Connective tissue activation. xxxvi. the origin, variety, distribution, and biologic fate of connective tissue activating peptide–iii isoforms: characteristics in patients with rheumatic, renal, and arterial disease

Objective. To determine the origin, distribution, and biologic fate of platelet‐derived connective tissue activating peptide–III (CTAP‐III), to define the relative amounts of the antigen forms (CTAP‐III, betathromboglobulin [β‐TG], neutrophil activating peptide–2 [NAP‐2]) in plasma of normal persons and those with rheumatic or end‐stage renal disease, and to define the isoforms of CTAP‐III in platelets, plasma, transudates, and tissue deposits. Methods. CTAP‐III in plasma was measured by enzyme‐linked immunosorbent assay, and growth promoting activity of CTAP‐III isoforms was tested in synovial and peritoneal cell cultures by measuring increased synthesis of ¹⁴C‐glycosaminoglycan (¹⁴C‐GAG) and ³H‐DNA. Isolated CTAP‐III was characterized by Western blotting, microsequencing, and mass spectrometry. Results. CTAP‐III was the primary isoform of this antigen family in normal platelets and platelet‐rich plasma; β‐TG and NAP‐2 accounted for <1% of CTAP‐III isoforms. Previously undescribed isoforms, i.e., CTAP‐III des 1, des 1–2, des 1–3, and a phosphate adduct of CTAP‐III, were observed in varying amounts. Elevated plasma levels of CTAP‐III antigen were found in a substantial fraction of rheumatic disease patients: 24% of those with rheumatoid arthritis, 36% of those with systemic sclerosis, and 15% of those with systemic lupus erythematosus. All 10 patients with end‐stage kidney disease had marked elevations of plasma CTAP‐III levels, which stimulated DNA and GAG synthesis by peritoneal cells in culture. Only large isoforms (such as CTAP‐III) were detected in venous plasma of normal subjects, rheumatic disease patients, and patients receiving long‐term dialysis. Normal human spleen and kidney contained substantial (μ/gm) amounts of CTAP‐III and traces of an isoform with the electrophoretic mobility of CTAP‐III des 1–15/NAP‐2. Liver, lung, and urine contained lesser (ng/gm) amounts of CTAP‐III. Conclusion. These data show that, among the 10 known isoforms, intact CTAP‐III itself was the major circulating isoform (>90%), and β‐TG was the most rare (0–1%). Deposition of CTAP‐III in tissues, such as synovium, spleen, and kidney, is associated with partial processing to NAP‐2–like isoforms and the potential to induce neutrophil and fibroblast activation in patients with rheumatic or end‐stage renal disease.