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Some autoimmune diseases, including rheumatoid arthritis (RA), are preceded by a critical subclinical phase of disease activity. Proactive clinical management is hampered by a lack of biological understanding of this subclinical at-risk state and the changes underlying disease development. In a cross-sectional and longitudinal multi-omics study of peripheral immunity in the autoantibody-positive at-risk for RA period, we identified systemic inflammation, proinflammatory-skewed B cells, expanded Tfh17-like cells, epigenetic bias in naive T cells, TNF+IL1B+ monocytes resembling a synovial macrophage population, and CD4 T cell transcriptional features resembling those suppressed by abatacept (CTLA4-Ig) in RA patients. Our findings characterize pathogenesis prior to clinical diagnosis and suggest the at-risk state exhibits substantial immune alterations that could potentially be targeted for early intervention to delay or prevent autoimmunity. We provide a suite of tools at https://apps.allenimmunology.org/aifi/insights/ra-progression/ to facilitate exploration and enhance accessibility of this extensive dataset.

Background: Cytomegalovirus (CMV) chronic retinal necrosis (CRN) is a rare viral retinal infection that occurs in mildly immunocompromised people. It shares some features with both acute retinal necrosis and CMV retinitis. It is typically treated with combination intravitreal and systemic ganciclovir. We discuss the management of a case of CMV CRN with ganciclovir resistance., Case Presentation: An 80-year-old female presented with one month of blurry vision in the left eye. She was being treated with abatacept, methotrexate, and prednisone for rheumatoid arthritis. Examination revealed anterior chamber and vitreous cell along with peripheral retinal whitening. Fluorescein angiogram showed diffuse retinal non-perfusion. Aqueous fluid PCR testing returned positive for CMV. The retinitis was initially controlled with oral and intravitreal ganciclovir, but then recurred and progressed despite these therapies. Ganciclovir resistance was suspected and the patient was switched to intravitreal foscarnet injections, along with oral letermovir and leflunomide, which lead to resolution of the retinitis. The patient has now continued with letermovir and leflunomide for approximately 2.5 years without reactivation of the retinitis or need for further intravitreal anti-viral injections and with adequate control of her rheumatoid arthritis., Conclusion: The incidence of CMV CRN may increase in the future as the use of non-cytotoxic immunosuppressive therapies that result in relatively mild immunosuppression also increases. Treatment with ganciclovir is effective but frequently leads to resistance, as in our case. In this situation, combination therapy with letermovir and leflunomide, particularly in the setting of rheumatoid arthritis where leflunomide can also have an anti-inflammatory effect, can be considered., (© 2024. The Author(s).)

Molecular markers of autoimmunity, such as antibodies to citrullinated protein antigens (ACPA), are detectable prior to inflammatory arthritis (IA) in rheumatoid arthritis (RA) and may define a state that is 'at-risk' for future RA. Here we present a cross-sectional comparative analysis among three groups that include ACPA positive individuals without IA (At-Risk), ACPA negative individuals and individuals with early, ACPA positive clinical RA (Early RA). Differential methylation analysis among the groups identifies non-specific dysregulation in peripheral B, memory and naïve T cells in At-Risk participants, with more specific immunological pathway abnormalities in Early RA. Tetramer studies show increased abundance of T cells recognizing citrullinated (cit) epitopes in At-Risk participants, including expansion of T cells reactive to citrullinated cartilage intermediate layer protein I (cit-CILP); these T cells have Th1, Th17, and T stem cell memory-like phenotypes. Antibody-antigen array analyses show that antibodies targeting cit-clusterin, cit-fibrinogen and cit-histone H4 are elevated in At-Risk and Early RA participants, with the highest levels of antibodies detected in those with Early RA. These findings indicate that an ACPA positive at-risk state is associated with multifaceted immune dysregulation that may represent a potential opportunity for targeted intervention., (© 2023. The Author(s).)

Objective: In rheumatoid arthritis (RA), anti-citrullinated protein antibodies (ACPA) can be elevated prior to inflammatory arthritis (IA). The potential to intervene in people with ACPA positivity underpins the development of prevention trials in RA. The Research Participation Influences Study examined factors influencing the decisions of individuals who are ACPA(+) to participate in a prevention trial using qualitative and quantitative methods., Methods: Individuals with ACPA positivity without IA were provided information regarding their risk for future RA, were provided a description of a clinical prevention trial using hydroxychloroquine, and were asked if they would participate in the trial. After agreeing to or declining participation, they were surveyed on what influenced their decision using Likert scales and open-response questions., Results: Thirty-nine individuals who agreed to trial participation (enrollees) and 31 individuals who declined (nonenrollees) completed surveys. Enrollees expressed greater perceived risk for RA and greater perception of benefit to themselves or others than nonenrollees. Nonenrollees expressed greater concern about medication effects and less personal or family experience with RA than enrollees. There was a higher proportion of first-degree relatives (FDRs) of people with RA in enrollees versus nonenrollees (54% vs. 23%, P = 0.01)., Conclusion: Enrollees were more likely than nonenrollees to be FDRs, exhibit stronger concern for personal risk for RA, and have less concern about adverse effects. Further exploration is needed to determine why these differences were present, including exploration of symptoms and the role of family history. Understanding these issues will better inform researchers and individuals who are candidates for prevention., (© 2022 The Authors. ACR Open Rheumatology published by Wiley Periodicals LLC on behalf of American College of Rheumatology.)

Background/purpose: In rheumatoid arthritis (RA) autoantibodies including antibodies to citrullinated protein antigens (ACPA) and rheumatoid factor (RF) can be predictive of incident clinical RA. However, there is limited understanding of how antibody changes over time impact prediction of the likelihood and timing of future clinical RA., Materials and Methods: We evaluated relationships between ACPA, the shared epitope (SE), RF isotypes and incident RA in a prospective cohort of 90 ACPA(+) individuals without baseline arthritis identified through health-fair testing (i.e. Healthfair). We also evaluated ACPA and RF isotypes and time-to-diagnosis of RA in a retrospective cohort of 215 individuals with RA from the Department of Defense Serum Repository (DoDSR)., Results: Twenty-six of 90 (29%) of ACPA(+) Healthfair participants developed incident RA. Baseline or incident dual RF-IgA and RF-IgM positivity was associated with increased risk for incident RA (HR 3.09; 95% CI 1.15 to 8.29) although RFs were negative in ~50% of individuals with incident RA. SE was associated with increased risk of RA (HR 2.87, 95% CI 1.22-6.76). In the DoDSR cohort, triple positivity for ACPA, RF-IgA and RF-IgM was present a median of 1-2 years prior to RA diagnosis, with some sex-specific differences., Conclusion: These findings can be used to counsel individuals at-risk for future RA and to design clinical trials for RA prevention. The findings also suggest that RF could be a surrogate outcome as a success of an immunologic intervention in RA prevention. Additional studies are needed to understand the biologic of different patterns of autoantibody elevations in RA evolution., Competing Interests: KD has received free materials for autoantibody testing from Inova Diagnostics, Inc., and he has also served as an advisor for Inova Diagnostics, Inc. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Bergstedt, Tarter, Peterson, Feser, Parish, Striebich, Demoruelle, Moss, Bemis, Norris, Holers, Edison, Thiele, Mikuls and Deane.)

Rheumatoid arthritis (RA) is a systemic and incurable autoimmune disease characterized by chronic inflammation in synovial lining of joints. To identify the signaling pathways involved in RA, its disease activity, and treatment response, we adapted a systems immunology approach to simultaneously quantify 42 signaling nodes in 21 immune cell subsets (e.g., IFNα→p-STAT5 in B cells) in peripheral blood mononuclear cells (PBMC) from 194 patients with longstanding RA (including 98 patients before and after treatment), and 41 healthy controls (HC). We found multiple differences between patients with RA compared to HC, predominantly in cytokine-induced Jak/STAT signaling in many immune cell subsets, suggesting pathways that may be associated with susceptibility to RA. We also found that high RA disease activity, compared to low disease activity, was associated with decreased (e.g., IFNα→p-STAT5, IL-10→p-STAT1) or increased (e.g., IL-6→STAT3) response to stimuli in multiple cell subsets. Finally, we compared signaling in patients with established, refractory RA before and six months after initiation of methotrexate (MTX) or TNF inhibitors (TNFi). We noted significant changes from pre-treatment to post-treatment in IFNα→p-STAT5 signaling and IL-10→p-STAT1 signaling in multiple cell subsets; these changes brought the aberrant RA signaling profiles toward those of HC. This large, comprehensive functional signaling pathway study provides novel insights into the pathogenesis of RA and shows the potential of quantification of cytokine-induced signaling as a biomarker of disease activity or treatment response., Competing Interests: The authors have read the journal’s policies and declare the following competing interest: Nodality, Inc., a now inactive company, provided in-kind support for this work and investigators at Nodality played important roles in the study design, hands-on analysis of samples, and preparation of the manuscript. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Objective: The aim of this study was to determine the association of perceived stress with incident inflammatory arthritis (IA) defined as having at least 1 joint consistent with rheumatoid arthritis (RA)-like synovitis based on examination., Methods: We conducted a prospective cohort study in the Studies of the Etiologies of Rheumatoid Arthritis cohort. Participants without IA were recruited if they were a first-degree relative of an RA proband or screened positive for anti-citrullinated protein antibody. Perceived stress was measured using the Perceived Stress Scale-14 (PSS-14), in which scores can range from 0 to 56, and a higher score indicates greater perceived stress. The total PSS-14 score, as well as 2 subscores indicative of perceived distress and self-efficacy, were averaged across all study visits until development of IA or the last follow-up. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) of IA associated with average PSS-14 scores were obtained using Cox proportional hazards models., Results: The mean total PSS-14 score was 20.4. We found that a 1-point increase in the perceived distress score was significantly associated with a 10-percent increase in the risk of IA (adjusted HR 1.10 [95% CI 1.02-1.19]). Total PSS-14 and self-efficacy were not associated with IA risk (adjusted HR 1.05 [95% CI 0.99-1.10] and 1.04 [95% CI 0.91-1.18], respectively)., Conclusion: An association between perceived distress and incident IA was observed in this at-risk cohort. Replication of this finding in other preclinical and at-risk RA populations is needed., (© 2020, American College of Rheumatology.)

Objectives: 3-hydroxy-3-methylglutaryl coenzyme-A (HMG Co-A) reductase inhibitors (statins) are standard treatment for hyperlipidaemia. In addition to lipid-lowering abilities, statins exhibit multiple anti-inflammatory effects. The objectives of this study were to determine whether treatment of patients with RA with lovastatin decreased CRP or reduced disease activity., Methods: We conducted a randomized double-blind placebo-controlled 12 week trial of lovastatin vs placebo in 64 RA patients with mild clinical disease activity but an elevated CRP. The primary efficacy end point was the reduction in mean log CRP. Secondary end points included disease activity, RF and anti-CCP antibody titres. Mechanistic end points included levels of serum cytokines. Safety was assessed; hepatic and muscle toxicities were of particular interest., Results: Baseline features were similar between groups. No significant difference in mean log CRP reduction between the two groups was observed, and disease activity did not change from baseline in either treatment group. Mechanistic analyses did not reveal significant changes in any biomarkers. A post hoc analysis of subjects not using biologic therapy demonstrated a significantly greater proportion achieving ⩾20% reduction in CRP from baseline in the lovastatin group compared with placebo (P-value = 0.007). No difference was observed in subjects receiving biologics. Lovastatin was well tolerated with no serious safety concerns., Conclusion: This study showed no anti-inflammatory or clinical effects on RA disease activity after 12 weeks of treatment with lovastatin. Lovastatin had a modest effect on CRP in subjects not using biologics, suggesting statins may be anti-inflammatory in selected patients., Trial Registration: ClinicalTrials.gov, http://clinicaltrials.gov, NCT00302952., (© The Author(s) 2019. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Objective: To evaluate the effectiveness of pre-appointment consult screening to identify patients with autoimmune and inflammatory rheumatic disease (AIRD) and to evaluate the revenue implications of routine outpatient care of patients with AIRD compared to that of non-AIRD patients., Methods: Using data in the electronic medical records, we retrospectively analyzed all new outpatients who were referred for rheumatology consults during a 9-month period for a final diagnosis and revenue generation for routine outpatient care over 1 year following the consult review or initial evaluation., Results: A total of 961 patients were referred to the outpatient rheumatology clinic and underwent pre-appointment triage. Overall, 673 patients were approved for evaluation of AIRD, and 288 patients were denied rheumatology consultation. Patients were seen an average of 13 days after the consult review. Among patients who were approved for consult, 597 came for evaluation, with 357 diagnosed as having an AIRD and 240 with a non-AIRD. Among patients who were denied a consult, 128 had 1-year follow-up data, with 6 patients eventually diagnosed as having an AIRD (consult triage sensitivity 98%, positive predictive value 60%). The consult triage system allowed more AIRD patients to be seen over a 1-year period. Revenue data for outpatient care was available for 318 of 357 patients with an AIRD and 192 of 240 non-AIRD patients and showed that care for patients with an AIRD generates 44 times more revenue compared to care for non-AIRD patients ($5,877 per AIRD patient versus $134 per non-AIRD patient; P < 0.001)., Conclusion: Pre-appointment consult screening is an effective method to identify patients with an AIRD. This approach enables timely access to care for patients with the highest need for evaluation and results in significantly more revenue generation., (© 2018, American College of Rheumatology.)

Objectives: Higher circulating omega-3 fatty acids (n-3 FAs) are associated with a lower prevalence of anti-CCP antibodies and RF in subjects without RA. We examined whether, in anti-CCP+ subjects, n-3 FAs also play a role in development of inflammatory arthritis (IA)., Methods: At Colorado-based health fairs from 2008 to 2014, participants without a previous diagnosis of RA who were anti-CCP3+ (n = 47) were recruited into a follow-up study; symptom assessments and joint examinations were conducted every 6 months for the determination of IA. We measured n-3 FAs as a percentage of total lipids in red blood cell membranes (n-3 FA%) at each visit., Results: We detected IA in 10 anti-CCP3+ subjects (21%) at the baseline visit. Increased total n-3 FA% in red blood cell membranes [odds ratio (OR) = 0.09, 95% CI: 0.01, 0.76], specifically docosapentaenoic acid (OR = 0.16, 95% CI: 0.03, 0.83) and docosahexaenoic acid (OR = 0.23, 95% CI: 0.06, 0.86), was associated with a lower odds of IA at the baseline visit, adjusting for n-3 FA supplement use, current smoking, RF+, elevated CRP+ and shared epitope. We followed 35 of the anti-CCP3+ subjects who were IA negative at baseline and detected 14 incident IA cases over an average of 2.56 years of follow-up. In a time-varying survival analysis, increasing docosapentaenoic acid significantly decreased risk of incident IA (hazard ratio = 0.52, 95% CI: 0.27, 0.98), adjusting for age at baseline, n-3 FA supplement use, RF+, CRP+ and shared epitope., Conclusion: n-3 FAs may potentially lower the risk of transition from anti-CCP positivity to IA, an observation that warrants further investigation., (© The Author 2017. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: journals.permissions@oup.com)

Objective: Studies suggest that circulating type I interferon (IFN) may predict response to biological agents in rheumatoid arthritis (RA). Prediction of response prior to initiating therapy would represent a major advancement., Methods: We studied sera from a test set of 32 patients with RA from the Auto-immune Biomarkers Collaborative Network Consortium and a validation set of 92 patients with RA from the Treatment Efficacy and Toxicity in Rheumatoid Arthritis Database and Repository registry. The test set included those with good response or no response to tumour necrosis factor (TNF) inhibitors at 14 weeks by European League Against Rheumatism criteria. The validation set included subjects with good, moderate or no response at 12 weeks. Total serum type I IFN activity, IFN-α and IFN-β activity were measured using a functional reporter cell assay., Results: In the test set, an increased ratio of IFN-β to IFN-α (IFN-β/α activity ratio) in pretreatment serum associated with lack of response to TNF inhibition (p=0.013). Anti-cyclic citrullinated peptide antibody titre and class of TNF inhibitor did not influence this relationship. A receiver-operator curve supported a ratio of 1.3 as the optimal cut-off. In the validation set, subjects with an IFN-β/α activity ratio >1.3 were significantly more likely to have non-response than good response (OR=6.67, p=0.018). The test had 77% specificity and 45% sensitivity for prediction of non-response compared with moderate or good response. Meta-analysis of test and validation sets confirmed strong predictive capacity of IFN-β/α activity ratio (p=0.005)., Conclusions: Increased pretreatment serum IFN-β/α ratio strongly associated with non-response to TNF inhibition. This study supports further investigation of serum type I IFN in predicting outcome of TNF inhibition in RA., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/)

Immune tolerance established during the development of B lymphocytes can be subverted in mature cells and lead to autoimmunity. This study focuses on the recently discovered subset of CD19(+)CD27(-)IgD(+)IgM(low/-) B cells that recognize self-antigens and have the capacity to produce autoantibodies, but under normal conditions do not generate autoimmune response due to intrinsic signaling inhibition (a condition known as clonal anergy and characterized by impaired antigen receptor signaling). Phosphorylation of intracellular signaling proteins and Ca(2+) responses in anergic B cells were measured by multicolor flow cytometry. Our results demonstrate a distinct phosphorylation pattern for major signal transduction proteins, which distinguishes anergic B cells. Comparison of B cell signaling properties in Rheumatoid Arthritis patients and healthy controls revealed a reversal of pTyr and Ca(2+) anergic signaling features in patients, accompanied by phosphorylation decreases of Blnk, Syk, SHP2, CD19. We identified BCR signaling pathway alterations associated with the loss of anergic B cell tolerance in Rheumatoid Arthritis., (Published by Elsevier Ltd.)

Objective: To evaluate the presence of pulmonary abnormalities in rheumatoid arthritis (RA)-related autoantibody-positive subjects without inflammatory arthritis., Methods: Forty-two subjects who did not have inflammatory arthritis but were positive for anti-cyclic citrullinated peptide antibodies and/or ≥2 rheumatoid factor isotypes (a profile that is 96% specific for RA), 15 autoantibody-negative controls, and 12 patients with established seropositive early RA (<1-year duration) underwent spirometry and high-resolution computed tomography (HRCT) lung imaging., Results: The median age of autoantibody-positive subjects was 54 years, 52% were female, and 38% were ever-smokers; these characteristics were not significantly different from those of autoantibody-negative control subjects. No autoantibody-positive subject had inflammatory arthritis based on joint examination. HRCT revealed that 76% of autoantibody-positive subjects had airways abnormalities including bronchial wall thickening, bronchiectasis, centrilobular opacities, and air trapping, compared with 33% of autoantibody-negative controls (P = 0.005). The prevalence and type of lung abnormalities among autoantibody-positive subjects were similar to those among patients with early RA. In 2 autoantibody-positive subjects with airways disease, inflammatory arthritis classifiable as articular RA developed ∼13 months after the lung evaluation., Conclusion: Airways abnormalities that are consistent with inflammation are common in autoantibody-positive subjects without inflammatory arthritis and are similar to airways abnormalities seen in patients with early RA. These findings suggest that the lung may be an early site of autoimmune-related injury and potentially a site of generation of RA-related autoimmunity. Further studies are needed to define the mechanistic role of lung inflammation in the development of RA., (Copyright © 2012 by the American College of Rheumatology.)

Susac syndrome (SS) consists of a triad of vision loss, hearing loss, and encephalopathy due to autoimmune-mediated vascular endothelial injury. Herein we describe a 25-year-old previously healthy woman who presented at 20 weeks' gestation with symptoms of confusion, difficulty walking, and vision and hearing loss. She had branch-retinal artery occlusions on funduscopic examination, and sensorineural hearing loss. Additionally, non-contrast enhanced brain magnetic resonance imaging showed multiple white matter and callosal lesions consistent with ischemia. She was treated initially with aspirin, corticosteroids, and intravenous immunoglobulin with early improvement, although recurrent disease was treated with cyclophosphamide and rituximab after induction of premature delivery (at 35 weeks' gestation) to spare the fetus possible toxicity. We additionally discuss a general overview of SS, what is known about pregnancy and this disease, and issues regarding diagnostic and treatment approaches for SS during pregnancy.

Objective: To identify individuals with undiagnosed inflammatory arthritis (IA) and rheumatoid arthritis (RA) in a community health fair screen, and to establish in a health fair setting the diagnostic accuracy of combinations of the Connective Tissue Disease Screening Questionnaire (CSQ) and autoantibody testing for IA., Methods: Screening for IA/RA was performed at health fair sites using a combination of the CSQ, joint examination, rheumatoid factor, and anti-cyclic citrullinated peptide (anti-CCP) antibody testing. IA was defined as > or =1 swollen joint suggestive of synovitis on joint examination by a trained clinician., Results: Six hundred one subjects were screened; 51.0% participated because of joint symptoms (pain, stiffness, or swelling). Eighty-four subjects (14.0%) had > or =1 swollen joint, designated as IA on joint examination. Of the 601 subjects screened, 9 (1.5%) had IA and met > or =4 of 7 American College of Rheumatology criteria for RA but had no prior diagnosis of RA, and 15 (2.5%) had IA and RF and/or anti-CCP positivity, suggesting early RA. The diagnostic accuracy of combinations of the CSQ and autoantibody testing for the identification of IA yielded maximal sensitivity, specificity, and positive and negative predictive values of 95.3%, 99.2%, 71.4%, and 97.7%, respectively., Conclusion: Health fair screening may be an effective approach for the identification of individuals with undiagnosed IA/RA. A combination of the CSQ and autoantibody testing alone has clinically useful diagnostic accuracy for the detection of IA. Decisions regarding which methodology to use for future health fair IA/RA screening will depend on goals of screening and funding.

The T cell receptor (TCR) repertoires of 24 human immunodeficiency virus (HIV) type 1-infected children were determined by flow cytometry in combination with sequencing of the highly variable TCR complementarity-determining region 3, permitting a quantitative and qualitative assessment of TCR repertoire. Expanded subsets of CD8(+) cells expressing a particular TCR beta-chain variable region were more commonly identified in HIV-1-infected children than in healthy control subjects (75% vs. 13.5%; P<.0001). Older age and lower percentage of CD4(+) cells were correlated with expansions. Oligoclonal populations occupied 71%-95% of each expanded subset, and predominant clones had high absolute counts. There was evidence of functional differentiation to CD28(-) effector cytotoxic T lymphocytes, and cells bearing identical TCRs were identified in both CD28(+) and CD28(-) cell populations. HIV-1 specificity was observed for expanded clones. Children with expansions were not more likely to have increased numbers of CD8(+) T cells, a finding consistent with the possibility that the CD8(+) TCR repertoire has limited diversity.

The role of T cells in the pathogenesis of rheumatoid arthritis (RA), especially in the perpetuation of advanced disease, remains unclear. Previous studies have focused on the TCR repertoire of synovial T cells in an attempt to determine whether the pattern of expression is characteristic of Ag-stimulated populations. However, the results of past studies have been conflicting. In the present work, we have undertaken an extensive analysis of the TCRs expressed by CD4+ T cells freshly isolated from synovial fluid of different joints and blood in three patients with established RA. Despite marked heterogeneity of synovial TCR expression, the results showed that 20 to 30% of the TCR beta-chain gene (TCRB) sequences found in one joint were also expressed in a second joint, but not in peripheral blood T cells of the same individual. Analysis of expressed TCRB complementarity-determining region 3 sequences showed the presence of multiple expanded clonal populations that were not predicted by quantitation of beta-chain variable region (Vbeta) expression by immunofluorescence staining. These studies also demonstrated sets of related, but different, complementarity-determining region 3 nucleotide sequences that encoded identical or highly homologous beta-chain amino acid sequences. Analysis of matching T cell clones derived from the joint by limiting dilution culture confirmed coexpression of highly homologous TCR alpha-chain gene (TCRA) and TCRB sequences. Together, these studies suggest that a significant proportion of synovial CD4+ T cells has been selected and expanded by conventional Ag(s) in this disease.

LPS-stimulated B cells were used to generate a panel of mAb that were a random sample of the preimmune repertoire of C57BL/6 and highly autoimmune, viable motheaten mice. These mAb were tested for reactivity to a number of "self" and foreign Ag. Binding that could be detected only at nM mAb concentrations or less was considered significant. We found that a surprisingly high number of the mAb bound one or more of the Ag tested, and many mAb bound more than a single Ag. Ag-induced mAb were likewise tested and found to have greatly reduced cross-reactivities. We found no significant differences, either in frequency of Ag binding or degree of cross-reactivity, between normal and autoimmune mice. Furthermore, the frequency with which a given Ag was bound by our panel of mAb was found to be proportional to the size of the Ag. The frequency with which individual VH gene families were expressed by our panel was consistent with a stochastic usage of VH genes in the preimmune repertoire. We interpret these data as showing that the preimmune repertoire is highly cross-reactive and that the activation of autoreactive clones in autoimmune animals is due to a defect in cellular regulation rather than a difference in repertoire.