Inflammatory plasma protein levels are elevated years before sarcoidosis diagnosis: a nested case-control study in Sweden

Abstract

Background: Sarcoidosis is an immune-mediated inflammatory disease whose natural development is not well understood. We aimed to determine if inflammatory plasma protein levels are elevated before sarcoidosis diagnosis compared to controls. Furthermore, we investigated which proteins are increased and how long before diagnosis they are increased.

Methods: Cases with sarcoidosis and controls matched 2:1 on sex, birthdate, subcohort and sample date were identified in the Northern Sweden Health and Disease Study to perform a nested case-control study. Cases were validated and included if they provided one or more plasma samples at least 2 years before sarcoidosis diagnosis. Plasma protein levels were measured using the Olink Inflammation panel and expressed in normalised protein expression values. Unconditional logistic regression models adjusted for age, sex, subcohort and time since sampling were used to estimate log odds ratios with 95% confidence intervals for each protein overall and by time to diagnosis. p-values were adjusted for multiple comparisons using the Benjamini-Hochberg method.

Results: We included 152 cases and 341 controls. Mean time between sample and sarcoidosis diagnosis was 13.4 years. 44 proteins were significantly elevated prior to sarcoidosis compared to controls in multivariable-adjusted analyses. The 10 proteins with the lowest p-values were CCL-3, CCL-19, cub domain-containing protein 1, CXCL9, CXCL10, interferon-γ, interleukin-12B, monocyte chemoattractant protein-3, tumour necrosis factor (TNF), and TNF receptor superfamily 9. Fewer proteins were associated with sarcoidosis in samples taken longer before diagnosis. Restricting to samples taken ≥10 years prior to sarcoidosis diagnosis, 27 proteins remained statistically significant.

Conclusion: Several inflammatory proteins were elevated in plasma many years before sarcoidosis onset compared to controls, revealing a pre-clinical phase characterised by inflammation.

Overview of the study. CDCP: cub domain-containing protein; IFN: interferon; MCP: monocyte chemoattractant protein; TNF: tumour necrosis factor; IL: interleukin; TNFRSF: TNF receptor superfamily.

FIGURE 1

Study design and flow chart depicting how sarcoidosis cases and matched controls were selected using risk set sampling from the population-based cohort Northern Sweden Health and Disease Study. All individuals included in this study provided at least one blood sample (stored in the Northern Sweden Biobank). Some provided two or three samples. Medical records of sarcoidosis cases diagnosed at Umeå University Hospital (Umeå, Sweden) were validated and included if diagnosis occurred after blood sample collection. Controls were matched on age, sex, subcohort and date of blood sample in a ratio of 2:1. Some individuals had a longer time between sample and diagnosis (e.g. case 3) and others had a shorter time (e.g. case 1, third sample). Samples taken within 2 years of sarcoidosis diagnosis were excluded (e.g. the second sample for case 2 was excluded). The primary study population included 152 sarcoidosis cases and 341 matched controls. Four sensitivity analyses were conducted in restricted study populations to address potential biases. BMI: body mass index.

FIGURE 2

Volcano plot showing the mean difference in normalised protein expression values between cases and controls (x-axis) and p-value (adjusted with Benjamini–Hochberg method, y-axis). The top 10 proteins are marked. A full list is presented in supplementary table S3. CDCP: cub domain-containing protein; IFN: interferon; MCP: monocyte chemoattractant protein; CCL: chemokine (C-C motif) ligand; TNF: tumour necrosis factor; IL: interleukin; TNFRSF: TNF receptor superfamily.

FIGURE 3

Log odds ratios (95% confidence intervals) of sarcoidosis associated with each protein estimated from logistic regression adjusted for age, sex, subcohort and time from sampling until diagnosis/index date. A log odds ratio >0 indicates a positive association between the protein and pre-clinical sarcoidosis. CSF: colony stimulating factor; Flt3L: FMS-related tyrosine kinase 3 ligand; HGF: hepatocyte growth factor; GDNF: glial cell line derived neurotrophic factor; TNFRSF: tumour necrosis factor receptor superfamily; IL: interleukin; CDCP: cub domain-containing protein; CCL: chemokine (C-C motif) ligand; MCP: monocyte chemoattractant protein; IFN: interferon; TNF: tumour necrosis factor.

FIGURE 4

Results from logistic regression models adjusted for age, sex, subcohort and time since sampling indicating the statistical significance (adjusted p<0.05) and the strength of the association between each protein and pre-clinical sarcoidosis. p-values were adjusted for multiple testing based on the Benjamini–Hochberg method. BMI: body mass index; CCL: chemokine (C-C motif) ligand; CDCP: cub domain-containing protein; CSF: colony stimulating factor; Flt3L: FMS-related tyrosine kinase 3 ligand; GDNF: glial cell line derived neurotrophic factor; HGF: hepatocyte growth factor; IFN: interferon; IL: interleukin; MCP: monocyte chemoattractant protein; TNF: tumour necrosis factor; TNFRSF: TNF receptor superfamily.

FIGURE 5

Number of proteins significantly associated with pre-clinical sarcoidosis when restricting the time period from sample to diagnosis. Results from logistic regression models examining 92 proteins adjusted for age, sex, subcohort and time since sampling.

FIGURE 6

Results from logistic regression models adjusted for age, sex, subcohort and time since sampling by time from blood sample to diagnosis indicating the statistical significance (adjusted p<0.05) and the strength of the association between each protein and pre-clinical sarcoidosis. p-values were adjusted for multiple testing based on the Benjamini–Hochberg method. CCL: chemokine (C-C motif) ligand; CDCP: cub domain-containing protein; CSF: colony stimulating factor; Flt3L: FMS-related tyrosine kinase 3 ligand; GDNF: glial cell line derived neurotrophic factor; HGF: hepatocyte growth factor; IFN: interferon; IL: interleukin; MCP: monocyte chemoattractant protein; TNF: tumour necrosis factor; TNFRSF: TNF receptor superfamily.