Association analysis in a Latin American population revealed ethnic differences in rheumatoid arthritis-associated SNPs in Caucasian and Asian populations

Large genome-wide association studies (GWAS) have increased our knowledge of the genetic risk factors of rheumatoid arthritis (RA). However, little is known about genetic susceptibility in populations with a large admixture of Amerindian ancestry. The aim of the present study was to test the generalizability of previously reported RA loci in a Latin American (LA) population with admixed ancestry. We selected 128 single nucleotide polymorphisms (SNPs) in linkage equilibrium, with high association to RA in multiple populations of non-Amerindian origin. Genotyping of 118 SNPs was performed in 313 RA patients/487 healthy control subjects by mid-density arrays of polymerase chain reaction (PCR). Some of the identified associations were validated in an additional cohort (250 cases/290 controls). One marker, the SNP rs2451258, located upstream of T Cell Activation RhoGTPase Activating Protein (TAGAP) gene, showed significant association with RA (p = 5 × 10-3), whereas 18 markers exhibited suggestive associations (p < 0.05). Haplotype testing showed association of some groups of adjacent SNPs around the signal transducer and activator of transcription 4 (STAT4) gene (p = 9.82 × 10-3 to 2.04 × 10-3) with RA. Our major finding was little replication of previously reported genetic associations with RA. These results suggest that performing GWAS and admixture mapping in LA populations has the potential to reveal novel loci associated with RA. This in turn might help to gain insight into the 'pathogenomics' of this disease and to explore trans-population differences for RA in general.

The role of interleukin-6 signalling and its therapeutic blockage in skewing the T cell balance in rheumatoid arthritis

Therapeutic blockage of cytokine signalling in autoimmune diseases has improved our understanding of the role of these cytokines in triggering, shaping and perpetuating autoimmune responses. In rheumatoid arthritis (RA), immunopathology is driven by a predominance of arthritogenic T helper cells secreting interferon-γ [T helper type 1 (Th1)] and interleukin (IL)-17 (Th17) over regulatory T cells (T_reg ). The pleiotropic cytokine IL-6 is crucial to the differentiation of Th17 cells and the balance between pathogenic Th17 and protective T_reg . Targeting the IL-6 receptor (IL-6R) by humanized antibodies improves signs and symptoms of RA, and has provided new insights into the mechanisms of inflammation and immune regulation. Here we review current evidence on the role of IL-6 in the pathogenesis of RA and the molecular consequences of IL-6R blockage in disease, with special focus on the Th17/T_reg balance and plasticity.

Effect of interleukin-6 receptor blockade on the balance between regulatory T cells and T helper type 17 cells in rheumatoid arthritis patients

A new paradigm has emerged relating the pathogenesis of rheumatoid arthritis (RA), focused on the balance between T helper type 17 cells and regulatory T cells (T(regs) ). In humans, both subpopulations depend on transforming growth factor (TGF)-β for their induction, but in the presence of inflammatory cytokines, such as interleukin (IL)-6, the generation of Th17 is favoured. Tocilizumab is a therapeutic antibody targeting the IL-6 receptor (IL-6R), which has demonstrated encouraging results in RA. The aim of this study was to evaluate the effect of tocilizumab on Th1 cells, Th17 cells, IL-17 and interferon (IFN)-γ double secretors Th17/Th1 cells, and T(regs) in RA patients. Eight RA patients received tocilizumab monthly for 24 weeks and blood samples were obtained every 8 weeks to study T cell populations by flow cytometry. The frequency of Th17 cells, Th1 cells and Th17/Th1 cells was evaluated in peripheral blood mononuclear cells (PBMCs) activated in vitro with a polyclonal stimulus. T(regs) were identified by their expression of forkhead box protein 3 (FoxP3) and CD25 by direct staining of PBMCs. Although no changes were detected in the frequency of Th1 or Th17 cells, the percentages of peripheral T(regs) increased after therapy. In addition, the infrequent Th17/Th1 subpopulation showed a significant increment in tocilizumab-treated patients. In conclusion, tocilizumab was able to skew the balance between Th17 cells and T(regs) towards a more protective status, which may contribute to the clinical improvement observed in RA patients.

Basal anti-cyclic citrullinated peptide (anti-CCP) antibody levels and a decrease in anti-CCP titres are associated with clinical response to adalimumab in rheumatoid arthritis

OBJECTIVE

To investigate the effect of adalimumab treatment on anti-cyclic citrullinated peptide antibodies (anti-CCP) in patients with rheumatoid arthritis (RA).

METHODS

70 RA patients who failed treatment with disease modifying antirheumatic drugs (DMARDs) received 40 mg adalimumab subcutaneously every other week during 24 weeks. Serum samples were collected at baseline and at weeks 8, 16 and 24 before the corresponding adalimumab dose. The serum anti-CCP levels were tested by enzyme linked immunosorbent assay.

RESULTS

At baseline, 52 of the 70 patients (74.3%) were positive for anti-CCP antibodies. 60 % of the anti CCP positive patients and 44.4% of the anti CCP negative patients were ACR 20 responders at week 24 (p<0.049). The serum levels of anti-CCP antibodies decreased significantly after 24 weeks of adalimumab treatment only in those patients who met ACR 20 response criteria at week 24 (p<0.00044). Differences between baseline anti-CCP titers and those at 8, 16 and 24 weeks were all statistically significant (p<0.014, 0.003 and 0.019 respectively). No statistically significant changes in the anti-CCP levels were observed in patients who did not meet the ACR 20 response criteria.

CONCLUSION

Basal anti-CCP antibodies levels correlate with clinical response to adalimumab. A decrease in anti-CCP levels on time was observed in patients showing also clinical improvement, suggesting that serum anti-CCP antibodies determination may be useful in assessing treatment efficacy in RA patients.

Modulation of established murine collagen-induced arthritis by a single inoculation of short-term lipopolysaccharide-stimulated dendritic cells

BACKGROUND

The use of regulatory or immature dendritic cells (DCs) as tools for modulating experimental rheumatoid arthritis is very recent. Tumour necrosis factor (TNF)-stimulated DCs have been shown to restore tolerance in experimental autoimmune encephalomyelitis and collagen-induced arthritis (CIA).

OBJECTIVE

We investigated the capacity of short-term lipopolysaccharide (LPS)-stimulated DCs pulsed with type II collagen (CII) to induce tolerance against established CIA.

METHODS

Bone marrow-derived DCs were generated in the presence of granulocyte monocyte colony-stimulating factor (GM-CSF). After CIA induction, mice were injected at day 35 with a single dose of 4- or 24-h LPS-stimulated DCs that had been loaded with CII (4hLPS/CII/DCs or 24hLPS/CII/DCs). Arthritis progression was monitored by clinical and histological evaluations.

RESULTS

Flow cytometry of 4hLPS/CII/DCs showed intermediate CD40 and CD86 expression, lower than that of 24hLPS/CII/DCs (fully mature) and higher than that of CII/DCs (immature). A functional assay showed that 4hLPS/CII/DCs display increased endocytosis ability with respect to 24hLPS/CII/DCs, indicating a semimature state. The single inoculation of 4hLPS/CII/DCs in mice with established CIA reduced disease severity significantly over time. Histological evaluation of mice treated with 4hLPS/CII/DCs revealed diminished inflammatory synovitis, cartilage damage and fibrosis. Co-cultures of DCs with splenocytes from CIA mice showed that collagen-specific interferon (IFN)gamma production was dramatically inhibited by 4hLPS/CII/DCs. 4hLPS/CII/DCs were high IL10 producers, which could explain the inhibition of arthritis progression in mice receiving this treatment because neither antibodies nor regulatory CD4+CD25+Foxp3+ T lymphocytes were demonstrated to be involved.

CONCLUSION

Short-term LPS-modulated DCs inoculation interferes with CIA progression when loaded with CII.

Tumour necrosis factor (TNF)alpha -308 G/G promoter polymorphism and TNFalpha levels correlate with a better response to adalimumab in patients with rheumatoid arthritis

OBJECTIVE

To investigate the influence of -308 tumour necrosis factor-alpha (TNFalpha) promoter polymorphism and circulating TNFalpha levels in the clinical response to adalimumab treatment in patients with rheumatoid arthritis (RA).

METHODS

Eighty-one patients with active RA were genotyped for the -308 TNFalpha polymorphism by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis and subdivided into two groups for each polymorphism (G/A and G/G genotype). All received 40 mg of adalimumab subcutaneously every other week. We compared the groups' clinical responses to adalimumab at 8, 16, and 24 weeks using the Disease Activity Score in 28 joints (DAS28).

RESULTS

Both groups showed a significant improvement from baseline. A significant difference between groups was found at week 24. We found that 88.2% of G/G versus 68.4% of G/A for the -308 polymorphism were DAS28 responders (p = 0.05). The score improvement at week 24 was 2.5 +/- 1.3 in the G/G group and 1.8 +/- 1.3 in the G/A group for the -308 polymorphism (p = 0.04). The median of serum TNFalpha levels of the G/A group were lower than those of the G/G group, and statistically different at weeks 8 and 24 (p < 0.039 and p < 0.043). When comparing baseline levels to those achieved at 8, 16, and 24 weeks for the whole group, only responder patients showed a statistically significant overall increase in TNFalpha over time (p < 0.000001).

CONCLUSION

A relationship between DAS28 improvement, the -308 G/G polymorphism, and increased circulating TNFalpha levels was found in Chilean RA patients treated with adalimumab.

Tumour necrosis factor-alpha (TNF-alpha) levels and influence of -308 TNF-alpha promoter polymorphism on the responsiveness to infliximab in patients with rheumatoid arthritis

OBJECTIVE

To investigate the influence of -308 tumour necrosis factor-alpha (TNF-alpha) promoter polymorphism and circulating TNF-alpha levels in the clinical response to the infliximab treatment in patients with rheumatoid arthritis (RA).

METHODS

One hundred and thirty-two RA patients were genotyped for TNF-alpha promoter by polymerase-chain reaction restriction fragment-length polymorphism (PCR-RFLP) analysis. Ten patients with the -308 TNF-alpha gene promoter genotype G/A, and 10 with the G/G genotype were selected and received 3 mg/kg of infliximab at Weeks 0, 2, 6, and 14.

RESULTS

Both groups showed a significant improvement with treatment in all variables studied. Total mean TNF-alpha levels increased significantly with respect to basal levels in most of patients after treatment [probability (p)=0.04]. Only patients from G/A showed a statistically significant correlation between ACR 50 and the increase of TNF-alpha levels (p<0.03).

CONCLUSION

A relationship was detected between ACR criteria of improvement and increased circulating TNF-alpha levels in RA patients subjected to anti-TNF-alpha therapy.

The -308 polymorphism in the tumour necrosis factor (TNF) gene promoter region and ex vivo lipopolysaccharide-induced TNF expression and cytotoxic activity in Chilean patients with rheumatoid arthritis

OBJECTIVE

To investigate the association of the -308 polymorphism in the promoter region of the tumour necrosis factor (TNF) gene with susceptibility to the development of RA. We also explored the expression and cytotoxicity of TNF in relation to the -308 polymorphism.

METHODS

We recruited 92 RA patients and 42 healthy control subjects. Genotyping for the TNF promoter was performed by polymerase chain reaction-restriction fragment length polymorphism analysis. To study the overexpression of TNF we used a whole-blood culture system. TNF cytotoxicity was assessed in the L929 cell line.

RESULTS

The TNF2 allele was found in 23% of RA patients and 10% of controls. Although both groups showed high variability in serum TNF concentration, in the lipopolysaccharide-induced TNF level and in the cytotoxicity of the cytokine in the L929 cell line, these differences were not associated with the -308 TNF polymorphism.

CONCLUSION

No associations were found between the -308 TNF promoter polymorphism, serum and ex vivo TNF levels and the cytotoxic activity of TNF in RA patients.

Genetic polymorphism at position-308 in the promoter region of the tumor necrosis factor (TNF): implications of its allelic distribution on susceptibility or resistance to diseases in the Chilean population

Several single-nucleotide polymorphisms have been identified in the human TNF gene promoter. The polymorphism at position-308 (TNF-308), which involves substituting G for A and designing the TNF2 allele, leads to a higher rate of TNF gene transcription than the wild-type TNF1 allele in in vitro expression studies. It has also been linked to increased susceptibility to a variety of illnesses. Using PCR-RFLP analysis we detected significant differences in the TNF-308 genotypes of Chilean and other populations. We conclude that there is a gradient in the distribution of the TNF2 allele according to ethnicity; we have also hypothesized that populations bearing a higher proportion of the TNF2 allele may have an increased predisposition toward or incidence of several chronic metabolic, degenerative, inflammatory and autoimmune diseases.

Daily production of human tumor necrosis factor in lipopolysaccharide (LPS)-stimulated ex vivo blood culture assays

Tumor necrosis factor (TNF) is a pleiotropic cytokine with immunological and neuroendocrine activities. A useful tool for studying TNF is the measurement of its in vitro and/or ex vivo over-expression, induced by a variety of stimuli on isolated peripheral mononuclear cells or whole blood, respectively. The capacity to over-express TNF, in ex vivo LPS-stimulated whole blood from 18 normal individuals, showed inter-individual variations ranging from high (3 ng/ml) to low (0.7 ng/ml) producers. Although at a lower level, a similar situation was observed in the spontaneous production of the cytokine. In order to detect cyclic effects in these variations, blood samples were taken at 08:00, 12:00, 16:00 and 20:00 hours, from nine healthy volunteers, and cultured in the ex vivo system. TNF and cortisol were measured by immunometric assays. Both, LPS-stimulated whole blood and plasma showed important, individual variations in TNF levels. Although cortisol levels presented a normal circadian cycle, these individual patterns in TNF production were basically conserved during the day (p > 0.05), and no correlation was observed between the levels of the hormone and those of the cytokine. When total TNF levels were determined at 20:00 hours, a moderate, temporary variation pattern of the cytokine production was found. These results suggest that cortisol does not play a predominant role in determining the ex vivo capacity of blood to produce TNF. Presumably, the variable capacity to produce the cytokine may have a strong genetic component.

Tc45, a dimorphic Trypanosoma cruzi immunogen with variable chromosomal localization, is calreticulin

We demonstrate that Tc45, a polypeptide described as an immunogenetically restricted Trypanosoma cruzi antigen in mice, is calreticulin, a dimorphic molecule encoded by genes with variable chromosomal distribution. Previously we showed that IgG from A.SW (H2s) mice immunized with T. cruzi trypomastigotes or epimastigotes and sera from infected humans recognize Tc45, a 45 kD parasite polypeptide. Herein we describe the cloning, sequencing, and expression of the Tc45 gene. A 98% homology in the deduced amino acid sequence was found with a T. cruzi calreticulin-like molecule and 41% with Leishmania donovani and human calreticulin. In the T. cruzi CL Brener clone and in the Tulahuén strain, the gene is located in two and four chromosomes, respectively. Calreticulin was detected in several T. cruzi clones, in the Tulahuén strain, and in T. rangeli, displaying alternative 43 and 46 kD forms.

Trypanosoma cruzi: H2 complex and genetic background influence on the humoral immune response against epimastigotes

Using A.SW, A.CA, B10.S and B10.M congenic mouse strains, we measured the IgG specific humoral immune responses against sonicated and live Trypanosoma cruzi epimastigotes. Genes located in the A background (A.SW and A.CA strains) mediate higher IgG responses against the parasite antigenic complexes than those located in the B background (strains B10.S and B10.M), regardless of the H2 haplotypes. Thus, non H2 genetic elements seem to be more important in determining differences in the total IgG immune response against T. cruzi. Whether a detectable H2 effect, in favor of the H2(s) haplotype, occurred in the A or B background, was contingent on the immunisation protocol used. Thus, the H2(s) haplotype mediates a higher IgG response in the A background, if immunised with live epimastigotes, and in the B background against sonicated epimastigotes. Most likely this represents a complex sequence of events, controlled by non-MHC genes, involving antigen handling and processing and depending on the physical form of antigen delivery.

Development of an immunoenzymatic assay for the detection of human antibodies against Trypanosoma cruzi calreticulin, an immunodominant antigen

We have developed an indirect immunoenzymatic assay (ELISA) for the detection of human antibodies against calreticulin (formerly known as Tc45), a dimorphic Trypanosoma cruzi antigen, described in our laboratory. PVC microtitration plates were sensitized with the monoclonal anti-calreticulin antibody (MoAb) and reacted with calreticulin present in a partially purified preparation. The presence of anti-T. cruzi calreticulin IgG in sera from infected individuals was tested. The data generated with this assay were validated by correlation, in a regression analysis, with those obtained by an indirect immunoradiometric assay (IRMA). From the 12 seropositive sera (as defined by a commercial test), eight came out positive and four negative in both assays. The 12 human sera were also analyzed in direct immunometric assays (ELISA and IRMA), where the solid phase was sensitized with a whole parasite extract. The direct ELISA and IRMA correlated positively (P<0.01). Further validation of this ELISA was achieved with an indirect immunofluorescense assay. The high degree of significance obtained when the indirect IRMA and ELISA systems were compared, indicated that the relatively small sample number used (12) was statistically satisfactory for the purposes of this investigation. Thus, the IRMA can be replaced by the ELISA, with advantages mainly derived from the cumbersome manipulation of radioactive wastes. The MoAb used as an antigen capture agent in the ELISA proposed here, recognizes a homologous protein in Trypanosoma rangeli, suggesting that individuals infected with this parasite might have crossreactive antibodies. However, the system retains its diagnostic interest, given the facts that the MoAb does not recognize a homologous protein in Leishmania mexicana, Leishmania donovani, or Crithidia fasciculata.

Immunodiagnosis of fasciolosis in horses and pigs using western blots

Crude and partially purified somatic (S) and excretory-secretory (ES) antigens of Fasciola hepatica were subjected to Western blot analysis in order to identify polypeptides that would enable specific and sensitive immunodiagnosis of horse and pig fasciolosis to be undertaken. Sera from 20 horses and 20 pigs with natural infections of F. hepatica and the same number of uninfected hosts of each species were tested, together with sera from 2 pigs with Cysticercus cellulosae infections. Using crude S antigens, sera from infected horses and pigs reacted specifically with a wide range of polypeptides of 14-19, 22-30, 35-37 and 42 kDa. Likewise, specific reactivity between polypeptides of 14-17, 22-30 and 40-42 kDa in crude ES antigens and sera from infected horses and pigs was obtained. Against the criteria of high sensitivity and specificity, the 22-30-kDa polypeptides would appear to be the most suitable candidate antigens for use in the immunodiagnosis of fasciolosis in horses and pigs.

Recognition of an immunogenetically selected Trypanosoma cruzi antigen by seropositive chagasic human sera

If the H-2 congenic mouse strains A.SW (H-2n) and A.CA (H-2f), are infected with Trypanosoma cruzi, a 45 kDa protein (Tc45), present in cultured epimastigotes and blood trypomastigotes, is recognized only by the A.SW strain sera. In order to explore the possibility that among seropositive humans the response to Tc45 is also highly variable, 81 chagasic human sera (as defined by the HemAve agglutination test, Polychaco S.A.I.C., Buenos Aires, Argentina) were tested in a direct (epimastigote antigenic complex directly bound to the solid phase) and indirect immunoradiometric assay (IRMA) (Tc45, from a partially purified preparation, bound to the solid phase, by means of a monoclonal antibody). Sixty nine of these sera reacted in both the direct and indirect assays, 11 were negative in both assays (these samples may correspond to false positives detected by the commercial agglutination test) and only one reacted with the antigenic complex but not with Tc45. Reactivity of the human sera with the epimastigote antigenic extract was relatively homogenous, while reactivity with Tc45 was extremely variable. No statistical correlation was determined between the two variables. Given the high variability of the human response to Tc45, ranging from negative to highly positive, together with the immunogenetic restriction previously described in the murine model, we speculate that human MHC may also modulate the response to this molecule.

Immunomodulation of LPS ability to induce the local Shwartzman reaction

Immunologically, the septic shock is a natural model of immunomediated vascular pathology where the interaction between cytokines and the endothelium mediates the syndrome and lethality. Tumour necrosis factor (TNF), a non-species-specific cytokine, has outstanding pleiotropic activities as an important mediator of the septic shock syndrome. In rabbits, passive immunization with anti-lipopolysaccharide (LPS) polyclonal antibodies prior to the intravenous (i.v.) injection of LPS inhibits the haemorrhagic necrotic lesion characteristic of the local Shwartzman reaction (an excellent localized in vivo correlate of the septic shock). Paradoxically, tested in an ex vivo assay (short-term whole human blood culture, stimulated with LPS), these antibodies mediated an increase in TNF production by mononuclear phagocytes and, in the rabbit model, they induced an increase in body temperature, as compared with the pre-immune reagent. Although anchoring of immune complexes containing LPS to receptors (Fc or C4b-C3b) on circulating monocytes may facilitate the access of LPS to these cells, access to localized, LPS-sensitized macrophages may be impaired. Consequently inhibition of the local Shwartzman reaction and increased TNF production in the ex vivo system were observed. Concordantly, the higher temperature in the passively immunized animals may be a consequence of a higher, immune complex-induced, systemic TNF production. These experimental results suggest that the use of anti-LPS immunoglobulins, as a potential immunotherapy for septic shock syndrome in vertebrates, may lead to increased TNF production, with adverse effects such as the pyrogenic.

A simple method for negative and positive selection of murine and human IgM-bearing lymphocytes based on the use of antibody-coated silica microparticles

The use of octadecyl silica microparticles is proposed as an alternative method for negative and positive selection of IgM-bearing lymphocytes. SiC18 microparticles coated with affinity purified IgG anti-IgM were evaluated in their efficiency to deplete IgM-bearing cells. 6 mg of SiC18-IgG depleted an average of 97% IgM-bearing cells from a murine spleen cell suspension and of 84% IgM-bearing cells from human spleen cells. The viability of the selected cells was not affected by this procedure. We also analyzed the ability of whole serum to release IgM-bearing cells from the complex SiC18-target cell. The IgM releasing efficiency was 98%, with a resulting viability of 85%. These results indicate that SiC18 microparticles, saturated with specific antibodies, may be used as an alternative method for depletion or purification of cells bearing the corresponding antigen, from complex cell suspensions. The method is simple, efficient and inexpensive, representing an interesting alternative to the immunomagnetic selection.

Octadecyl silica: a solid phase for protein purification by immunoadsorption

Immunoaffinity chromatography involves binding of an antigen or antibody to a solid matrix, usually agarose, frequently using the cyanogen bromide method. These methods are laborious, rather expensive, and their use has been mostly restricted to immunopurifications on the microscale. We propose here the use of octadecyl silica (SiCl8) beads, a matrix for HPLC, as an alternative solid phase for protein immunopurification and immunoadsorption. Antibodies or antigens are strongly bound to SiCl8 by a simple incubation; radiolabeled antibodies can only be eluted from SiCl8 by detergent-containing solutions. After the remaining free binding sites have been saturated with bovine serum albumin, SiCl8 is incubated with the antigen- or antibody-containing crude preparations and is then poured into a minicolumn. The nonspecifically bound proteins are removed by washing; specific proteins are eluted by disruption of the antigen-antibody complexes with a low pH buffer. With this methodology, we have obtained high purity preparations of proteins in single steps, even when these proteins are present in trace amounts (picograms) in a complex mixture such as human serum. Similarly, specific antibodies against an intracellular parasite (Trypanosoma cruzi) were completely absorbed from human serum with SiCl8 coated with parasite antigens.