Assessment Questionnaire Disability Index (HAQ-DI), and ACR50 at week 24. Long-term treatment was planned for 5 years. RESULTS: ACR20 response rates at week 24 for the secukinumab 150 mg and 75 mg groups were not statistically superior to placebo. None of the secondary endpoints was met for either secukinumab dose. Although not statistically significant, compared with placebo, numerically greater differences in least squares mean changes from baseline in HAQ-DI score and numerically higher ACR50 response rates were observed at week 24 in both secukinumab treatment groups. No new or unexpected adverse events were observed in this study compared with the large secukinumab safety database across psoriasis, psoriatic arthritis, ankylosing spondylitis, and other RA studies. CONCLUSIONS: Given that other second-line therapies have demonstrated efficacy in RA patients who failed to respond to TNF-α inhibitors, these findings may suggest that interleukin-17A inhibition with secukinumab does not provide additional benefit to these patients. This study further confirms the well-characterized safety profile of secukinumab.

Secukinumab and Sustained Improvement in Signs and Symptoms of Patients With Active Ankylosing Spondylitis Through Two Years: Results From a Phase III Study.

OBJECTIVE: Secukinumab improved the signs and symptoms of ankylosing spondylitis (AS) over 52 weeks in the phase III MEASURE 2 study. Here, we report longer-term (104 weeks) efficacy and safety results. METHODS: Patients with active AS were randomized to subcutaneous secukinumab 150 mg, 75 mg, or placebo at baseline; weeks 1, 2, and 3; and every 4 weeks from week 4. The primary end point was the Assessment of SpondyloArthritis international Society criteria for 20% improvement (ASAS20) response rate at week 16. Other end points included ASAS40, high-sensitivity C-reactive protein, ASAS5/6, Bath Ankylosing Spondylitis Disease Activity Index, Short Form 36 health survey physical component summary, ASAS partial remission, EuroQol 5-domain measure, and Functional Assessment of Chronic Illness Therapy fatigue subscale. End points were assessed through week 104, with multiple imputation for binary variables and a mixed-effects model repeated measures for continuous variables. RESULTS: Of 219 randomized patients, 60 of 72 (83.3%) and 57 of 73 (78.1%) patients completed 104 weeks of treatment with secukinumab 150 mg and 75 mg, respectively; ASAS20/ASAS40 response rates at week 104 were 71.5% and 47.5% with both secukinumab doses, respectively. Clinical improvements with secukinumab were sustained through week 104 across all secondary end points. Across the entire treatment period (mean secukinumab exposure 735.6 days), exposure-adjusted incidence rates for serious infections and infestations, Crohn's disease, malignant or unspecified tumors, and major adverse cardiac events with secukinumab were 1.2, 0.7, 0.5, and 0.7 per 100 patient-years, respectively. No cases of tuberculosis reactivation, opportunistic infections, or suicidal ideation were reported. CONCLUSION: Secukinumab provided sustained improvement through 2 years in the signs and symptoms of AS, with a safety profile consistent with previous reports.

Efficacy and safety of secukinumab in the treatment of moderate-to-severe plaque psoriasis: a randomized, double-blind, placebo-controlled phase II dose-ranging study.

BACKGROUND: Conventional systemic therapies for plaque psoriasis have not fully met the needs of patients, and although current biologic treatments are generally well tolerated, concerns exist with respect to long-term safety. Interleukin (IL)-17A is believed to be an important effector cytokine in the pathogenesis of psoriasis and is produced by Th17 cells, a class of helper T cells that act outside the established Th1/Th2 paradigm for regulation of innate and adaptive immunity. OBJECTIVES: To assess the efficacy and safety of different doses of secukinumab, a fully human anti-IL-17A IgG1κ monoclonal antibody, in patients with moderate-to-severe plaque psoriasis. METHODS: Patients (n = 125) were randomized 1 : 1 : 1 : 1 : 1 to receive subcutaneous doses of placebo (n = 22) or secukinumab [1 × 25 mg (n = 29), 3 × 25 mg (n = 26), 3 × 75 mg (n = 21) or 3 × 150 mg (n = 27)] at weeks 0, 4 and 8. After the 12-week treatment period, patients entered a follow-up period of 24 weeks. The primary efficacy outcome was at least 75% improvement from baseline in the Psoriasis Area and Severity Index score (PASI 75); secondary outcomes included the Investigator's Global Assessment (IGA) and PASI 90 and 50 response rates. RESULTS: After 12 weeks of treatment, secukinumab 3 × 150 mg and 3 × 75 mg resulted in significantly higher PASI 75 response rates vs. placebo (82% and 57% vs. 9%; P < 0·001 and P = 0·002, respectively). Higher PASI 75 response rates compared with placebo were maintained throughout the follow-up period with these dosages [week 36, 26% (n = 7) and 19% (n = 4) vs. 4% (n = 1), respectively], with a gradual decline of PASI 75 response over time after the dosing period. IGA response rates were significantly higher in the 3 × 150 mg group vs. placebo at week 12 (48% vs. 9%; P = 0·005) and were consistently higher for the 3 × 150 mg and 3 × 75 mg groups vs. placebo at all time points from week 4 onward. The PASI 90 response rate was significantly higher in the 3 × 150 mg group vs. placebo (52% vs. 5%) at week 12 and remained higher during the follow-up period. Secukinumab was well tolerated. Two cases of neutropenia (≤ grade 2) were reported in the 3 × 150 mg cohort. CONCLUSIONS: Treatment with subcutaneous secukinumab 3 × 75 mg and 3 × 150 mg met the primary outcome of PASI 75 response achievement after 12 weeks, demonstrating efficacy in moderate-to-severe psoriasis.

Overexpression of interleukin-12 and T helper 1 predominance in lupus nephritis.

Imbalance of cytokine homeostasis is a prominent feature of both experimental and human systemic lupus erythematosus (SLE). Because interleukin (IL)-12 promotes interferon (IFN)-gamma production leading to polarization of peripheral cells toward a T helper (Th) 1 phenotype, we investigated its role in lupus nephritis (LN). Soluble Th1 and Th2 cytokines were measured by enzyme-linked immunosorbent assay (ELISA) in sera and urines of SLE patients and controls. Th1/Th2 peripheral lymphocyte polarization was determined by flow cytometry. Glomerular accumulation of IL-12 was evaluated by immunohistochemistry, whereas urinary IL-12 was evaluated by ELISA. Higher serum IL-12 levels in SLE were associated with LN, whereas IL-4 was unrelated to the renal damage. Peripheral cells from LN patients showed a Th1 phenotype with a high IFN-gamma expression that paralleled the severity of renal damage. IL-12 was present within glomerular mononuclear cells in classes IV and V LN, and its accumulation was correlated strongly with urinary levels. IL-12 overexpression in SLE may contribute to the development of LN. Both serum and urinary IL-12 elevation reflect its glomerular production and parallel Th1 polarization of peripheral T cells and high IFN-gamma production. In SLE patients, IL-12 measurement may thus be predictive of the development of LN.

High sensitivity C-reactive protein in systemic lupus erythematosus: relation to disease activity, clinical presentation and implications for cardiovascular risk.

Measurement of high sensitivity C-reactive protein (hs-CRP), has been used in the assessment of disease activity in numerous rheumatic conditions including systemic lupus erythematosus (SLE). However, the utility of hs-CRP measurement in patients with lupus is uncertain. This study examined if hs-CRP can be used to assess disease activity, severity and cardiovascular risk in SLE. Serum samples from 601 visits of 213 SLE patients and 134 controls were analysed for hs-CRP by nephelometry. Detailed demographic data were obtained from all subjects and medication history and key laboratory parameters were collected. Disease activity was assessed using the SLEDAI. High sensitivity CRP was not associated with disease activity (SLEDAI), number of ACR SLE criteria or presence of any particular organ involvement. hs-CRP levels were significantly correlated with standard cardiovascular risk factors including body weight (P = 0.0002), hypertension (P = 0.001), and apolipoprotein A-I (P < 0.0001). Interestingly an inverse correlation was seen between hs-CRP levels and antimalarial use (P = 0.0018). Our results suggest that measurement of hs-CRP, though not valuable as marker of disease activity in SLE may be of some use in the assessment of cardiovascular risk. We speculate that antimalarials may help to reduce cardiovascular risk in patients with SLE.

Up-regulation of IL-18 and predominance of a Th1 immune response is a hallmark of lupus nephritis.

There is evidence that nephritis is dominated by a Th1 immune response in systemic lupus erythematosus. Since IL-18 promotes polarization of the immune response toward Th1, we investigated the role of this cytokine in lupus nephritis (LN). A total of 133 lupus patients and 44 healthy subjects were enrolled. Demographic and clinical characteristics with renal biopsy data were recorded. IL-18 along with IFN-gamma and IL-4, two prototypical of Th1 and Th2 cytokines, were measured in serum by ELISA. Peripheral blood lymphocytes were analysed by flow cytometry for IFN-gamma and IL-4. IL-18 expression was determined by immunohistochemistry in 13 renal biopsy specimens from patients with LN and 2 controls. Serum IL-18 was higher in lupus patients than in controls. Levels of IL-18 correlated with urinary microalbumin and were increased in patients with LN when compared to those without LN. IL-18 expression was also increased within the glomeruli of nephritic patients and was primarily detected within the mesangial matrix and in infiltrating mononuclear cells. Measurement of IFN-gamma and IL-4 in either sera or peripheral blood lymphocytes showed high IFN-gamma along with low IL-4 expression in LN patients compared to patients without nephritis. A positive correlation between serum IL-18 and IFN-gamma levels was found. IL-18 may play a prominent role in the pathogenesis of LN by promoting a cytokine imbalance towards a Th1 immune response. Measurement of IL-18 may be helpful for the early identification of lupus patients with LN and may help gauge the response to treatment in patients with active LN undergoing treatment.

Interferon-gamma is required for lupus nephritis in mice treated with the hydrocarbon oil pristane.

BACKGROUND: Although the precise mechanisms leading to lupus nephritis remain obscure, both TH1 and TH2 cytokines have been implicated. The present study examined the roles of interleukin (IL)-4 and interferon-gamma (IFN-gamma) in a novel inducible form of lupus that develops in non-autoimmune mice treated with the hydrocarbon oil pristane. METHODS: BALB/c IL-4 or IFN-gamma deficient mice (IL-4 -/-, IFNgamma -/-) and wild type controls (+/+) received either pristane or phosphate-buffered saline (PBS) IP. Serial sera were analyzed for anti-DNA/chromatin, anti-RNP/Sm, and total immunoglobulin levels. Proteinuria was measured and kidneys were examined by direct immunofluorescence and light microscopy. RESULTS: Renal disease did not develop in pristane-treated IFN-gamma -/- mice, as assessed by the absence of capillary immune deposits, glomerular pathology and proteinuria whereas IL-4 -/- mice developed renal disease similar to +/+ mice. Production of IgG anti-single stranded DNA and anti-chromatin antibodies was abrogated in IFN-gamma -/- mice. In contrast, these autoantibodies were produced at similar or higher frequencies and levels by IL-4 -/- versus wild-type mice. The frequency of anti-nRNP/Sm was markedly reduced in IFN-gamma -/- mice. IL-4 deficiency had little effect on the production of anti-DNA/chromatin and anti-nRNP/Sm. CONCLUSIONS: IFN-gamma is essential for the induction of nephritis and anti-DNA/chromatin following pristane exposure in BALB/c mice, suggesting that genetic or environmental factors influencing TH1-TH2 balance could be an important determinant of renal disease in lupus.

Titration emulation: a computer-assisted technique that simplifies the quantification of anti-dsDNA antibodies using the Crithidia luciliae assay.

Titers of anti-double-stranded (ds) DNA antibodies in sera from patients with systemic lupus erythematosus (SLE) using the Crithidia luciliae assay method were compared by conventional titration vs the titration emulation method (ImageTiter) to evaluate whether the latter assay can replace manual titration. Titers by the two methods were identical or within one dilution in 98% (41/42) of samples. A single sample showed a two-dilution difference. Titration emulation showed a tendency to under-estimate the titer of high titer anti-dsDNA samples, although the difference was small. Titration emulation is a suitable alternative to the conventional titration method, offering an accurate and cost-effective approach to quantification of anti-dsDNA antibodies.

Increased prevalence of autoantibodies to ku antigen in African American versus white patients with systemic lupus erythematosus.

OBJECTIVE: To investigate whether the widely varying estimates of the prevalence of anti-Ku autoantibodies are explained by racial/ethnic differences. METHODS: Consecutive African American or white patients who met the 1982 criteria for systemic lupus erythematosus (SLE) and who were evaluated over 10 years in North Carolina, Florida, and New York were tested by immunoprecipitation of K562 cell extract for anti-Ku as well as anti-nuclear RNP (nRNP)/Sm, anti-Ro/SSA, and anti-La/SSB autoantibodies. RESULTS: Anti-Ku autoantibodies were detected in sera from 18 of 155 African American patients with SLE (12%) versus 0 of 126 white patients (P < 0.0001, by Fisher's exact test). Anti-nRNP (63% versus 16%; P < 0.0001) and anti-Sm (23% versus 7%; P < 0.0004) autoantibodies were also more common in the African American subset. The 2 groups had comparable frequencies of anti-Ro/SSA and anti-La/SSB autoantibodies. CONCLUSION: Anti-Ku antibodies are common in African American patients with SLE but rare in whites, probably explaining the different estimates of their prevalence. In African Americans, the frequency is comparable with that of anti-La/SSB. Along with anti-Ku, anti-nRNP and anti-Sm autoantibodies are also overrepresented in African Americans, suggesting that a group of specificities is characteristically associated with SLE in African Americans.

Widespread susceptibility among inbred mouse strains to the induction of lupus autoantibodies by pristane.

Unlike other agents associated with drug-induced lupus, the isoprenoid alkane pristane induces autoantibodies pathognomonic of lupus, including anti-Sm, anti-dsDNA, and anti-ribosomal P in BALB/c and SJL/J mice. The susceptibility of other strains of mice to pristane-induced lupus is unknown and is the focus of the present study. Anti-nRNP/Sm, anti-Su, and anti-ribosomal P autoantibodies were produced by most strains of mice surveyed within several months of pristane treatment, although there was marked interstrain variability in their frequencies, levels, and times of onset. In sharp contrast, the production of autoantibodies against the double-stranded RNA binding proteins NF45/NF90/p110 was restricted to B6 and B10.S mice. We conclude that pristane selectively induces lupus-specific autoantibodies in virtually any strain of mouse regardless of its genetic background. However, H-2-linked as well as non-H2 genes influenced the expression of individual autoantibody markers. The widespread susceptibility of pristane-treated mice to lupus autoantibody production and the relatively small effect of MHC are unique features of this chemically induced lupus syndrome, with potential implications for understanding the pathogenesis of autoantibodies in idiopathic human systemic lupus erythematosus.

Fas and Fas ligand mutations inhibit autoantibody production in pristane-induced lupus.

Mutations of Fas (lpr) or Fas ligand (gld) cause a limited lupus-like syndrome in B6 mice by interfering with the deletion of autoreactive B and/or T cells. A more generalized lupus syndrome reminiscent of that of MRL mice can be induced in nonautoimmune strains by pristane, which causes a nonspecific inflammatory response in the peritoneal cavity. We hypothesized that, as in MRL mice, the lpr and gld mutations might accelerate lupus in pristane-treated mice. Pristane-treated B6 mice developed anti-nRNP/Sm, Su, and ribosomal P Abs, but little anti-ssDNA or chromatin. In contrast, B6/lpr and B6/gld mice spontaneously developed anti-ssDNA/chromatin Abs, but not anti-nRNP/Sm/Su/ribosomal P. Unexpectedly, B6/lpr and B6/gld mice were highly resistant to the induction by pristane of IgM anti-ssDNA (2 wk) and IgG anti-nRNP/Sm/Su/ribosomal P autoantibodies (6 mo), suggesting that intact Fas signaling is necessary. Interestingly, pristane did not enhance IgG chromatin Ab production in B6/lpr or B6/gld mice, suggesting that it did not influence the production of autoantibodies that develop spontaneously in the setting of Fas deficiency. Pristane treatment also decreased lymphoproliferation in B6/lpr mice. Increased production of IL-12 was associated consistently with the production of anti-nRNP/Sm/Su/ribosomal P as well as anti-DNA/chromatin. In contrast, production of anti-DNA/chromatin Abs was associated with IL-6 overproduction in pristane-treated mice, but not in lpr mice. The data strongly support the idea that different subsets of autoantibodies are regulated differentially by cytokine stimulation and/or Fas signaling.

Autoantibodies define a family of proteins with conserved double-stranded RNA-binding domains as well as DNA binding activity.

Cellular responses to viral infection are signaled by double-stranded (ds) RNA, which is not found in substantial amounts in uninfected cells. Although cellular dsRNA-binding proteins have been described, their characterization is incomplete. We show that dsRNA-binding proteins are prominent autoantigens. Sera from B6 and B10.S mice with pristane-induced lupus and human autoimmune sera immunoprecipitated a novel set of 130-, 110-, 90-, 80-, and 45-kDa proteins. The proteins were all major cellular poly(IC)-binding factors. N-terminal amino acid sequences of p110 and p90 were identical and matched nuclear factor (NF) 90 and M phase phosphoprotein 4. p45 and p90 were identified as the NF45.NF90 complex, which binds the interleukin-2 promoter as well as certain highly structured viral RNAs. NF90.NF45 and M phase phosphoprotein 4 belong to a large group of proteins with conserved dsRNA-binding motifs. Besides binding dsRNA, NF90.NF45, p110, and p130 had single-stranded and dsDNA binding activity. Some sera contained autoantibodies whose binding was inhibited by poly(IC) but not single-stranded DNA or vice versa, suggesting that the DNA- and RNA-binding sites are different. These autoantibodies will be useful probes of the function of dsRNA-binding proteins. Their interaction with dsRNA, an immunological adjuvant, also could promote autoimmunity.

Immunopathogenesis of environmentally induced lupus in mice.

Systemic lupus erythematosus (SLE) is a systemic autoimmune syndrome defined by clinical and serologic features, including arthritis, glomerulonephritis, and certain autoantibodies such as anti-nuclear ribonucleoprotein (nRNP)/Smith antigen (Sm), DNA, and ribosomal P. Although lupus is considered primarily a genetic disorder, we recently demonstrated the induction of a syndrome strikingly similar to spontaneous lupus in many nonautoimmune strains of mice exposed to the isoprenoid alkane pristane (2,6,10,14-tetramethylpentadecane), a component of mineral oil. Intraperitoneal injection of pristane leads to the formation of lipogranulomas consisting of phagocytic cells that have engulfed the oil and collections of lymphocytes. Subsequently, pristane-treated BALB/c and SJL mice develop autoantibodies characteristic of SLE, including anti-nRNP/Sm, antiribosomal P, anti-Su, antichromatin, anti-single-stranded DNA, and anti-double-stranded DNA. This is accompanied by a severe glomerulonephritis with immune complex deposition, mesangial or mesangiocapillary proliferation, and proteinuria. All inbred mice examined appear to be susceptible to this novel form of chemically induced lupus. Pristane-induced lupus is the only inducible model of autoimmunity associated with the clinical syndrome as well as with the characteristic serologic abnormalities of SLE. Defining the immunopathogenesis of pristane-induced lupus in mice may provide insight into the causes of spontaneous (idiopathic) lupus and also may lead to information concerning possible risks associated with the ingestion or inhalation of mineral oil and exposure to hydrocarbons in the environment.

Disparate T cell requirements of two subsets of lupus-specific autoantibodies in pristane-treated mice.

Intraperitoneal injection of pristane induces a lupus-like disease in BALB/c and other non-autoimmune mice characterized by autoantibody production and the development of immune complex disease closely resembling lupus nephritis. Two subsets of autoantibodies are induced by pristane: IgG anti-DNA DNA and -chromatin autoantibodies are strongly IL-6-dependent, whereas IgG anti-nRNP/Sm and -Su antibodies are not. The present studies were carried out to examine the role of T cells in establishing this dichotomy between the production of anti-nRNP/Sm/Su versus anti-DNA/chromatin autoantibodies. Autoantibody production and renal disease were evaluated in athymic (nude) mice treated with pristane. BALB/c nu/nu mice spontaneously developed IgM and IgG anti-single-stranded (ss)DNA and -chromatin, but not anti-nRNP/Sm or -Su, autoantibodies. Pristane treatment increased the levels of IgG anti-chromatin antibodies in nu/nu mice, but did not induce production of anti-nRNP/Sm or -Su antibodies. In contrast, BALB/c nu/+ and +/+ control mice did not spontaneously produce autoantibodies, whereas anti-nRNP/Sm and -Su autoantibodies were induced by pristane in approx. 50% of nu/+ and +/+ mice and anti-DNA/chromatin antibodies at lower frequencies. Nude mice spontaneously developed mild renal lesions that were marginally affected by pristane, but were generally milder than the lesions developing in pristane-treated nu/+ and +/+ mice. The data provide further evidence that two distinct pathways with different cytokine and T cell requirements are involved in autoantibody formation in pristane-induced lupus. This dichotomy may be relevant to understanding differences in the regulation of anti-DNA versus anti-nRNP/Sm autoantibodies in systemic lupus erythematosus, as well as the association of anti-DNA, but not anti-nRNP/Sm, with lupus nephritis.

Interleukin 6 dependence of anti-DNA antibody production: evidence for two pathways of autoantibody formation in pristane-induced lupus.

Pristane induces a lupus-like syndrome in nonautoimmune mice characterized by the development of glomerulonephritis and lupus-associated autoantibodies. This is accompanied by overproduction of interleukin (IL)-6, a cytokine linked with autoimmune phenomena. The goal of this study was to evaluate the role of IL-6 in autoantibody production in pristane-induced lupus. BALB/cAn IL-6-deficient (-/-) and -intact (+/+) mice were treated with pristane or phosphate-buffered saline, and autoantibody production was evaluated. Pristane induced high levels of immunoglobulin (Ig)G anti-single-stranded DNA, -double-stranded (ds)DNA, and -chromatin antibodies in IL-6(+/+), but not IL-6(-/-) mice by enzyme-linked immunosorbent assay. High titer IgG anti-dsDNA antibodies also were detected in sera from +/+, but not -/-, mice by Crithidia luciliae kinetoplast staining. The onset of IgG anti-dsDNA antibody production in +/+ mice occurred >5 mo after pristane treatment, well after the onset of nephritis, suggesting that these antibodies are not directly responsible for inducing renal disease. In contrast to anti-DNA, the frequencies of anti-nRNP/Sm and anti-Su antibodies were similar in pristane-treated IL-6(-/-) and IL-6(+/+) mice. However, levels were higher in the +/+ group. These results suggest that IgG anti-DNA and chromatin antibodies in pristane-treated mice are strictly IL-6 dependent, whereas induction of anti-nRNP/Sm and Su autoantibodies is IL-6 independent. The IL-6 dependence of anti-DNA, but not anti-nRNP/Sm, may have implications for understanding the patterns of autoantibody production in lupus. Anti-DNA antibodies are produced transiently, mainly during periods of disease activity, whereas anti-nRNP/Sm antibody levels are relatively insensitive to disease activity. This may reflect the differential IL-6 dependence of the two responses.

Influence of microbial stimulation on hypergammaglobulinemia and autoantibody production in pristane-induced lupus.

Pristane induces a lupus-like syndrome characterized by autoantibody production and glomerulonephritis in nonautoimmune strains of mice. Although it has been suggested that this syndrome results from nonspecific immune activation, there is little evidence so far that B cells are activated nonspecifically by pristane or that this promotes autoimmunity. In this study, we examined whether polyclonal hypergammaglobulinemia occurs in pristane-induced lupus, and its relationship to the production of anti-DNA, nRNP/Sm, and Su autoantibodies. In conventionally housed mice, there was a marked increase in total IgM and IgG3 2 weeks after i.p. pristane injection, followed by increased IgG1, IgG2a, and IgG2b levels. IgM levels were higher in pristane-treated specific pathogen-free (SPF) mice than in conventionally housed mice, whereas IgG and IgA levels were reduced. Pristane induced anti-nRNP/Sm and Su autoantibodies in SPF mice, but their onset was delayed and levels were lower than those in conventionally housed mice. There was no consistent relationship between total IgG1, 2a, and 2b hypergammaglobulinemia and production of anti-nRNP/Sm and Su autoantibodies. Moreover, the total Ig levels were similar in the anti-nRNP/Sm-positive and -negative groups. In contrast, production of IgM anti-ssDNA antibodies paralleled IgM hypergammaglobulinemia in some, but not all, mice. These studies indicate that pristane-induced lupus is associated with marked hypergammaglobulinemia, the magnitude of which is influenced by the microbial environment. However, anti-nRNP/Sm and Su autoantibody production is at least partly independent of polyclonal B cell activation. The data strongly suggest that pristane-induced lupus is not exclusively the consequence of nonspecific immune stimulation. They also point to the importance of microbial stimulation in the development of hypergammaglobulinemia in this inducible lupus model.