Antibody responses to Porphyromonas gingivalis (P. gingivalis) in subjects with rheumatoid arthritis and periodontitis.

Unlabelled: Antibody titers to P. gingivalis are increased in patients with rheumatoid arthritis and are associated with disease-specific autoimmunity.

Background: Periodontitis (PD) has been implicated as a risk factor for rheumatoid arthritis (RA).

Initiation of the alternative pathway of murine complement by immune complexes is dependent on N-glycans in IgG antibodies.

Objective: Collagen antibody-induced arthritis in mice exhibits a requirement for amplification by the alternative pathway of complement. Although the alternative pathway is activated by spontaneous hydrolysis, it is not known whether this pathway can also be initiated directly by IgG antibodies in immune complexes (ICs). IgG lacking terminal sialic acid and galactose (G0 IgG) can activate the lectin pathway of complement, but it is not known if G0 IgG can also activate the classical or alternative pathway.

Solution structure of the complex formed between human complement C3d and full-length complement receptor type 2.

Complement receptor type 2 (CR2, CD21) is a cell surface protein that links the innate and adaptive immune response during the activation of B-cells through its binding to C3d, a cleavage fragment of the major complement component C3. The extracellular portion of CR2 comprises 15 or 16 short complement regulator (SCR) domains in a partially folded-back but flexible structure. Here, the effect of C3d binding to CR2 was determined by analytical ultracentrifugation and X-ray scattering.

Molecular basis of the interaction between complement receptor type 2 (CR2/CD21) and Epstein-Barr virus glycoprotein gp350.

The binding of the Epstein-Barr virus glycoprotein gp350 by complement receptor type 2 (CR2) is critical for viral attachment to B lymphocytes. We set out to test hypotheses regarding the molecular nature of this interaction by developing an enzyme-linked immunosorbent assay (ELISA) for the efficient analysis of the gp350-CR2 interaction by utilizing wild-type and mutant forms of recombinant gp350 and also of the CR2 N-terminal domains SCR1 and SCR2 (designated CR2 SCR1-2). To delineate the CR2-binding site on gp350, we generated 17 gp350 single-site substitutions targeting an area of gp350 that has been broadly implicated in the binding of both CR2 and the major inhibitory anti-gp350 monoclonal antibody (MAb) 72A1.

The spectrum of complement alternative pathway-mediated diseases.

The complement system has once again come into prominence in the therapeutic development arena. The recent approval of an inhibitory monoclonal antibody, eculizumab, which is directed against complement component C5 for the disease paroxysmal nocturnal hemoglobinuria has provided the initial validation of this system as a therapeutic target. Preclinical studies using animal models and human-derived samples demonstrate that inhibition of complement ameliorates many inflammatory and autoimmune disease manifestations.

Evidence for non-traditional activation of complement factor C3 during murine liver regeneration.

Unlabelled: Complement signaling has been implicated as important for normal hepatic regeneration. However, the specific mechanism by which complement is activated during liver regeneration remains undefined. To address this question, we investigated the hepatic regenerative response to partial hepatectomy in wildtype mice, C3-, C4-, and factor B-null mice, and C4-null mice treated with a factor B neutralizing antibody (mAb 1379).

Complement receptor CR2/CR1 deficiency protects mice from collagen-induced arthritis and associates with reduced autoantibodies to type II collagen and citrullinated antigens.

Collagen-induced arthritis (CIA), a model of autoimmune inflammatory arthritis, depends upon complement activation and effective B cell responses. To determine the importance of complement receptors CR2/CR1 in CIA, the Cr2-/- genotype was backcrossed onto the DBA/1j strain. CIA was induced by immunization with bovine type II collagen in CFA on days 0 and 21.

The HLA-DRB1 shared epitope is associated with susceptibility to rheumatoid arthritis in African Americans through European genetic admixture.

Objective: To determine whether shared epitope (SE)-containing HLA-DRB1 alleles are associated with rheumatoid arthritis (RA) in African Americans and whether their presence is associated with higher degrees of global (genome-wide) genetic admixture from the European population.

Methods: In this multicenter cohort study, African Americans with early RA and matched control subjects were analyzed. In addition to measurement of serum anti-cyclic citrullinated peptide (anti-CCP) antibodies and HLA-DRB1 genotyping, a panel of >1,200 ancestry-informative markers was analyzed in patients with RA and control subjects, to estimate the proportion of European ancestry.

Alternative complement pathway activation fragment Bb in early pregnancy as a predictor of preeclampsia.

Objective: Preeclampsia is a multisystem disease classically defined on the basis of hypertension and proteinuria. As shown in animal studies, complement activation is associated with inflammation in the placenta and adverse pregnancy outcomes. The association between complement activation in humans and adverse pregnancy outcomes is unclear.

Complement is an essential component of the immune response to adeno-associated virus vectors.

Adeno-associated virus (AAV) vectors are associated with relatively mild host immune responses in vivo. Although AAV induces very weak innate immune responses, neutralizing antibodies against the vector capsid and transgene still occur. To understand further the basis of the antiviral immune response to AAV vectors, studies were performed to characterize AAV interactions with macrophages.

Cigarette smoking, disease severity and autoantibody expression in African Americans with recent-onset rheumatoid arthritis.

Objective: To examine the association of smoking with clinical and serological features in African Americans with recent-onset rheumatoid arthritis (RA) and to explore whether this association is dependent on the presence of the HLA-DRB1 shared epitope (SE).

Methods: In African Americans with recent-onset RA (n = 300), we examined the association of cigarette smoking (current versus past versus never and pack-years of exposure) with anti-cyclic citrullinated peptide antibody, rheumatoid factor (RF) (IgM and IgA), rheumatoid nodules and baseline radiographic erosions using logistic and cumulative logistic regression (adjusting for SE status). We also examined for evidence of interaction between smoking status and SE for all outcomes.

A complement C3 inhibitor specifically targeted to sites of complement activation effectively ameliorates collagen-induced arthritis in DBA/1J mice.

Collagen-induced arthritis (CIA) represents an animal model of autoimmune polyarthritis with similarities to human rheumatoid arthritis, and therapy with various systemic complement-inhibitory proteins has been investigated in this model with varying results. We investigated the use of complement receptor 2 (CR2)-Crry, a complement inhibitor with the ability to target C3 breakdown products deposited in a rheumatic joint. Following induction of CIA in DBA/1J mice, animals were treated with either PBS or CR2-Crry (every other day, every 4 days, or with a single injection).

Duration of preclinical rheumatoid arthritis-related autoantibody positivity increases in subjects with older age at time of disease diagnosis.

Objectives: To investigate factors that may influence the prevalence and timing of appearance of rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies during the preclinical phase of rheumatoid arthritis (RA) development.

Methods: 243 serial prediagnosis serum samples from 83 subjects with RA were examined for the presence of RF and anti-CCP antibodies.

Results: Of the 83 cases, 47 (57%) and 51 (61%) subjects had at least one prediagnosis sample positive for RF or anti-CCP, respectively.

Isolating the Epstein-Barr virus gp350/220 binding site on complement receptor type 2 (CR2/CD21).

Complement receptor type 2 (CR2/CD21) is essential for the attachment of Epstein-Barr virus (EBV) to the surface of B-lymphocytes in an interaction mediated by the viral envelope glycoprotein gp350. The heavily glycosylated structure of EBV gp350 has recently been elucidated by x-ray crystallography, and the CR2 binding site on this protein has been characterized. To identify the corresponding gp350 binding site on CR2, we have undertaken a site-directed mutagenesis study targeting regions of CR2 that have previously been implicated in the binding of CR2 to the C3d/C3dg fragments of complement component C3.

Antibodies to citrullinated proteins: pathogenic and diagnostic significance.

The recent demonstration of efficacy in the treatment of rheumatoid arthritis with B-cell-depleting therapy, along with the increasing understanding of the role of anticitrullinated protein antibodies (ACPA) have begun to provide new insights into the pathogenesis of this complex disease. This manuscript reviews the current understanding of ACPA with regard to clinical associations and pathogenic mechanisms in preclinical animal models. These data are synthesized into a model of the development of rheumatoid arthritis that refocuses attention on the role of B cells and immune complexes, returning in part to the origins of scientific investigation in this disease, and points to directions of research that are necessary to achieve the full therapeutic, diagnostic, and prognostic potential of the ACPA antigen-antibody system.

Pathogenic complement activation in collagen antibody-induced arthritis in mice requires amplification by the alternative pathway.

Immune complex-induced inflammation can be mediated by the classical pathway of complement. However, using mice genetically deficient in factor B or C4, we have shown that the collagen Ab-induced model of arthritis requires the alternative pathway of complement and is not dependent on the classical pathway. We now demonstrate that collagen Ab-induced arthritis is not altered in mice genetically deficient in either C1q or mannose-binding lectins A and C, or in both C1q and mannose-binding lectins.

Cutting edge: Complement (C3d)-linked antigens break B cell anergy.

C3dg adducts of Ag can coligate complement receptor type 2 (CR2; CD21) and the B cell Ag receptor. This interaction significantly amplifies BCR-mediated signals in Ag-naive wild-type mice, lowering the threshold for B cell activation and the generation of humoral immune responses as much as 1000-fold. In this study we demonstrate that CR2-mediated complementation of BCR signals can also overcome B cell anergy.

The alternative pathway of complement is activated in the glomeruli and tubulointerstitium of mice with adriamycin nephropathy.

The complement system effectively identifies and clears invasive pathogens as well as injured host cells. Uncontrolled complement activation can also contribute to tissue injury, however, and inhibition of this system may ameliorate many types of inflammatory injury. Several studies have demonstrated that the filtration of complement proteins into the renal tubules, as occurs during proteinuric renal disease, causes tubular inflammation and injury.

Role for CD21 in the establishment of an extracellular HIV reservoir in lymphoid tissues.

Follicular dendritic cells (FDC) represent a major extracellular reservoir for HIV. A better understanding of the mechanisms of virion attachment to FDC may offer new avenues for reducing viral burdens in infected individuals. We used a murine model to investigate the establishment of extracellular HIV reservoirs in lymph nodes (LN).

The alternative pathway of complement activation is critical for blister induction in experimental epidermolysis bullosa acquisita.

Epidermolysis bullosa acquisita is a subepidermal blistering disease associated with tissue-bound and circulating autoantibodies against type VII collagen, a major constituent of the dermal-epidermal junction. The passive transfer of Abs against type VII collagen into mice induces a subepidermal blistering disease dependent upon activation of terminal complement components. To further dissect the role of the different complement activation pathways in this model, we injected C1q-deficient, mannan-binding lectin-deficient, and factor B-deficient mice with rabbit Abs against murine type VII collagen.

Inhibition of the alternative complement activation pathway in traumatic brain injury by a monoclonal anti-factor B antibody: a randomized placebo-controlled study in mice.

Background: The posttraumatic response to traumatic brain injury (TBI) is characterized, in part, by activation of the innate immune response, including the complement system. We have recently shown that mice devoid of a functional alternative pathway of complement activation (factor B-/- mice) are protected from complement-mediated neuroinflammation and neuropathology after TBI. In the present study, we extrapolated this knowledge from studies in genetically engineered mice to a pharmacological approach using a monoclonal anti-factor B antibody.

Defective B cell ontogeny and immune response in human complement receptor 2 (CR2, CD21) transgenic mice is partially recovered in the absence of C3.

Mice prematurely expressing human CR2 (hCR2) in the B cell lineage have a defective B cell ontogeny and immune response. Our recent analysis of this phenotype suggested that signaling through hCR2 and presumably mouse CD19 on the B cell surface, during bone marrow development, could result in the observed changes in B cell function in these mice. To test this hypothesis, we back crossed hCR2(high) transgenic mice onto the CD19(-/-) background.

Guidelines for assessing immunocompetency in clinical trials for autoimmune diseases.

Clinical trials testing the safety and efficacy of immunosuppressive agents for the treatment of autoimmune diseases should also be designed to evaluate immunocompetency. The most clinically relevant outcome for assessing immunocompetency is the infection rate. Therefore, a systematic approach to screening, monitoring, and reporting infections, modeled after the recommendations of the American Society of Transplantation, is presented.

Intrinsic B cell hypo-responsiveness in mice prematurely expressing human CR2/CD21 during B cell development.

We previously reported that human CR2 (hCR2) prematurely expressed under a murine Vlambda2 promoter/Vlambda2-4 enhancer minigene during the CD43+ CD25- late pro-B cell stage of development results in peripheral B cells with impaired responses to immunization with T-dependent antigens. Herein, we show that hCR2 transgenic (Tg) mice also demonstrate a severe defect in T-independent antigen responses and are substantially protected from clinical arthritis, synovitis and cartilage/bone destruction in a collagen-induced arthritis model. This outcome is found despite the apparently normal development of autoreactive T cells with equivalent cytokine and proliferative responses to antigen when compared to non-Tg control mice.

C3a is required for the production of CXC chemokines by tubular epithelial cells after renal ishemia/reperfusion.

The complement system is one of the major ways by which the body detects injury to self cells, and the alternative pathway of complement is rapidly activated within the tubulointerstitium after renal ischemia/reperfusion (I/R). In the current study, we investigate the hypothesis that recognition of tubular injury by the complement system is a major mechanism by which the systemic inflammatory response is initiated. Gene array analysis of mouse kidney following I/R initially identified MIP-2 (CXCL2) and keratinocyte-derived chemokine (KC or CXCL1) as factors that are produced in a complement-dependent fashion.