Interferon‐regulated chemokines as biomarkers of systemic lupus erythematosus disease activity: A validation study

Objective

Systemic lupus erythematosus (SLE) is a complex autoimmune disease characterized by unpredictable flares of disease activity and irreversible damage to multiple organ systems. An earlier study showed that SLE patients carrying an interferon (IFN) gene expression signature in blood have elevated serum levels of IFN‐regulated chemokines. These chemokines were associated with more‐severe and active disease and showed promise as SLE disease activity biomarkers. This study was designed to validate IFN‐regulated chemokines as biomarkers of SLE disease activity in 267 SLE patients followed up longitudinally.

Methods

To validate the potential utility of serum chemokine levels as biomarkers of disease activity, we measured serum levels of CXCL10 (IFNγ‐inducible 10‐kd protein), CCL2 (monocyte chemotactic protein 1), and CCL19 (macrophage inflammatory protein 3β) in an independent cohort of 267 SLE patients followed up longitudinally over 1 year (1,166 total clinic visits).

Results

Serum chemokine levels correlated with lupus activity at the current visit (P = 2 × 10⁻¹⁰), rising at the time of SLE flare (P = 2 × 10⁻³) and decreasing as disease remitted (P = 1 × 10⁻³); they also performed better than the currently available laboratory tests. Chemokine levels measured at a single baseline visit in patients with a Systemic Lupus Erythematosus Disease Activity Index of ≤4 were predictive of lupus flare over the ensuing year (P = 1 × 10⁻⁴).

Conclusion

Monitoring serum chemokine levels in SLE may improve the assessment of current disease activity, the prediction of future disease flares, and the overall clinical decision‐making.

     

PTPN22: setting thresholds for autoimmunity

The 620W allelic variant of the intracellular tyrosine phosphatase, PTPN22, is associated with a number of different autoimmune disorders, and this provides direct evidence for common mechanisms underlying many of these diseases. The associated allele appears to influence thresholds for T cell receptor signaling, and a variety of disease models involving both central and peripheral tolerance can be proposed. However, given the fact that PTPN22 is expressed in a variety of immunologically relevant cell types, the precise mechanisms for these associations remain unclear. In general, the PTPN22 620W allele appears to play a role in autoimmune disorders that have a prominent humoral component, suggesting that further investigation of PTPN22 activity in B cells will be useful. From a genetic perspective, the data highlights the genetic heterogeneity underlying autoimmunity in different ethnic groups.     

Expression levels for many genes in human peripheral blood cells are highly sensitive to ex vivo incubation

Monitoring of gene and protein expression in peripheral blood cells has significant potential for improving the diagnosis and therapy of many human diseases. As genomic-scale microarray and proteomic technologies are applied to peripheral blood, it is important to consider the variables that may affect interpretation of data. Here we report experiments performed to identify genes that are particularly sensitive to ex vivo handling prior to RNA extraction for gene expression microarrays or quantitative real-time RT-PCR assays. We examined Affymetrix gene expression in samples from eight normal individuals where blood was processed for RNA either immediately after blood draw or the next day following overnight incubation. These studies identified hundreds of genes that are sensitive to ex vivo handling of blood, and suggest that this is an important variable to consider when designing and interpreting human PBMC experiments.     

Regulation of anti-cyclic citrullinated peptide antibodies in rheumatoid arthritis: contrasting effects of HLA-DR3 and the shared epitope alleles

OBJECTIVE: To examine the association between HLA-DRB1 alleles and the production of anti-cyclic citrullinated peptide (anti-CCP) and rheumatoid factor (RF) autoantibodies in patients with rheumatoid arthritis (RA). METHODS: We studied 1,723 Caucasian RA patients enrolled in the North American Rheumatoid Arthritis Consortium (NARAC) family cohort and the Study of New Onset Rheumatoid Arthritis (SONORA) cohort. All patients were tested for anti-CCP antibodies (by enzyme-linked immunosorbent assay), RF (by nephelometry), and HLA-DR genotype (by polymerase chain reaction and sequence-specific oligonucleotide hybridization). RESULTS: When controlled for the presence of RF, anti-CCP positivity was strongly associated with the HLA-DRB1 shared epitope (SE). In RF+ patients, the presence of the SE was very significantly associated with anti-CCP positivity, with an odds ratio (OR) of 5.8 and a 95% confidence interval (95% CI) of 4.1-8.3. This relationship was also seen in RF- patients (OR 3.1 [95% CI 1.8-5.3]). In contrast, RF positivity was not significantly associated with presence of the SE independently of anti-CCP antibodies. Strikingly, HLA-DRB1*03 was strongly associated with reduced anti-CCP titers, even after controlling for the presence of the SE and restricting the analysis to anti-CCP+ patients. HLA-DR3 was also associated with anti-CCP- RA in our population. CONCLUSION: The HLA-DRB1 SE is strongly associated with the production of anti-CCP antibodies, but not RF. In contrast, HLA-DR3 alleles are associated with anti-CCP- disease and with lower levels of anti-CCP antibodies, even when controlling for the SE. These data emphasize the complexity of the genetic effects of the major histocompatibility complex on the RA phenotype.     

Oligoclonality of CD8 + T cells in health and disease: Aging, infection, or immune regulation?

Oligoclonality of the CD8 + T cell subset is a common and characteristic feature of the normal human peripheral T cell repertoire. These clonally expanded populations are predominantly found in a CD57+ or CD28- CD8+ T cell subset. While CDS Oligoclonality is somewhat more common in the older age group, it is also very prevalent in young to middle-aged adults. Recent experiments have also demonstrated that the clonally expanded populations may actually occur in two distinct subpopulations of CD8+ CD28- cells, distinguished by the expression of the CD57 surface marker. A major difficulty with studies involving CD8+ CD28- CD57+ T cells is their relative lack of proliferative capacity. We have recently investigated the possibility that this phenotype may be due to a state of “replicative senescence” in some cases. In this regard, we have demonstrated that the telomere lengths of CD8+ CD28- T cells are generally shorter than that of their CD8+ CD28+ counterparts, consistent with a distinct replicative history for the CD8 + CD28− population. Additional studies of the normal biology of clonally expanded CD8+ T cells are likely to yield important insights into immune function in health and disease.