Human Complement C4B Allotypes and Deficiencies in Selected Cases With Autoimmune Diseases

Human complement C4 is one of the most diverse but heritable effectors for humoral immunity. To help understand the roles of C4 in the defense and pathogenesis of autoimmune and inflammatory diseases, we determined the bases of polymorphisms including the frequent genetic deficiency of C4A and/or C4B isotypes. We demonstrated the diversities of C4A and C4B proteins and their gene copy number variations (CNVs) in healthy subjects and patients with autoimmune disease, such as type 1 diabetes, systemic lupus erythematosus (SLE) and encephalitis. We identified subjects with (a) the fastest migrating C4B allotype, B7, or (b) a deficiency of C4B protein caused by genetic mutation in addition to gene copy-number variation. Those variants and mutants were characterized, sequenced and specific techniques for detection developed. Novel findings were made in four case series. First, the amino acid sequence determinant for C4B7 was likely the R729Q variation at the anaphylatoxin-like region. Second, in healthy White subject MS630, a C-nucleotide deletion at codon-755 led to frameshift mutations in his single C4B gene, which was a private mutation. Third, in European family E94 with multiplex lupus-related mortality and low serum C4 levels, the culprit was a recurrent haplotype with HLA-A30, B18 and DR7 that segregated with two defective C4B genes and identical mutations at the donor splice site of intron-28. Fourth, in East-Asian subject E133P with anti-NMDA receptor encephalitis, the C4B gene had a mutation that changed tryptophan-660 to a stop-codon (W660x), which was present in a haplotype with HLA-DRB1*04:06 and B*15:27. The W660x mutation is recurrent among East-Asians with a frequency of 1.5% but not detectable among patients with SLE. A meticulous annotation of C4 sequences revealed clusters of variations proximal to sites for protein processing, activation and inactivation, and binding of interacting molecules.

Four Systemic Lupus Erythematosus Subgroups, Defined by Autoantibodies Status, Differ Regarding HLA-DRB1 Genotype Associations and Immunological and Clinical Manifestations

Objective

The heterogeneity of systemic lupus erythematosus (SLE) constitutes clinical and therapeutical challenges. We therefore studied whether unrecognized disease subgroups can be identified by using autoantibody profiling together with HLA‐DRB1 alleles and immunological and clinical data.

Methods

An unsupervised cluster analysis was performed based on detection of 13 SLE‐associated autoantibodies (double‐stranded DNA, nucleosomes, ribosomal P, ribonucleoprotein [RNP] 68, RNPA, Smith [Sm], Sm/RNP, Sjögren's syndrome antigen A [SSA]/Ro52, SSA/Ro60, Sjögren's syndrome antigen B [SSB]/La, cardiolipin [CL]‐Immunoglobulin G [IgG], CL–Immunoglobulin M [IgM], and β₂ glycoprotein I [β₂GPI]–IgG) in 911 patients with SLE from two cohorts. We evaluated whether each SLE subgroup is associated with HLA‐DRB1 alleles, clinical manifestations (n = 743), and cytokine levels in circulation (n = 446).

Results

Our analysis identified four subgroups among the patients with SLE. Subgroup 1 (29.3%) was dominated by anti‐SSA/Ro60/Ro52/SSB autoantibodies and was strongly associated with HLA‐DRB1*03 (odds ratio [OR] = 4.73; 95% confidence interval [CI] = 4.52‐4.94). Discoid lesions were more common for this disease subgroup (OR = 1.71, 95% CI = 1.18‐2.47). Subgroup 2 (28.7%) was dominated by anti‐nucleosome/SmRNP/DNA/RNPA autoantibodies and associated with HLA‐DRB1*15 (OR = 1.62, 95% CI = 1.41‐1.84). Nephritis was most common in this subgroup (OR = 1.61, 95% CI = 1.14‐2.26). Subgroup 3 (23.8%) was characterized by anti‐ß₂GPI‐IgG/anti‐CL–IgG/IgM autoantibodies and a higher frequency of HLA‐DRB1*04 compared with the other patients with SLE. Vascular events were more common in Subgroup 3 (OR = 1.74, 95% CI = 1.2‐2.5). Subgroup 4 (18.2%) was negative for the investigated autoantibodies, and this subgroup was not associated with HLA‐DRB1. Additionally, the levels of eight cytokines significantly differed among the disease subgroups.

Conclusion

Our findings suggest that four fairly distinct subgroups can be identified on the basis of the autoantibody profile in SLE. These four SLE subgroups differ regarding associations with HLA‐DRB1 alleles and immunological and clinical features, suggesting dissimilar disease pathways.

The Influence of an Elastase-Sensitive Complement C5 Variant on Lupus Nephritis and Its Flare

Introduction

A C5 polymorphism (rs17611, 2404G>A) exists where the G allele associates with enhanced C5a-like production by neutrophil elastase. This cohort study investigated the influence of this polymorphism as a risk factor for lupus nephritis (LN), and on C5a and membrane attack complex (MAC) levels in LN during flare.

Methods

A cohort of lupus patients (n = 155) was genotyped for the 2404G>A polymorphism. A longitudinal LN subset (n = 66) was tested for plasma and urine levels of C5a and MAC 4 and/or 2 months before and at nonrenal or LN flare.

Results

The 2404G allele and 2404-GG genotype were associated with LN in black, but not white, lupus patients. In the longitudinal cohort, neither urine nor plasma C5a levels changed at nonrenal flare regardless of 2404G>A genotype or race. Urine (but not plasma) C5a levels increased at LN flare independent of race, more so in 2404-GG patients where 8 of 30 LN flares exhibited very high C5a levels. Higher proteinuria and serum creatinine levels also occurred in these eight flares. Urine (but not plasma) MAC levels also increased at LN flare in 2404-GG patients and correlated with urine C5a levels.

Conclusions

The C5 2404-G allele/GG genotype is a potential risk factor for LN uniquely in black lupus patients. The GG genotype is associated with sharp increases in urine C5a and MAC levels in a subset of LN flares that correspond to higher LN disease indices. The lack of corresponding changes in plasma suggests these increases reflect intrarenal complement activation.

When Distress Becomes Somatic: Dementia Family Caregivers' Distress and Genetic Vulnerability to Pain and Sleep Problems

BACKGROUND AND OBJECTIVES

Stress can trigger physical pain and disturb sleep. Whether dementia family caregivers experience heightened pain is unknown. Cycles of unwanted thoughts about caregiving stressors and avoidance of these thoughts-that is, caregiving-related distress-may exacerbate both pain and sleep disturbances, and genetic susceptibility to stress may further modulate these associations.

RESEARCH DESIGN AND METHODS

Dementia caregivers (72 spouses, 58 adult children, ages 34-89) rated the extent to which they experienced unintended thoughts about caregiving and tried to suppress such thoughts. They also reported their pain levels, sleep problems, and depressive symptoms. Peripheral blood leukocytes were genotyped for 5-HTTLPR (serotonin-transporter-linked polymorphic region) and 5-HT1A receptor polymorphism rs6295 on the 5HTR1A locus.

RESULTS

Short-allele carriers for 5-HTTLPR experienced more pain and sleep problems in association with greater caregiving-related distress than those with other genotypes. For rs6295, C carriers also showed the strongest links between distress and sleep problems. Those who experienced more avoidance and intrusive thoughts about caregiving had more severe depressive symptoms, consistent with past work.

DISCUSSION AND IMPLICATIONS

Caregivers' genetic profiles helped to explain whether caregiving-related distress predicted worse pain and sleep problems. These data reveal new somatic risks of caregiver distress and provide targets for intervention. According to plasticity theories, caregivers genetically predisposed to greater stress reactivity may also respond particularly well to interventions, and many brief treatments may effectively address caregivers' intrusions and avoidance.

The Urine Preservative Acetic Acid Degrades Urine Protein: Implications for Urine Biorepositories and the AASK Cohort Study

Patients enrolled in the African American Study of Kidney Disease and Hypertension (AASK) Cohort Study who exhibited overt proteinuria have been reported to show high nonalbumin proteinuria (NAP), which is characteristic of a tubulopathy. To determine whether African American Study of Kidney Disease and Hypertension nephropathy (AASK-N) is a tubulopathy, we obtained urine samples of 37 patients with AASK-N, with 24-hour protein-to-creatinine ratios (milligrams per milligram) ranging from 0.2 to 1.0, from the National Institute of Diabetes and Digestive Kidney Diseases repository and tested for seven markers of tubular proteinuria. By protocol, each sample had been collected in acetic acid (0.5%; mean final concentration). Compared with samples from patients with lupus nephritis or healthy black controls, AASK-N samples had lower amounts of six markers. Four markers (albumin, β-2-microglobulin, cystatin C, and osteopontin) were undetectable in most AASK-N samples. Examination by SDS-PAGE followed by protein staining revealed protein profiles indicative of severe protein degradation in 34 of 37 AASK-N urine samples. Treatment of lupus nephritis urine samples with 0.5% acetic acid produced the same protein degradation profile as that of AASK-N urine. We conclude that the increased NAP in AASK-N is an artifact of acetic acid-mediated degradation of albumin. The AASK-N repository urine samples have been compromised by the acetic acid preservative.

Biomarkers of lupus nephritis histology and flare: deciphering the relevant amidst the noise

Biomarker development in lupus nephritis (LN) has traditionally relied on comparing the characteristics of candidate markers to clinical findings in patients and controls from cross-sectional cohorts. In this work, two additional strategies for LN biomarker development that are gaining ground will be discussed. One approach compares analytes directly to kidney histology. The second strategy utilizes longitudinal measurements of biomarker levels at regular intervals as patients move from disease quiescence to disease flare. These approaches have begun to empower biomarkers as diagnostic and prognostic tools in LN and have revealed novel and sometimes unexpected roles for these biomarkers in the pathogenesis and prediction of LN disease activity.

The interleukin-6-hepcidin-hemoglobin circuit in systemic lupus erythematosus flares

Objective Hepcidin regulates iron availability and may be responsible for the anemia of chronic disease because it is induced by interleukin-6. This study investigated the IL-6-hepcidin-hemoglobin axis in patients with lupus. Methods IL-6 and hepcidin were measured in serial serum samples collected before, during and after lupus flares by specific ELISAs. Results During renal and non-renal SLE flare cycles IL-6 did not predict hepcidin and hepcidin did not predict hemoglobin. When lupus nephritis patients were in remission, IL-6 and hepcidin were correlated, but hepcidin and hemoglobin were not. Conclusion Hepcidin does not contribute significantly to anemia during active lupus.

Relationship of Circulating Anti-C3b and Anti-C1q IgG to Lupus Nephritis and Its Flare

BACKGROUND AND OBJECTIVES

Autoantibodies to complement C1q (anti-C1q) are associated with the diagnosis of lupus nephritis. In this study, we compare anti-C1q IgG with another complement autoantibody, anti-C3b IgG, as a biomarker of lupus nephritis and lupus nephritis flare.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Our investigation involved the Ohio SLE Study, a prospective observational cohort of patients with recurrently active lupus who were followed bimonthly. Serum anti-C1q and anti-C3b IgG levels were assessed cross-sectionally by ELISA in 40 normal controls and 114 patients in the Ohio SLE Study (41 nonrenal and 73 lupus nephritis) at study entry, and longitudinally in a subset of patients in the Ohio SLE Study with anti-C1q-positive lupus nephritis in samples collected every 2 months for 8 months leading up to lupus nephritis flare (n=16 patients).

RESULTS

In the cross-sectional analysis, compared with anti-C1q IgG, anti-C3b IgG was less sensitive (36% versus 63%) but more specific (98% versus 71%) for lupus nephritis. Only anti-C3b IgG was associated with patients with lupus nephritis who experienced at least one lupus nephritis flare during the Ohio SLE Study period (P<0.01). In the longitudinal analysis, circulating levels of anti-C1q IgG increased at the time of lupus nephritis flare only in patients who were anti-C3b positive (P=0.02), with significant increases occurring from 6 (38% increase) and 4 months (41% increase) before flare. Anti-C3b IgG levels also trended up at lupus nephritis flare, although the change did not reach statistical significance (P=0.07). Neither autoantibody increased 2 months before flare.

CONCLUSIONS

Although not as prevalent as anti-C1q IgG, anti-C3b IgG showed nearly complete specificity for lupus nephritis. The presence of anti-C3b IgG identified patients with lupus nephritis who were prone to flare and in whom serial measurements of markers associated with complement, such as anti-C1q IgG, may be useful to monitor lupus nephritis activity.

End-stage renal disease in African Americans with lupus nephritis is associated with APOL1

OBJECTIVE

Lupus nephritis (LN) is a severe manifestation of systemic lupus erythematosus (SLE) that exhibits familial aggregation and may progress to end-stage renal disease (ESRD). LN is more prevalent among African Americans than among European Americans. This study was undertaken to investigate the hypothesis that the apolipoprotein L1 gene (APOL1) nephropathy risk alleles G1/G2, common in African Americans and rare in European Americans, contribute to the ethnic disparity in risk.

METHODS

APOL1 G1 and G2 nephropathy alleles were genotyped in 855 African American SLE patients with LN-ESRD (cases) and 534 African American SLE patients without nephropathy (controls) and tested for association under a recessive genetic model, by logistic regression.

RESULTS

Ninety percent of the SLE patients were female. The mean ± SD age at SLE diagnosis was significantly lower in LN-ESRD cases than in SLE non-nephropathy controls (27.3 ± 10.9 years versus 39.5 ± 12.2 years). The mean ± SD time from SLE diagnosis to development of LN-ESRD in cases was 7.3 ± 7.2 years. The G1/G2 risk alleles were strongly associated with SLE-ESRD, with 25% of cases and 12% of controls having 2 nephropathy alleles (odds ratio [OR] 2.57, recessive model P = 1.49 × 10(-9)), and after adjustment for age, sex, and ancestry admixture (OR 2.72, P = 6.23 × 10(-6)). The age-, sex-, and admixture-adjusted population attributable risk for ESRD among patients with G1/G2 polymorphisms was 0.26, compared to 0.003 among European American patients. The mean time from SLE diagnosis to ESRD development was ∼2 years earlier among individuals with APOL1 risk genotypes (P = 0.01).

CONCLUSION

APOL1 G1/G2 alleles strongly impact the risk of LN-ESRD in African Americans, as well as the time to progression to ESRD. The high frequency of these alleles in African Americans with near absence in European Americans explains an important proportion of the increased risk of LN-ESRD in African Americans.

High-sensitivity C-reactive protein, disease activity, and cardiovascular risk factors in systemic lupus erythematosus

OBJECTIVE

To study the level of high-sensitivity C-reactive protein (hsCRP) and its relationship with disease activity, damage, and cardiovascular risk factors in patients with systemic lupus erythematosus (SLE).

METHODS

Consecutive patients who fulfilled ≥4 American College of Rheumatology criteria for SLE who did not have a concurrent infection were recruited. Blood was assayed for hsCRP level, and disease activity, organ damage of SLE, and cardiovascular risk factors were assessed. Linear regression analyses were performed for the relationship between hsCRP levels, SLE activity, damage, and cardiovascular risk factors.

RESULTS

In total, 289 patients were studied (94% women, mean ± SD age 39.0 ± 13.1 years, and mean ± SD SLE duration 7.8 ± 6.7 years). The mean ± SD Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) score was 4.9 ± 5.6 and clinically active SLE was present in 122 patients (42%). The mean ± SD hsCRP level was 4.87 ± 12.7 mg/liter, and 28 patients with active SLE (23%) had an undetectable hsCRP level (<0.3 mg/liter). The linear regression analyses revealed a significant correlation between hsCRP level and musculoskeletal disease (β = 0.21), hematologic disease (β = 0.19), active serositis (β = 0.46), and clinical SLEDAI score (β = 0.24) after adjusting for age, sex, body mass index, serum creatinine, and the use of various medications (P < 0.005 for all). hsCRP levels correlated significantly with anti-double-stranded DNA titer (β = 0.33, P < 0.001) but did not correlate with complement C3 (β = -0.07, P = 0.26). An hsCRP level >3 mg/liter was significantly associated with male sex, long-term smoking, diabetes mellitus, a higher atherogenic index, and a history of arterial thrombosis. hsCRP levels correlated significantly with pulmonary and endocrine damage scores.

CONCLUSION

hsCRP was detectable in 77% of SLE patients with clinically active disease and correlated with SLEDAI scores, particularly in serositis and in the musculoskeletal and hematologic systems. Elevated hsCRP levels in SLE were associated with certain cardiovascular risk factors and a history of arterial thromboembolism.

Novel estrogen target gene ZAS3 is overexpressed in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a prototypic, inflammatory autoimmune disease characterized by significant gender bias. Previous studies have established a role for hormones in SLE pathogenesis, including the sex hormone estrogen. Estrogen regulates gene expression by translocating estrogen receptors (ER) α and β into the nucleus where they induce transcription by binding to estrogen response elements (EREs) of target genes. The ZAS3 locus encodes a signaling and transcriptional molecule involved in regulating inflammatory responses. We show that ZAS3 is significantly up-regulated in SLE patients at both the protein and mRNA levels in peripheral blood mononuclear cells (PBMCs). Furthermore, estrogen stimulates the expression of ZAS3 in vitro in several leukocyte and breast cancer cell lines of both human and murine origin. In vivo estrogen treatment mediates induction of tissue specific ZAS3 expression in several lymphoid organs in mice. Estrogen stimulation also significantly up-regulates ZAS3 expression in primary PBMCs, while treatment with testosterone has no effect. Mechanistically, estrogen induces differential ERα binding to putative EREs within the ZAS3 gene and ERα knockdown with siRNA prevents estrogen induced ZAS3 up-regulation. In contrast, siRNA targeting IFNα has no effect. These data demonstrate that ZAS3 expression is directly regulated by estrogen and that ZAS3 is overexpressed in lupus. Since ZAS3 has been shown to regulate inflammatory pathways, its up-regulation by estrogen could play a critical role in female-biased autoimmune disorders.

FcγRIIb on liver sinusoidal endothelium clears small immune complexes

It has long been known that the ITIM-bearing IgG Fc receptor (FcγRIIb, RIIb) is expressed on liver sinusoidal endothelial cells (LSEC) and that the liver is the major site of small immune complex (SIC) clearance. Thus, we proposed that RIIb of LSEC eliminates blood-borne SIC, thereby controlling immune complex-mediated autoimmune disease. Testing this hypothesis, we found most RIIb of the mouse, fully three-quarters, to be expressed in liver. Moreover, most (90%) liver RIIb was expressed in LSEC, the remainder in Kupffer cells. An absent FcRγ in LSEC implied that RIIb is the sole FcγR expressed. Testing the capacity of liver RIIb to clear blood-borne SIC, we infused mice intravenously with radio-iodinated SIC made of OVA and rabbit IgG anti-OVA. Tracking decay of SIC from the blood, we found the RIIb knockout strain to be severely deficient in eliminating SIC compared with the wild-type strain, terminal half-lives being 6 and 1.5 h, respectively. RIIb on LSEC, a major scavenger, keeps SIC blood concentrations low and minimizes pathologic deposition of inflammatory immune complex.

Evidence that abnormally large seasonal declines in vitamin D status may trigger SLE flare in non-African Americans

Cross-sectional studies have shown that low vitamin D (25-hydroxyvitamin D (25(OH)D)) is associated with increased systemic lupus erythematosus (SLE) activity. This study is the first to assess the temporal relationship between 25(OH)D levels and onset of SLE flare. This assessment was made possible because of the specimen bank and database of the Ohio SLE Study (OSS), a longitudinal study of frequently relapsing SLE that involved regular bimonthly patient follow-up. We identified for this study 82 flares from 46 patients that were separated by at least 8 months from previous flares. Serum 25(OH)D levels were measured at 4 and 2 months before flare, and at the time of flare (a flare interval). We found that for flares occurring during low daylight months (LDM, Oct-Mar), 25(OH)D levels were decreased at the time of flare, but only in non-African American (non-AA) patients (32% decrease at flare, compared to 4 months prior, p < 0.001). To control for seasonal effects, we also measured 25(OH)D levels in the LDM "no-flare" intervals, which were intervals that matched to the same calendar months of the patients' LDM flare intervals, but that didn't end in flare (n = 24). For these matches, a significant decrease occurred in 25(OH)D levels during the flare intervals (18.1% decrease, p < 0.001), but not during the matching no-flare intervals (6.2% decrease, p = 0.411). For flares occurring during high daylight months (HDM), 25(OH)D levels changed only in non-AA patients, increasing slightly (5.6%, p = 0.010). Analysis of flare rates for the entire OSS cohort (n = 201 flares) revealed a tendency for higher flare rates during LDM compared to HDM, but again only in non-AA patients (p = 0.060). Flare rates were lower during HDM for non-AA patients compared to AA patients (p = 0.028). In conclusion, in non-AA SLE patients, unusually large declines in 25(OH)D during LDM may be mechanistically related to SLE flare, whereas relatively high 25(OH)D levels during HDM may protect against flare.

Characterization of glomerular diseases using proteomic analysis of laser capture microdissected glomeruli

The application of molecular techniques to characterize clinical kidney biopsies has the potential to provide insights into glomerular diseases that cannot be revealed by traditional renal pathology. The present work is a proof-of-concept approach to test whether proteomic analysis of glomeruli isolated from clinical biopsies by laser capture microdissection can provide unique information regarding differentially expressed proteins relevant to disease pathogenesis. The proteomes of glomeruli isolated by laser capture microdissection from biopsies of normal kidneys (living-related donor kidneys) were compared with those from patients with diabetic nephropathy, lupus nephritis, and fibronectin glomerulopathy. Glomerular proteins were extracted, trypsin digested, and subjected to liquid chromatography-tandem mass spectrometry for identification and quantitation. Relative to normal glomeruli, all disease-associated glomeruli showed an increased presence of complement components, a marked decline in podocyte-associated proteins, and a decrease in proteins associated with cellular metabolism. Additionally, fibronectin glomerulopathy glomeruli differed from all the other glomeruli because of a significant accumulation of fibronectin and fibulin. This study demonstrates that our method acquires reproducible and quantitative proteomic information from laser capture microdissection isolates that can be used to characterize the molecular features of glomerular diseases.

Vitamin D deficiency as marker for disease activity and damage in systemic lupus erythematosus: a comparison with anti-dsDNA and anti-C1q

Objectives: To study the sensitivity and specificity of vitamin D deficiency for predicting disease activity and damage of systemic lupus erythematosus (SLE) in comparison with anti-dsDNA and anti-C1q. Methods: Consecutive patients who fulfilled four or more ACR criteria for SLE were studied. Levels of 25-hydroxyvitamin D3, anti-C1q, anti-dsDNA and complement levels were measured. Relationship among these markers, concurrent disease activity and damage scores of SLE was studied by Spearman's rank correlation method. Results: In total, 290 SLE patients were studied (95% women; mean age 38.9 ± 13.1 years; SLE duration 7.7 ± 6.7 years). Clinical or serological lupus activity (SLEDAI ≥ 1) was present in 225 (78%) patients. Vitamin D deficiency (< 15 ng/ml) was detected in 78 (27%) patients. Levels of 25-hydroxyvitamin D3 correlated inversely with the clinical SLE disease activity score (Rho = −0.26; p < 0.001). A negative correlation was also observed between 25-hydroxyvitamin D3 and anti-dsDNA levels (Rho = −0.13; p = 0.02), or anti-C1q (Rho = −0.14; p = 0.02). However, there was no significant relationship between levels of 25-hydroxyvitamin D3 and complement C3 (Rho = 0.09; p = 0.12) or C4 (Rho = 0.09; p = 0.13). Both 25-hydroxyvitamin D3 deficiency and anti-C1q were more specific but less sensitive than anti-dsDNA for concurrent clinical renal and non-renal SLE activity. Levels of 25-hydroxyvitamin D3, anti-dsDNA or anti-C1q did not correlate significantly with the SLE damage scores. Conclusions: 25-hydroxyvitamin D3 correlated inversely and significantly with clinical SLE activity, anti-C1q and anti-dsDNA titers, but not with complement levels or damage scores. Deficiency of 25-hydroxyvitamin D3 was as specific as anti-C1q, but less sensitive than anti-dsDNA, for detecting concurrent renal and non-renal clinical activity of SLE.

An approach to validating criteria for proteinuric flare in systemic lupus erythematosus glomerulonephritis

OBJECTIVE

Published criteria on the degree of proteinuria increase that defines a proteinuric flare in systemic lupus erythematosus (SLE) with glomerulonephritis (GN) vary widely, likely because they are not evidence based, but are largely based on expert opinion. Ideally, the threshold for proteinuric flare should be set sufficiently high that spontaneous variation in proteinuria does not likely explain the increase, but not so high that the patient needlessly experiences prolonged severe proteinuria before a flare is declared and therapy is increased. The present study was undertaken to develop an evidence-based approach to setting the threshold for proteinuric flare, based on quantifying the spontaneous variation in the urine protein:creatinine ratio in SLE GN patients who are not experiencing SLE flare.

METHODS

SLE GN patients (n = 71) in the Ohio SLE Study were tested at prespecified bimonthly intervals within windows of ±1 week. The median duration of followup was >44 months, and the rate of visit compliance was >90%. To assess spontaneous variation in the protein:creatinine ratio under no-flare conditions, we excluded protein:creatinine ratios measured within 4 months before or after renal flare.

RESULTS

Our findings showed that in the group of SLE GN patients with a mean no-flare protein:creatinine ratio of ≤0.5, the published flare thresholds are set well above the 99% confidence interval of the no-flare protein:creatinine ratio. The opposite was seen in the group with a mean no-flare protein:creatinine ratio of ≥1.0.

CONCLUSION

Current thresholds for defining proteinuric flare appear to be set either too high or too low. A randomized trial would be needed to test whether resetting the thresholds would result in faster remission, reduction in therapy, and decrease in the frequency of chronic kidney disease.

Vitamin D levels in Chinese patients with systemic lupus erythematosus: relationship with disease activity, vascular risk factors and atherosclerosis

OBJECTIVES

To study the relationship of 25(OH)D(3) level with disease activity, vascular risk factors and atherosclerosis in SLE.

METHODS

Consecutive patients who fulfilled four or more ACR criteria for SLE were recruited for assay of 25(OH)D(3) level. Disease activity was assessed by the SLEDAI and physicians' global assessment (PGA). Patients with vascular risk factors were screened for atherosclerosis at the coronary or carotid arteries. Correlation between 25(OH)D(3) levels and SLEDAI scores was studied by linear regression. The link between vascular risk factors, atherosclerosis and vitamin D deficiency was also examined.

RESULTS

A total of 290 SLE patients were studied [94% women; mean (s.d.) age 38.9 (13.1) years; disease duration 7.7 (6.7) years; 78% patients had clinical or serological lupus activity]. Two hundred and seventy-seven (96%) patients had vitamin D insufficiency [25(OH)D(3) < 30 ng/ml] and 77 (27%) patients had vitamin D deficiency (<15 ng/ml). Levels of 25(OH)D(3) correlated inversely with PGA (β -0.20; P = 0.003), total SLEDAI scores (β -0.19; P = 0.003) and subscores due to active renal, musculoskeletal and haematological disease. Subjects with vitamin D deficiency had significantly higher total/high-density lipoprotein (HDL) cholesterol ratio [3.96 (2.94) vs 3.07 (0.80); P = 0.02] and prevalence of aPLs (57 vs 39%; P = 0.007). Of 132 patients, 58 (44%) with vascular risk factors screened were positive for subclinical atherosclerosis. No association could be demonstrated between 25(OH)D(3) level and atherosclerosis, which was mainly associated with increasing age, menopause, obesity and hyper-triglyceridaemia.

CONCLUSIONS

In this large cross-sectional study of SLE patients, 25(OH)D(3) level correlates inversely with disease activity. Vitamin D deficiency is associated with dyslipidaemia. In patients with vascular risk factors, subclinical atherosclerosis is not associated with hypovitaminosis D.

The complex nature of serum C3 and C4 as biomarkers of lupus renal flare

To assess the relationship between serum C3 or C4 levels and lupus renal flare, C3 and C4 levels were measured bimonthly in 71 lupus nephritis patients for a mean of 35 months, during which time 70 renal flares were identified. Comparing baseline, pre-flare, and at-flare values indicated that neither C3 nor C4 levels decreased pre-flare, but both decreased on average significantly at flare. However, sensitivity/specificity for C3 (75%/71%) and C4 (48%/71%) were low. To account for other influencing factors, multiple regression was performed that included bimonthly values of C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), and genotype data on C3 (S/F), CRP (1846G > A), and the complement regulator factor H (Y402H). This analysis revealed that reduced levels of C4, but not C3, were independently associated with the two-month pre-flare period. Conversely, reduced levels of C3, but not C4, were independently associated with the flare visit. Significant pro-flare interactions included low C3 levels with the factor H 402HH-encoding genotype, and low CRP levels with the C3 F allele. Together these data suggest that C4 activation is critical for initiating renal flare while C3 activation is involved in the actual tissue damage, and that these effects are influenced by genetic variability in complement activation and regulation.

Mathematical framework for human SLE Nephritis: disease dynamics and urine biomarkers

BACKGROUND

Although the prognosis for Lupus Nephritis (LN) has dramatically improved with aggressive immunosuppressive therapies, these drugs carry significant side effects. To improve the effectiveness of these drugs, biomarkers of renal flare cycle could be used to detect the onset, severity, and responsiveness of kidney relapses, and to modify therapy accordingly. However, LN is a complex disease and individual biomarkers have so far not been sufficient to accurately describe disease activity. It has been postulated that biomarkers would be more informative if integrated into a pathogenic-based model of LN.

RESULTS

This work is a first attempt to integrate human LN biomarkers data into a model of kidney inflammation. Our approach is based on a system of differential equations that capture, in a simplified way, the complexity of interactions underlying disease activity. Using this model, we have been able to fit clinical urine biomarkers data from individual patients and estimate patient-specific parameters to reproduce disease dynamics, and to better understand disease mechanisms. Furthermore, our simulations suggest that the model can be used to evaluate therapeutic strategies for individual patients, or a group of patients that share similar data patterns.

CONCLUSIONS

We show that effective combination of clinical data and physiologically based mathematical modeling may provide a basis for more comprehensive modeling and improved clinical care for LN patients.

Can we personalize treatment for kidney diseases?

The idea of individualizing therapies to obtain optimal clinical results is not new but has only recently been applied to kidney diseases. Nonetheless, kidney disorders present a variety of opportunities to personalize medicine. Here, the heterogeneity of kidney disorders is reviewed to provide a rationale for pursuing personalized medicine. Data on adjusting therapy on the basis of pharmacogenetics/genomics and pharmacodynamics are summarized to demonstrate where the field is, and biomarker studies that reflect the future of personalized medicine are discussed. The goal of this review is to demonstrate that we can personalize therapy for kidney diseases but that considerable investment in new research will be required for personalized medicine to be routinely used in nephrology clinics.

Random spot urine protein/creatinine ratio is unreliable for estimating 24-hour proteinuria in individual systemic lupus erythematosus nephritis patients

BACKGROUND

Recently the American Rheumatologic Association (ARA) recommended random spot urine protein/creatinine ratio (P/C) to monitor systemic lupus erythematosus (SLE) glomerulonephritis (GN). Shortly afterward, 2 works were published, designated Study 1 and Study 2, which are the only studies to test spot P/C in SLE GN. Here we evaluate Study 1 and Study 2, which came to different conclusions.

METHODS

Study 1 compared spot P/C to the P/C of intended 24-hour collections >50% complete, which reliably estimates 24-hour proteinuria. Study 2 compared spot P/C to the protein content of intended 24-hour collections >80% complete. To compare studies, Study 2 data were converted to P/C ratios.

RESULTS

Study 1 and Study 2 were found to be in agreement. Both showed that spot P/C and 24-hour P/C were highly correlated, but only when compared over the entire P/C range (0-8.0) (r = 0.842). Over the P/C range 0.5-3.0 (the most common P/C range encountered in SLE GN), correlation was present, but concordance was poor, rendering random P/C ratio unreliable.

CONCLUSIONS

Random spot P/C ratio is unreliable for detecting moderate proteinuria change. For example, random spot P/C would not reliably diagnose British Isles Lupus Assessment Group (BILAG) Category A or B proteinuric flares.

D-dimer level and the risk for thrombosis in systemic lupus erythematosus

BACKGROUND AND OBJECTIVES

Patients who have systemic lupus erythematosus (SLE) and manifest antiphospholipid antibodies (APA) are at increased risk for thrombosis; however, it is difficult to predict who will clot. This study tested the hypothesis that peak D-dimer level measured routinely during follow-up identifies whether a hypercoagulable state is developing and, therefore, the patient is at increased risk for thrombosis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

One hundred consecutive patients who had SLE with recurrent activity (71% renal SLE) and were evaluated for or enrolled in the Ohio SLE Study were studied. D-dimer testing was done annually and usually at SLE flare or other serious illness. When D-dimer was elevated, evaluation for thrombosis (large vessel, small vessel, or Libman-Sacks) was undertaken. Mean follow-up was 37.5 +/- 15 SD months.

RESULTS

Of those with peak D-dimer <0.5 microg/ml (n = 46), 0% thrombosed, 33% had APA. Of those with peak D-dimer 0.5 to 2.0 microg/ml (n = 19), 6% thrombosed, 44% had APA. Of those with peak D-dimer >2.0 microg/ml (n = 36), 42% thrombosed, 76% had APA. The most common causes of elevated D-dimer in the absence of demonstrable thrombosis were SLE flare and systemic infection. D-dimer levels were usually elevated for several months before thrombosis.

CONCLUSIONS

Patients with SLE and normal D-dimer levels are at low risk for thrombosis, irrespective of APA status. Those with persistent unexplained elevated D-dimer levels, particularly when >2.0 microg/ml, are at high risk for thrombosis.

Biomarkers of lupus nephritis determined by serial urine proteomics

Lupus nephritis is a frequent and serious complication of systemic lupus erythematosus (SLE), the treatment of which often requires the use of immunosuppressives that can have severe side effects. Here we determined the low-molecular weight proteome of serial lupus urine samples to uncover novel and predictive biomarkers of SLE renal flare. Urine from 25 flare cycles of 19 patients with WHO Class III, IV, and V SLE nephritis were obtained at baseline, pre-flare, flare and post-flare. Each sample was first fractionated to remove proteins larger than 30 kDa, then applied onto weak cation exchanger protein chips for analysis by SELDI-TOF mass spectrometry. We found 176 protein ions of which 27 were differentially expressed between specific flare intervals. On-chip peptide sequencing by integrated tandem mass spectrometry positively identified the 20 and 25 amino-acid isoforms of hepcidin, as well as fragments of alpha1-antitrypsin and albumin among the selected differentially expressed protein ions. Hepcidin 20 increased 4 months before renal flare and returned to baseline at renal flare, whereas hepcidin 25 decreased at renal flare and returned to baseline 4 months after the flare. These studies provide a beginning proteomic analysis aimed at predicting impending renal relapse, relapse severity, and the potential for recovery after SLE nephritis flare.

Relationship between albuminuria and total proteinuria in systemic lupus erythematosus nephritis: diagnostic and therapeutic implications

BACKGROUND AND OBJECTIVES

Albuminuria is regarded a sensitive measure of progression of glomerular disease. This study was undertaken in patients who had systemic lupus erythematosus glomerulonephritis (n = 57) and were followed in the Ohio SLE Study to determine whether measuring albuminuria offered clinical advantages over that of total proteinuria.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Twenty-four-hour urine collections (n = 127) were obtained at baseline and annually for measurement of microalbumin, total protein, and creatinine.

RESULTS

There was a strong linear relationship between microalbumin-creatinine and protein-creatinine ratios over the entire range of protein-creatinine ratios; however, in the protein-creatinine ratio range 0.0 to 0.3, as the protein-creatinine ratio increased, the microalbumin-protein ratio increased much more than the protein-creatinine ratio. Also, the greater the protein-creatinine ratio, the greater was the evidence for nonselective proteinuria (protein-creatinine ratio--microalbumin-creatinine ratio).

CONCLUSIONS

For the diagnosis of proteinuria renal flare, measuring albuminuria offers no advantage over measuring total proteinuria because changes in protein-creatinine and microalbumin-creatinine ratios are highly correlated over the designated ranges for systemic lupus erythematosus glomerulonephritis proteinuric flares. In those with normal-range proteinuria, subsequent changes in microalbumin-protein ratio might be a better forecaster of renal flare than changes in protein-creatinine or microalbumin-creatinine ratio. High protein-creatinine ratios are associated with evidence of nonselective proteinuria, which may increase the nephrotoxicity of proteinuria. Thus, using high-threshold criteria for systemic lupus erythematosus flare (allowing greater proteinuria increase before flare is declared) may expose the kidney to greater nephrotoxicity than using the low-threshold criteria for systemic lupus erythematosus flare.

Sensitive and specific real-time polymerase chain reaction assays to accurately determine copy number variations (CNVs) of human complement C4A, C4B, C4-long, C4-short, and RCCX modules: elucidation of C4 CNVs in 50 consanguineous subjects with defined HLA genotypes

Recent comparative genome hybridization studies revealed that hundreds to thousands of human genomic loci can have interindividual copy number variations (CNVs). One of such CNV loci in the HLA codes for the immune effector protein complement component C4. Sensitive, specific, and accurate assays to interrogate the C4 CNV and its associated polymorphisms by using submicrogram quantities of genomic DNA are needed for high throughput epidemiologic studies of C4 CNVs in autoimmune, infectious, and neurological diseases. Quantitative real-time PCR (qPCR) assays were developed using TaqMan chemistry and based on sequences specific for C4A and C4B genes, structural characteristics corresponding to the long and short forms of C4 genes, and the breakpoint region of RP-C4-CYP21-TNX (RCCX) modular duplication. Assignments for gene copy numbers were achieved by relative standard curve methods using cloned C4 genomic DNA covering 6 logs of DNA concentrations for calibrations. The accuracies of test results were cross-confirmed internally in each sample, as the sum of C4A plus C4B equals to the sum of C4L plus C4S or the total copy number of RCCX modules. These qPCR assays were applied to determine C4 CNVs from samples of 50 consanguineous subjects who were mostly homozygous in HLA genotypes. The results revealed eight HLA haplotypes with single C4 genes in monomodular RCCX that are associated with multiple autoimmune and infectious diseases and 32 bimodular, 4 trimodular, and one quadrimodular RCCX. These C4 qPCR assays are proven to be robust, sensitive, and reliable, as they have contributed to the elucidation of C4 CNVs in >1000 human samples with autoimmune and neurological diseases.

Spot urine protein/creatinine ratios are unreliable estimates of 24 h proteinuria in most systemic lupus erythematosus nephritis flares

The diagnosis of glomerulonephritis flares in systemic lupus erythematosus (SLE) is usually based on whether the magnitude of proteinuria has changed. Our study tests two methods to assess proteinuric change: protein/creatinine (P/C) ratios of intended 24-h urine collections or that of spot urine samples. Sixty-four patients with glomerulonephritis due to SLE followed in the Ohio SLE Study provided bimonthly paired spot and intended 24-h urine collections. Completeness of each collection was estimated as the ratio of the measured creatinine to the expected creatinine based upon Cockroft-Gault. Intended 24-h urine collections with measured/expected creatinine ratios between 0.5 and 0.9 (237 samples overall) showed ratios that were not significantly different from ratios of complete 24-h urine collections with ratios of 0.9-1.1 (159 samples). To compare spot and 24 h P/C ratios, we randomly selected pairs of samples with measured/expected ratios above 0.75. Consistent with previous studies, spot and 24-h urine P/C ratios showed good correlation over the range of values as well as reasonably strong concordance. Over the range of most SLE glomerulonephritis flares, however, correlation was present but concordance was poor. Our work suggests that the use of spot urine P/C ratios will yield more false-positive and -negative diagnoses of glomerulonephritis flares in patients with SLE than the ratio in 24-h urines.

Gene copy-number variation and associated polymorphisms of complement component C4 in human systemic lupus erythematosus (SLE): low copy number is a risk factor for and high copy number is a protective factor against SLE susceptibility in European Americans

Interindividual gene copy-number variation (CNV) of complement component C4 and its associated polymorphisms in gene size (long and short) and protein isotypes (C4A and C4B) probably lead to different susceptibilities to autoimmune disease. We investigated the C4 gene CNV in 1,241 European Americans, including patients with systemic lupus erythematosus (SLE), their first-degree relatives, and unrelated healthy subjects, by definitive genotyping and phenotyping techniques. The gene copy number (GCN) varied from 2 to 6 for total C4, from 0 to 5 for C4A, and from 0 to 4 for C4B. Four copies of total C4, two copies of C4A, and two copies of C4B were the most common GCN counts, but each constituted only between one-half and three-quarters of the study populations. Long C4 genes were strongly correlated with C4A (R=0.695; P<.0001). Short C4 genes were correlated with C4B (R=0.437; P<.0001). In comparison with healthy subjects, patients with SLE clearly had the GCN of total C4 and C4A shifting to the lower side. The risk of SLE disease susceptibility significantly increased among subjects with only two copies of total C4 (patients 9.3%; unrelated controls 1.5%; odds ratio [OR] = 6.514; P=.00002) but decreased in those with > or =5 copies of C4 (patients 5.79%; controls 12%; OR=0.466; P=.016). Both zero copies (OR=5.267; P=.001) and one copy (OR=1.613; P=.022) of C4A were risk factors for SLE, whereas > or =3 copies of C4A appeared to be protective (OR=0.574; P=.012). Family-based association tests suggested that a specific haplotype with a single short C4B in tight linkage disequilibrium with the -308A allele of TNFA was more likely to be transmitted to patients with SLE. This work demonstrates how gene CNV and its related polymorphisms are associated with the susceptibility to a human complex disease.

Biomarker discovery in human SLE nephritis

The treatment of systemic lupus erythematosus (SLE) nephritis, while effective, is associated with significant morbidity and mortality. These side effects could be mitigated if the onset, severity, and response of renal flare could be predicted, and therapy modified accordingly. In this review, an approach to derive prediction equations of SLE nephritis flare is discussed. Integral to generating such prediction equations is the identification of biomarkers of lupus nephritis that can serve as input variables for modeling flare. The use of urine as a source of SLE nephritis biomarkers is described, and the results of urine biomarker discovery studies using candidate and proteomic approaches are presented.

Fluctuation in self-perceived stress and increased risk of flare in patients with lupus nephritis carrying the serotonin receptor 1A -1019 G allele

OBJECTIVE

Stress is believed to be a risk factor for systemic lupus erythematosus (SLE) flare. Two serotonin-related gene polymorphisms, the serotonin receptor 1A (5-HT1A) polymorphism at -1019C>G and the serotonin transporter LS polymorphism, have been reported to affect stress-related behaviors. The purpose of this study was to assess the relationship between self-perceived stress (SPS), variability in SPS, and the 2 serotonin-related gene polymorphisms as risk factors for SLE flare.

METHODS

Seventy-seven SLE patients (50 with lupus nephritis) were evaluated every 2 months (mean +/- SD total followup 18.5 +/- 8.5 months), and patients recorded their daily SPS levels (0-10 scale). Values for mean SPS and coefficient of variation (CV) for SPS were calculated from the 60-day block of daily measurements between study visits. Serotonin-related gene polymorphism genotypes were determined by polymerase chain reaction-based methods.

RESULTS

Of the 77 patients, 53 experienced 80 flares of SLE (32 renal flares) based on prespecified criteria. Multivariate analysis revealed that whereas neither the serotonin-related gene polymorphisms nor the mean SPS was predictive of an SLE flare, an increased CV for SPS was predictive (P = 0.0031). Interaction between the CV for SPS and the 5-HT1A -1019C>G polymorphism was also found to be a predictor of SLE flare (P = 0.0039). Subset analysis revealed that only in lupus nephritis patients were increasing CVs for SPS (P = 0.0002) and the interaction between CVs for SPS and 5-HT1A (P < 0.0001) predictive of a flare. Odds ratio curves demonstrated that the predictive effect of increasing CVs for SPS required the presence of the 5-HT1A -1019 G allele, but appeared to be independent of the G allele number.

CONCLUSION

Fluctuation in the level of SPS is a risk factor for the onset of flare in SLE patients with major renal manifestations when it occurs on the background of a stress-related susceptibility gene (the 5-HT1A -1019 G allele).

Consumption of erythrocyte CR1 (CD35) is associated with protection against systemic lupus erythematosus renal flare

Erythrocyte complement receptor type one (E-CR1) is thought to protect against immune complex (IC) disease through interactions that lead to E-CR1 consumption, and low E-CR1 levels are characteristic of systemic lupus erythematosus (SLE). The purpose of this study was to test the hypothesis that E-CR1 consumption can predict or mark SLE flare. Recurrently active SLE patients [n = 43; 28 with past or present major renal manifestations (SLER) and 15 without (SLENR)], were evaluated every 2 months by detailed protocol testing (mean follow-up 22 months), including direct measurements of E-CR1 levels using a radioimmunoassay. In all patients, detectable E-CR1 levels fluctuated widely through acute periods of consumption and regeneration, preventing the use of any single value as a baseline. However, when individual chronic baseline values were used, determined as the mean of all E-CR1 values 4 months or more from a flare, a clear trend was observed. In 16 of 16 instances of non-renal flare in SLER patients, E-CR1 levels decreased at flare (mean decrease 34%, P < 0.0001). In contrast, no consistent difference was observed for flare in SLENR patients or for renal flare in SLER patients. Changes in E-CR1 levels did not correlate with plasma CR1 levels. In conclusion, single occurrences of E-CR1 consumption did not generally predict or mark SLE flare. However, compared to the average E-CR1 levels measured during no-flare intervals, E-CR1 consumption in SLER patients at flare was strongly associated with freedom from signs of renal involvement. We postulate that E-CR1 consumption reflects E-CR1 function that includes protecting against SLE nephritis.

Plasma, urine, and renal expression of adiponectin in human systemic lupus erythematosus

BACKGROUND

Adiponectin is an adipocyte-derived cytokine that has anti-inflammatory properties. A preliminary proteomic evaluation of urine for biomarkers of systemic lupus erythematosus (SLE) nephritis demonstrated high levels of adiponectin in SLE urine. This prompted investigation of adiponectin expression in human SLE.

METHODS

Adiponectin was measured by enzyme-linked immunosorbent assay (ELISA) in the urine and plasma of a clinically well-characterized SLE cohort, with renal and nonrenal SLE being followed in a prospective longitudinal study to identify risk factors for SLE flare. Renal adiponectin expression was assessed by immunohistochemical analysis of kidney biopsies from SLE nephritis patients.

RESULTS

Cross-sectional testing showed that plasma adiponectin levels were higher in patients with renal SLE flare than normal controls or patients with nonrenal SLE flare, after accounting for race and body mass index. Urine adiponectin levels increased significantly with renal flare, but not nonrenal SLE flare. Longitudinal testing revealed that the urine adiponectin increase began in the 2 months prior to renal flare. Urine adiponectin correlated with plasma levels and magnitude of proteinuria, and to a lesser extent serum creatinine. Plasma adiponectin levels were independent of renal function and proteinuria. In kidney biopsies, adiponectin was found on endothelial surfaces in normal and SLE kidneys, and on podocytes and in the tubules of SLE kidneys.

CONCLUSION

Plasma adiponectin levels are increased in patients with renal SLE compared to healthy controls and patients with nonrenal SLE. During renal but not nonrenal SLE flare, urine adiponectin levels increase significantly. Urine adiponectin may be a biomarker of renal SLE flare.

Patient education and access of ESRD patients to renal replacement therapies beyond in-center hemodialysis

BACKGROUND

Nephrologists report that patients' choice should play an important role in the selection of renal replacement therapy (RRT) for end-stage renal disease (ESRD). In the United States, kidney transplant rates remain low and <10% of patients utilize home dialysis therapies. This study examined the effect of pre-ESRD processes on the selection of RRT among incident ESRD patients.

METHODS

Using surveys, data were collected for all patients admitted to 229 dialysis units in ESRD Network 18 between April 1, 2002 and May 31, 2002. A total of 1365 patients began chronic dialysis and 1193 facility (87%) and 428 patient (31%) surveys were returned.

RESULTS

Substantial proportions of patients were unaware of their kidney disease (36%) or were not seeing a nephrologist (36%) until <4 months before first dialysis. The presentation of treatment options was delayed (48% either after or < 1 month before the first dialysis). The majority of ESRD patients were not presented with chronic peritoneal dialysis, home hemodialysis, or renal transplantation as options (66%, 88%, and 74%, respectively). Using multivariate analyses, variables significantly associated with selection of chronic peritoneal dialysis as dialysis modality were the probability of chronic peritoneal dialysis being presented as a treatment option and the time spent on patient education.

CONCLUSION

An incomplete presentation of treatment options is an important reason for under-utilization of home dialysis therapies and probably delays access to transplantation. Improvements in and reimbursement for pre-ESRD education could provide an equal and timely access for all medically suitable patients to various RRTs.

Identification of the Kna/Knb polymorphism and a method for Knops genotyping

BACKGROUND

DNA mutations resulting in the McCoy and Swain-Langley polymorphisms have been identified on complement receptor 1 (CR1)-a ligand for rosetting of Plasmodium falciparum-infected RBCs. The molecular identification of the Kna/Knb polymorphism was sought to develop a genotyping method for use in the study of the Knops blood group and malaria.

STUDY DESIGN AND METHODS

CR1 deletion constructs were used in inhibition studies of anti-Kna. PCR amplification of Exon 29 was followed by DNA sequencing. A PCR-RFLP was developed with NdeI, BsmI, and MfeI for the detection of Kna/Knb, McCa/McCb, and Sl1/Sl2, respectively. Knops phenotypes were determined with standard serologic techniques.

RESULTS

A total of 310 Malian persons were phenotyped for Kna with 200 (64%) Kn(a+) and 110 (36%) Kn(a-). Many of the Kn(a-) exhibited the Knops-null phenotype, that is, Helgeson. The Kna/b DNA polymorphism was identified as a V1561M mutation with allele frequencies of Kna (V1561) 0.9 and Knb (M1561) 0.1.

CONCLUSION

The high frequency (18%) of Knb in West African persons suggests that it is not solely a Caucasian trait. Furthermore, because of the high incidence of heterozygosity as well as amorphs, accurate Knops typing of donors of African descent is best accomplished by a combination of molecular and serologic techniques.

The intricate role of complement component C4 in human systemic lupus erythematosus

It was observed about 50 years ago that low serum complement activity or low protein concentrations of complement C4 concurred with disease activities of systemic lupus erythematosus (SLE). Complete deficiencies of complement components C4A and C4B, albeit rare in human populations, are among the strongest genetic risk factors for SLE or lupus-like disease, across HLA haplotypes and racial backgrounds. However, whether heterozygous or partial deficiency of C4A (C4AQ0) or C4B (C4BQ0) is a predisposing factor for SLE has been a highly controversial topic. In this review we critically analyzed past epidemiologic studies on deficiency of C4A or C4B in human SLE. Cumulative results from more than 35 different studies revealed that heterozygous and homozygous deficiencies of C4A were present in 40-60% of SLE patients from almost all ethnic groups or races investigated, which included northern and central Europeans, Anglo-Saxons, Caucasians in the US, African Americans, Asian Chinese, Koreans and Japanese. In addition, French SLE and control populations had relatively low frequencies of C4AQ0, but the difference between the patient and control groups was statistically significant. The relative risk of C4AQ0 in SLE varied between 2.3 and 5.3 among different ethnic groups. In Caucasian and African SLE patients, the two major causes for C4AQ0 are (1) the presence of a mono-S RCCX (RP-C4-CYP21-TNX) module with a single, short C4B gene in the major histocompatibility complex; and (2) a 2-bp insertion into the sequence for codon 1213 at exon 29 of the mutant C4A gene. Both mono-S structures and 2-bp insertion in exon 29 are absent or extremely rare in the C4AQ0 of Oriental SLE patients. The highly significant association of C4AQ0 with SLE across multiple HLA haplotypes and ethnic groups, and the presence of different mechanisms leading to a C4A protein deficiency among SLE patients suggested that deficiency or low expression level of C4A protein is a primary risk factor for SLE disease susceptibility per se. On the other hand, Spanish, Mexican, Australian Aborigine SLE patients had increased frequencies of C4B deficiency instead of C4A deficiency. Such observations underscore the importance of both C4A and C4B proteins in the fine control of autoimmunity. Different racial and genetic backgrounds could change the thresholds for the requirement of C4A or C4B protein levels in immune tolerance and immune regulation. Most past epidemiological studies of C4 in human SLE did not consider the polygenic and gene size variations of C4A and C4B. In addition, many studies were overly dependent on phenotypic observations or methods that did not distinguish differential C4A and C4B protein expression caused by unequal gene number or different gene size from the absence of a functional C4A or C4B gene. For further longitudinal studies on clinical manifestations of SLE, it would be informative to stratify the patients with accurately defined C4A and C4B genotypes. Likewise, elucidation of epistatic genetic factors interacting with C4AQ0 would provide important insights into the intricate roles of C4 in SLE disease susceptibility and pathogenesis.

A human CR1-like transcript containing sequence for a binding protein for iC4 is expressed in hematopoietic and fetal lymphoid tissue

Primate immune adherence receptors are erythrocyte complement receptors (E-CR) that favorably influence the clearance of circulating immune complexes (IC). The human E-CR is the type one complement receptor (CR1), most commonly expressed as a 220 kDa protein containing 30 short consensus repeats (SCRs). The chimpanzee E-CR is a 75 kDa protein composed of eight SCRs, and is encoded by an ortholog of human CR1-like (CR1L), a genetic element related to CR1. Human CR1L was previously identified from genomic clones that predict exons for seven SCRs, and there have been no reports of CR1L expression. The purpose of this study was to determine if human CR1L is expressed. Amplification of human bone marrow cDNA using primers specific for CR1/CR1L yielded a product similar to chimp CR1L encoding sequence. The first 6.5 SCRs matched 100% with the predicted human CR1L sequence, while the second half of SCR 7 was homologous to the comparable chimp CR1L sequence but with a stop codon. Expression in COS-7 cells yielded a human CR1L protein of approximately 50 kDa that exhibited binding specificity for iC4 but not for iC3. Neither northern nor western blot analysis of human bone marrow revealed the presence of the CR1L transcript or protein. However, northern blot analysis of various other lymphoid tissue identified a candidate CR1L transcript in human fetal liver. PCR amplification of a cDNA panel of human fetal tissue confirmed the presence of the CR1L transcript in fetal liver, and to a lesser extent in fetal spleen and thymus. Thus, expression of the CR1L transcript appears to be limited to hematopoietic and fetal lymphoid tissue.

A CR1 polymorphism associated with constitutive erythrocyte CR1 levels affects binding to C4b but not C3b

The erythrocyte type one complement receptor (E-CR1) mediates erythrocyte binding of complement-opsonized immune complexes (IC), and helps protect against random deposition of circulating IC. Two linked CR1 polymorphisms occur in binding domains, at I643T and Q981H. In Caucasians, the variant alleles (643T, 981H) are associated with low constitutive E-CR1 expression levels. This study was conducted to determine if these polymorphisms affect ligand binding, and if so, represent risk factors for the autoimmune IC disease, systemic lupus erythematosus (SLE). In an ELISA comparing relative ligand binding differences, E-CR1 from individuals homozygous for the variant residues (643TT/981HH) exhibited greater binding to C4b, but not C3b, than homozygous wild-type E-CR1. Analysis of single-binding domain CR1 constructs demonstrated that the 981H residue imparted this enhanced C4b binding. No differences were observed in the 981H allele frequency between Caucasian controls (0.170, n = 100) and SLE patients (0.130, n = 150, P = 0.133), or between African American controls (0.169, n = 71) and SLE patients (0.157, n = 67). In a subset of individuals assessed for CR1 size, excluding from this analysis those expressing at least one B allele revealed a trend for over-representation of the 981H allele in Caucasian controls (0.231 frequency, n = 26) versus SLE patients (0.139, n = 83, P = 0.089), but again no difference between African American controls (0.188, n = 24) and SLE patients (0.191, n = 34). These data suggest that the 981H residue compensates for low constitutive expression of E-CR1 in Caucasians by enhancing C4b binding. This may contribute protection against SLE.

Of mice and men: the relevance of the mouse to the study of human SLE

A number of mouse models have been utilized to study the pathophysiology of immune complex (IC) disease, and the hallmark IC disease systemic lupus erythematosus (SLE). Many of these studies have provided exciting new insights into IC-mediated inflammation and autoimmunity. However, numerous differences exist between mice and humans that suggest that mouse studies are not always applicable to human disease. These differences can be found in the biological systems that interact with circulating IC, in the specifics of disease presentation, and in the general physiology of the two species. Furthermore, although the mechanisms of SLE-like autoimmune disease in the mouse are being defined through analyses of the murine models of SLE, it remains to be proven that these mechanisms are relevant to human SLE. Thus, generalizing the results of the mouse studies to human SLE and other human IC diseases must be done with caution.

Molecular identification of Knops blood group polymorphisms found in long homologous region D of complement receptor 1

Complement receptor 1 (CR1) has been implicated in rosetting of uninfected red blood cells to Plasmodium falciparum-infected cells, and rosette formation is associated with severe malaria. The Knops blood group (KN) is located on CR1 and some of these antigens, ie, McCoy (McC) and Swain-Langley (Sl(a)), show marked frequency differences between Caucasians and Africans. Thus, defining the molecular basis of these antigens may provide new insight into the mechanisms of P falciparum malaria. Monoclonal antibody epitope mapping and serologic inhibition studies using CR1 deletion constructs localized McC and Sl(a) to long homologous repeat D of CR1. Direct DNA sequencing of selected donors identified several single nucleotide polymorphisms in exon 29 coding for complement control protein modules 24 and 25. Two of these appeared to be blood group specific: McC associated with K1590E and Sl(a) with R1601G. These associations were confirmed by inhibition studies using allele-specific mutants. A sequence-specific oligonucleotide probe hybridization assay was developed to genotype several African populations and perform family inheritance studies. Concordance between the 1590 mutation and McC was 94%; that between Sl(a) and 1601 was 88%. All but 2 samples exhibiting discrepancies between the genotype and phenotype were found to be due to low red cell CR1 copy numbers, low or absent expression of some alleles, or heterozygosity combined with low normal levels of CR1. These data further explain the variability observed in previous serologic studies of CR1 and show that DNA and protein-based genetic studies will be needed to clarify the role of the KN antigens in malaria.

CR1 and CR1-like: the primate immune adherence receptors

Immune adherence describes the phenomenon in which complement-opsonized substrates, such as immune complexes (IC), viruses, or bacteria, are bound by primate erythrocytes via erythrocyte complement receptors. In vivo studies have shown that this binding allows the erythrocyte to act as an inert shuttle, targeting IC to the monocyte phagocytic system and away from vulnerable tissue. Thus, immune adherence appears to play an integral role in the primate in promoting the safe clearance of circulating IC and preventing IC-mediated pathologies. The complement receptors that mediate immune adherence comprise two unique but closely related gene products, either the type one complement receptor (CRI) in humans or CRI-like in non-human primates. This review focuses on the structure, function, and physiological role of the primate immune adherence receptors.

The chimpanzee and cynomolgus monkey erythrocyte immune adherence receptors are encoded by CR1-like genes

The human erythrocyte immune adherence (IA) receptor is the Mr 220,000 type one complement receptor, or CR1. Nonhuman primate IA receptors are comprised of a family of smaller erythrocyte complement receptors (E-CRs) of unknown origin. Recently, the Mr 65,000 baboon E-CR was identified as a glycophosphatidylinositol (GPI)-linked protein encoded by a partially duplicated CR1 gene termed CR1-like. The purpose of this study was to determine the genetic origin of the Mr 75,000 chimpanzee E-CR. Two previously identified cDNAs, an alternative splice product of CR1 termed CR1a and a chimpanzee form of CR1-like, were synthesized and amplified from chimpanzee bone marrow RNA, and transiently expressed in COS-7 cells. By SDS-PAGE, the CR1a protein had a relative mobility slightly greater than chimpanzee E-CR, whereas that of the CR1-like protein was slightly less. Affinity chromatography demonstrated that little chimpanzee CR1a bound to human C3i linked to activated thiol-Sepharose (C3i-ATS), while over 50% of both chimpanzee CR1-like and chimpanzee E-CR bound to C3i-ATS. Treatment with phosphatidylinositol-specific phospholipase C (PIPLC) to assess GPI linkage released E-CR from chimpanzee erythrocytes, and E-CR from cynomolgus monkey erythrocytes. Based on size, ligand-binding specificity, and PIPLC sensitivity, we conclude that the chimpanzee E-CR is encoded by the CR1-like gene. Furthermore, based on PIPLC sensitivity, the cynomolgus monkey E-CR is also likely encoded by a CR1-like sequence. Thus, CR1-like, which is a genetic element of unknown significance in humans, is the gene that encodes the erythrocyte IA receptor of many nonhuman primates.

Effects of immune complex formation and complement activation on circulating platelets in the primate

Primate platelets are different from rodent and rabbit platelets in that they do not express receptors for C3a or C5a or immune adherence receptors. This study assessed the effects of immune complex (IC)-induced complement activation on primate platelets in the circulation. Cynomolgus monkeys (CYN, N = 4) immunized to bovine gamma globulin (BGG) were infused with BGG over 5 min to induce acute intravascular IC formation and complement activation. The studies were carried out under normal complement conditions (N = 12), partial complement inhibition (CAB-2 treated, N = 3), or total complement inhibition (CVF treated, N = 1). Under normal complement conditions, BGG infusion increased C3a levels from undetectable to an average of 11.9 +/- 2.6 micrograms/ml. At this time, decreases occurring in both circulating neutrophils (85 +/- 6%) and monocytes (78 +/- 6%) were significantly greater than decreases in circulating platelets (13 +/- 3%, p < 0.001). Partial complement inhibition had an equivocal effect on the BGG-induced changes in circulating leukocytes, while total complement inhibition abrogated these changes. In contrast, platelet changes were unaffected by complement inhibition. We conclude that, compared to circulating leukocytes, circulating platelets are insensitive to intravascular complement activation induced by IC in the nonhuman primate. These results contrast with previous studies in rodents which demonstrate strong effects of IC-induced intravascular complement activation on both circulating neutrophils and platelets.

Prevention of acute murine cardiac allograft rejection: anti-CD4 or anti-vascular cell adhesion molecule one monoclonal antibodies block acute rejection but permit persistent graft-reactive alloimmunity and chronic tissue remodelling

We treated C57BL/6 mouse recipients of DBA/2 cardiac allografts with anti-CD4 monoclonal antibodies (mAb) or anti-vascular cell adhesion molecule 1 mAb to promote long-term allograft survival and subjected both the recipient animals and the long-surviving allografts to a battery of histologic and immunologic tests. The results were similar regardless of the mAb used for antirejection therapy. At all tested times after transplantation, the allografts displayed histologic evidence of ongoing microvascular endothelial activation and interstitial leukocytic infiltration. Reverse transcription polymerase chain reaction analyses revealed continuous intragraft expression of messenger RNA for interleukin 1, interleukin 2, interleukin 4, interleukin 6, tumor necrosis factor, interferon gamma, and transforming growth factor beta. All grafts had histologic evidence of ongoing vascular and parenchymal tissue remodeling, including interstitial fibrosis and vascular neointimal hyperplasia. The graft recipients retained limiting dilution analysis--detectable, donor-reactive cytolytic T lymphocyte, and helper T lymphocyte in their spleens and produced high liters of donor-reactive alloantibodies. Variable amounts of allogeneic microchimerism were detectable in some, but not all of the long-surviving graft recipients. In general, these observations indicate that (1) a similar immune status is achieved in long-surviving allografts and their recipients when either anti-CD4 mAb or anti-vascular cell adhesion molecule-1 mAb was used for antirejection therapy, in spite of the major differences in lineage and distribution of cells targeted by these two mAbs, (2) this immune status is characterized by continuous, long-term inflammatory and immune processes very similar to those observed during acute allograft rejection, and (3) in spite of these processes the allografts continue to function, although they invariably develop a chronic rejection-like histopathologic condition that may ultimately limit graft function. In this regard, the recipients of long-surviving allografts do not seem to be tolerant of their graft alloantigens.