Histologic and electron microscopic characterization of the antiperinuclear factor antigen

Abstract

The presence of the antiperinuclear factor, an autoantibody that recognizes cytoplasmic antigens, was detected in sera from patients with rheumatoid arthritis (59%), seronegative rheumatoid arthritis (36%), systemic lupus erythematosus (46%), systemic sclerosis (a%), and in nonautoimmune controls (10%). The antigenic perinuclear granules were found in the stratum intermedium layer of the buccal mucosa. Granules exhibited histologic features of nucleoproteins, stained for ribonucleoprotein, and showed the ultrastructural characteristics of aggregated rough endoplasmic reticulum. The antiperinuclear factor may recognize a common autoantigen in connective tissue disease.Rheumatoid arthritis (RA) patients, similar to those with related disorders, can form a variety of autoantibodies against nuclear, cytoplasmic, and tissue-specific antigens ( 1,2). Antiperinuclear factor (APF). first described in the mid-1960s by Nienhuis and Mandema (3). is an autoantibody that recognizes cytoplasmic granules in human buccal mucosal cells. geneous-appearing granules, 0.54.0 pm in diameter, located in the cytoplasm around the nucleus. Investigators have found APF in the sera of 50436% of RA patients (4-15), 31-3% of patients with Sjogren's syndrome (5,9,13), as many as 10% of healthy controls, and rarely in other rheumatic disease patients (3-7). A recent study suggested that APF determination in rheumatic disease patients by indirect immunofluorescence had a sensitivity and specificity for RA of 86% and 96%. respectively (7). The presence of APF correlates most closely with the presence of rheumatoid factor and rheumatoid nodules, but the antibody has also been detected in 37-76% of patients with seronegative RA (5-8).The APF antibody binds to cytoplasmic granules in human buccal mucosal cells, which have presumptively been termed "keratohyaline granules" (4.16) based on their rough histologic resemblance to the keratohyaline bodies in the stratum granulosum of human epidermis. The biologic and biochemical nature of the APF-reactive granules is unknown. Attempts to characterize the antigen have thus far been hampered by a lack of availability of suitable human donors (5-7) or alternate animal tissue substrates for the assay (16). However, independent studies in oral medicine (17-20) have documented the presence of at least 3 types of cytoplasmic granules in human oral keratinocytes, including "membrane-coated" granules, "epidermaltype" keratohyaline granules, and "buccal-type'' keratohyaline granules; these findings have not been related to the APF antigen.In this report, we extend our preliminary observations regarding the prevalence of APF in various rheumatic diseases (21) and the staining characteristics of the perinuclear antigen-containing granules (22). The diagnostic specificity of the APF assay (by indi-

Anti-perinuclear Factor as Diagnostic Marker in Rheumatoid Arthritis

“…This dilution was the most proper proposed titer for APF test. Also, in the performed studies APF were observed in RA patients with sensitivity 36-87% [7][8][9][10][11][12] and specificity 73-100% [9][10][11]. Furthermore, APF was a valuable serological tool for the diagnosis of RA disease and a useful serological marker to differentiate of disease from the other rheumatic disease (p=0.05) [Table/ Fig-4] [9,10].…”

“…Due to sensitivity of (36 -87%) [7][8][9][10][11][12] and high specificity of (73-100%) [10,11] is a valuable serological tool for the diagnosis of the disease [7,10] and a useful serological marker to differentiate this disease from the other inflammatory rheumatoid diseases [9].…”

“…This Ab binds to cytoplasmic granules in human buccal mucosal cells and on the basis of their histologic similarity with keratohyaline bodies in the stratum granulosum of human epidermis, known as keratohyalin granules [12]. It is an insoluble protein sensitive to freezing and its antingenicity reduces the different methods of fixation.…”

The antiperinuclear factor and the so-called antikeratin antibodies are the same rheumatoid arthritis-specific autoantibodies.

“…Among them, rheumatoid factors have been the most extensively studied (reviewed in reference 1), but numerous other autoantibodies such as anticollagen (2), antinuclear (3,4), and anticytoskeletal (5) antibodies have been described. A lot of work has also been performed on the antiperinuclear factor (APF)' (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)) and on the antikeratin antibodies (AKA) (9,(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37). Both these antibodies have been demonstrated to be highly specific serological markers of the disease and therefore are increasingly used for the diagnosis of RA (reviewed in reference 38).…”

“…The APF-defined antigen has not been identified yet. However, the ultrastructural and histochemical properties of the granules (8,17) and the sensitivity of APF assay to various enzymatic or chemical treatments of the cells ( 19) indicate that the granules correspond to keratohyalin granules and that the antigen is not composed of nucleic acids, but is rather a protein component sensitive to fixatives such as acetone and methanol and to freeze-thawing cycles.…”