Anti–cyclic citrullinated peptide antibodies in psoriasis patients without arthritis

The Prevalence of Anticitrullinated Protein Antibodies in Older Poles-Results from a Population-Based PolSenior Study

Little is known about the occurrence of antibodies in older subjects. We analyzed the prevalence of anticitrullinated protein antibodies (anti-CCP) in a representative cohort of Polish older adults, participants of PolSenior substudy. Randomly selected 1537 serum samples of community-dwelling participants aged 65 and over. Questionnaires were completed by qualified interviewers and laboratory assessments served as a database for this analysis. The frequency of anti-CCP seropositivity (N = 50) was estimated at 3.25% (95% CI: 2.45-4.30%), being higher among women-4.05% (2.83-5.73%) than men-2.41% (1.48-3.86%). The frequency of anti-CCP seropositivity was decreasing with age from 4.29% in aged 65-74 years and 4.07% in 70-84 years to 1.50% in aged 85 years or above (p < 0.05). Hypoalbuminemia, inflammatory status (C-reactive protein >10 mg/dL or interleukin-6 ≥10 pg/mL), and female gender were associated with increased, while age ≥85 years with decreased risk of seropositivity. Multivariable logistic regression revealed that hypoalbuminemia, inflammatory status, and age ≥85 years were independently associated factors of anti-CCP seropositivity. The decreased frequency of anti-CCP seropositivity in the oldest old suggests shorter survival of the seropositive individuals who developed rheumatoid arthritis. It seems that low symptomatic RA remains frequently undiagnosed in older subjects.

The Clinical Application of Anti-CCP in Rheumatoid Arthritis and Other Rheumatic Diseases

Rheumatoid arthritis (RA) is a common rheumatic disease in Caucasians and in other ethnic groups. Diagnosis is mainly based on clinical features. Before 1998, the only serological laboratory test that could contribute to the diagnosis was that for rheumatoid factor (RF). The disease activity markers for the evaluation of clinical symptoms or treatment outcome were the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). As a matter of fact, the diagnosis of early RA is quite impossible, as the clinical criteria are insufficient at the beginning stage of the disease. In 1998, Schelleken reported that a high percentage of RA patients had a specific antibody that could interact with a synthetic peptide which contained the amino acid citrulline. The high specificity (98%) for RA of this new serological marker, anti-cyclic citrullinated antibody (anti-CCP antibody), can be detected early in RA, before the typical clinical features appear. The presence or absence of this antibody can easily distinguish other rheumatic diseases from RA. Additionally, the titer of anti-CCP can be used to predict the prognosis and treatment outcome after DMARDs or biological therapy. Therefore, with improvement of sensitivity, the anti-CCP antibody will be widely used as a routine laboratory test in the clinical practice for RA.

Significance of Anti-cyclic Citrullinated Peptide Autoantibodies in Immune-mediated Inflammatory Skin Disorders with and without Arthritis

Background:

Anti-cyclic citrullinated peptides (CCPs) are autoantibodies directed against citrullinated peptides. Rheumatoid factor (RF), an antibody against the Fc portion of IgG, is known to form immune complexes and contribute to the etiopathogenesis of various skin disorders. C-reactive protein (CRP), an acute-phase protein, increases following secretion of interleukin-6 from macrophages and T cells. Anti-CCP, RF, and CRP are well-established immune-markers, their diagnostic potential in immune-mediated skin disorders remains less widely studied.

Aims and Objectives:

To determine the correlation between anti-CCP, RF, and CRP in immune-mediated inflammatory skin diseases.

Materials and Methods:

About 61 clinically diagnosed cases of various immune-mediated skin diseases (psoriasis [n = 38], connective tissue diseases such as systemic lupus erythematosus and systemic sclerosis [n = 14], and immunobullous disorders including pemphigus vulgaris and pemphigus foliaceus [n = 9]) were included in the study. These patients were subclassified on the basis of presence or absence of arthritis. Arthritis was present in nine cases of psoriasis and seven connective tissue disorder patients. Detection of serum anti-CCP was done using enzyme-linked immunosorbent assay, whereas CRP and RF levels were detected using latex agglutination technique.

Results:

Of the 61 specimens, 14.75% had elevated serum anti-CCP levels. RF and CRP levels were elevated in 18.03% and 39.34% specimens, respectively. RF was elevated in 13.16% of inflammatory and 42.88% of connective tissue disorders, whereas anti-CCP was raised in 10.53% of inflammatory and 35.71% of connective tissue disorders. CRP positivity was highest in connective tissue disorders (50%), followed by 39.47% in inflammatory and 22.22% in immunobullous conditions. In none of the immunobullous patients, anti-CCP or RF levels were found to be elevated. Association of the presence of arthritis with elevated anti-CCP was found to be statistically significant.

Conclusions:

Although anti-CCP, RF, and CRP levels are valuable markers of chronic immune-mediated skin disorders, elaborate studies enrolling a larger number of patients are required to validate these diagnostic markers.

Immune response to chemically modified proteome

Both enzymatic and nonenzymatic PTMs of proteins involve chemical modifications. Some of these modifications are prerequisite for the normal functioning of cell, while other chemical modifications render the proteins as "neo-self" antigens, which are recognized as "non-self" leading to aberrant cellular and humoral immune responses. However, these modifications could be a secondary effect of autoimmune diseases, as in the case of type I diabetes, hyperglycemia leads to protein glycation. The enigma of chemical modifications and immune response is akin to the "chick-and-egg" paradox. Nevertheless, chemical modifications regulate immune response. In some of the well-known autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, and multiple sclerosis, chemically modified proteins act as autoantigens forming immune complexes. In some instances, chemical modifications are also involved in regulating immune response during pathogen infection. Further, the usefulness of proteomic analysis of immune complexes is briefly discussed.