Background In Systemic sclerosis, anti-CENP Ab positive patients (pts) are at higher risk of developing pulmonary hypertension compared to pts expressing other ANA specificities. In a previous investigation (1), IgG against the immunodominant epitope of CENP-A spanning amino acid 1-17 (peptide Ap1-17), were purified from sera of patient (pt) 4 and pt14 and used to isolate specific phage clones expressing peptide (pc). Pcs specific for Pt4 IgG (pc4s) and pt14 IgG (pc14s) displayed differential reactivity with anti-Ap1-17 IgG from other SSc pts (1,2), indicating they can distinguish different subsets within anti-CENP-A Ab population.
Objectives To assess the reactivity of sera from 84 anti-CENP-A Ab positive pts with pc4.1, pc4.2, pc14.1 and pc14.2, and to search for clinical correlates.
Methods Clinical and serological data were collected as previously described (2). Systolic pulmonary arterial pressure (sPAP) was measured using Doppler echocardiography. The reactivity and specificity of serum with pc was assessed by indirect ELISA using mouse anti-M13 mAb to capture pc to the plates and xeno-Ab to the Fc portion of human IgG to detect pc-bound sera IgG. Multivariate forward stepwise linear (or logistic) regression analysis was used to define a predictive association between a clinical variable and the levels of anti-pcs Ab.
Results Following a linear regression analysis, anti-pc4.2 and pc14.1 Ab were the only serological variables retained in the model able to predict sPAP and DLCO, albeit in a opposite way: an increased of anti-pc4.2 predicted a sPAP increase (p<0.001) and DLCO decrease (p=0.002), while an increase of anti-pc14.1 was associated to a sPAP decrease (p=0.015). Along the same line, anti-pc4.2 and anti-pc14.1 were associated to an increase and decrease score respectively of the Medsger severity scale item lung. Neither anti-Ap1-17 nor -Ap17-30 Ab (reflecting CENP specificity) were retained in the model for any clinical outcome variable included. To evaluate the strength of prediction of sPAP by anti-pc Ab, a forward stepwise logistic regression analysis was performed by including dichotomized sPAP (cut-off >45 mmHg) as outcome variable and anti-pc Ab as predictors, along with possible confounding factors namely gender, disease duration and age at diagnosis. Again, anti-pc4.2 and pc14.1 were retained in the model: positivity for sPAP was associated with high levels of anti-pc4.2 Ab (p=0.038), while negativity for sPAP was associate with high levels of anti-pc14.1 Ab (p=0.002).
Conclusions Overall the data indicate that patients expressing high levels of Ab to the sub-specificities of CENP-A defined by pc4.1 are at higher risk of developing pulmonary hypertension, whereas those expressing high levels of Ab to the specificity defined by pc14.1 are more protected from this complication.
Favoino, E. et al., 2013. Autoantibodies recognizing the amino terminal 1-17 segment of CENP-A display unique specificities in systemic sclerosis. PLoS. One. 8: e61453.
Perosa, F., et al., 2013. Clinical correlates of a subset of anti-CENP-A antibodies cross-reacting with FOXE3p53-62 in systemic sclerosis. Arthritis Res. Ther. 15: R72.
Acknowledgements This work was supported by a grant from the “Italian Group against Systemic Sclerosis” (GILS)
Disclosure of Interest None declared