Faculty Bibliography

OBJECTIVE: The presence of anticitrullinated protein antibodies (ACPA) in rheumatoid arthritis (RA) indicates a breach in immune tolerance. Recent studies indicate that this breach extends to homocitrullination of lysines with the formation of anti-carbamylated protein (anti-CarP) antibodies. We analyzed the clinical and serologic relationships of anti-CarP in 2 RA cohorts. METHODS: Circulating levels of immunoglobulin G anti-CarP antibodies were determined by ELISA in established (Dartmouth-Hitchcock Medical Center) and early (Sherbrooke University Hospital Center) cohorts and evaluated for anticyclic citrullinated peptide antibodies (anti-CCP), specific ACPA, and rheumatoid factor (RF) levels using the Student t test and correlation analysis. RESULTS: We identified elevated anti-CarP antibodies titers in 47.0% of seropositive patients (Dartmouth, n = 164), with relationships to anti-CCP (p < 0.0001) and IgM-RF (p = 0.001). Similarly, 38.2% of seropositive patients from the Sherbrooke cohort (n = 171) had elevated anti-CarP antibodies; titers correlated to anti-CCP (p = 0.01) but not IgM-RF (p = 0.09). A strong correlation with anti-Sa was observed: 47.9% anti-Sa+ patients were anti-CarP antibodies+ versus only 25.4% anti-Sa- in the Sherbrooke cohort (p = 0.0002), and 62.6% anti-Sa+ patients versus 26.9% anti-Sa- were anti-CarP antibodies+ in Dartmouth (p < 0.0001). We found a more variable response for reactivity to citrullinated fibrinogen or to citrullinated peptides from fibrinogen and alpha enolase. CONCLUSION: In 2 North American RA cohorts, we observed a high prevalence of anti-CarP antibody positivity. We also describe a surprising and unexpected association of anti-CarP with anti-Sa antibodies that could not be explained by cross-reactivity. Further, considerable heterogeneity exists between anti-CarP reactivity and other citrullinated peptide reactivity, raising the question of how the pathogenesis of antibody responses for carbamylated proteins and citrullinated proteins may be linked in vivo.

During murine immune development, recurrent B cell clones arise in a predictable fashion. Among these B cells, an archetypical clonotypic set that recognizes phosphorylcholine (PC) antigens and produces anti-PC IgM, first implicated for roles in microbial protection, was later found to become expanded in hyperlipidemic mice and in response to an increased in vivo burden of apoptotic cells. These IgM natural antibodies can enhance clearance of damaged cells and induce intracellular blockade of inflammatory signaling cascades. In clinical populations, raised levels of anti-PC IgM correlate with protection from atherosclerosis and may also downmodulate the severity of autoimmune disease. Human anti-PC-producing clones without hypermutation have been isolated that can similarly discriminate apoptotic from healthy cells. An independent report on unrelated adults has described anti-PC-producing B cells with IgM genes that have conserved CDR3 motifs, similar to stereotypic clonal sets of B cell chronic lymphocytic leukemia. Taken together, emerging evidence suggests that, despite the capacity to form an effectively limitless range of Ig receptors, the human immune system may often recurrently generate lymphocytes expressing structurally convergent B cell receptors with protective and homeostatic roles.

Identifying the germline genes involved in immunoglobulin rearrangements is an essential first step in the analysis of antibody repertoires. Based on our prior work in analysing diverse recombinant viruses, we present IgSCUEAL (Immunoglobulin Subtype Classification Using Evolutionary ALgorithms), a phylogenetic approach to assign V and J regions of immunoglobulin sequences to their corresponding germline alleles, with D regions assigned using a simple pairwise alignment algorithm. We also develop an interactive web application for viewing the results, allowing the user to explore the frequency distribution of sequence assignments and CDR3 region length statistics, which is useful for summarizing repertoires, as well as a detailed viewer of rearrangements and region alignments for individual query sequences. We demonstrate the accuracy and utility of our method compared with sequence similarity-based approaches and other non-phylogenetic model-based approaches, using both simulated data and a set of evaluation datasets of human immunoglobulin heavy chain sequences. IgSCUEAL demonstrates the highest accuracy of V and J assignment amongst existing approaches, even when the reassorted sequence is highly mutated, and can successfully cluster sequences on the basis of shared V/J germline alleles.

OBJECTIVES: The efficacy and safety of 2 different dosing regimens of tabalumab, a monoclonal antibody that neutralizes membrane-bound and soluble B-cell-activating factor (BAFF), were evaluated in patients with rheumatoid arthritis. METHODS: In this phase 3, multicenter, randomized study, 1004 patients (intention-to-treat population) received subcutaneous 120 mg tabalumab every 4 weeks (120/Q4W), 90 mg tabalumab every 2 weeks (90/Q2W), or placebo over 24 weeks. At baseline, a loading dose double the planned dose (ie, 240 mg, 180 mg, or placebo) was administered. Efficacy analyses were based on a prespecified subset of patients with 5 or more of 68 tender and 5 or more of 66 swollen joints at baseline (efficacy population, n = 849). The primary efficacy end point was ACR20 (20% improvement in American College of Rheumatology criteria) response at week 24. RESULTS: At week 24, there were no differences in ACR20 response rates (120/Q4W = 34.4%, 90/Q2W = 33.5%, placebo = 31.5%) or any other measures of efficacy across the treatment groups. Discontinuations due to adverse events (AE) were 3.4%, 2.7%, and 4.0%; incidence of treatment-emergent AEs were 64.1%, 58.2%, and 58.8%, with 23.2%, 25.9%, and 22.0% treatment-emergent infections; and incidence rates of serious AEs were 3.7%, 2.2%, and 2.8% with 1.1%, 0.3%, and 0.7% serious infections in the 120/Q4W, 90/Q2W, and placebo groups, respectively. Three deaths were reported (120/Q4W, n = 2; 90/Q2W, n = 1). Each tabalumab group had significant decreases versus placebo in CD3-CD20 B cells (P