Autoantibodies to keratin in Sjögren's syndrome

The adaptive immune response to porous regenerated keratin as a bone graft substitute in an ovine model

Reconstituted keratin is a novel bone graft material when prepared as a rigid scaffold. Understanding the immunogenicity of this material is important to determine whether this substance is a viable surgical option. Previous studies have shown no innate immune system activation in response to reconstituted keratin implants. To examine antibody-mediated immune responses to reconstituted keratin implants, bone and blood samples were taken from twelve sheep with surgically created tibial defects containing such implants. RT-PCR was used to detect mRNA of the inflammatory marker SOCS 3 in local bony tissue, and a novel immunohistochemistry assay developed to detect antikeratin antibodies in serum. Two animals were sacrificed per time-point at weeks 1, 2, 4, 6, 8 and 12. Time points for serum analysis included baseline (pre-surgery) and all other time points; mRNA analysis examined samples from all time points. No upregulation in antikeratin antibodies or SOCS 3 mRNA was observed at any time point, indicating that reconstituted keratin implants do not trigger an adaptive immune response in vivo in an ovine model. These findings provide the platform for further development of keratin implants in other mammalian models to define its immunogenic profile and safety.

Anti-cytoplasmic autoantibodies reactive with epithelial cells of the salivary gland in sera from patients with Sjögren's syndrome: their disease- and organ-specificities

To test whether the autoantibodies reactive with epithelial cells of the salivary gland in sera from Sjögren's syndrome (SS) patients are specific for the organ and the disease, tissue reactivities of serum IgG obtained from the patients with SS and oral lichen planus (OLP), another immune-mediated oral mucosal disease, were examined by immunohistochemistry and Western blotting. IgG purified from the sera of SS patients specifically localized not only on the nuclei but also on the cytoplasm of the salivary gland epithelial cells. On the other hand, no convincing staining of the epithelial cells was observed when IgG purified from the sera of OLP patients or those from healthy controls were used for immunohistochemistry. No cytoplasmic staining was observed when sections of kidneys and pancreas were stained with SS patients' IgG. In Western blotting performed by using lysates of a submandibular gland as antigens, all the IgG prepared from the SS patients reacted prominently with several protein bands, including those specific for the disease and the organ. These results suggest that production of autoantibodies reacting with the cytoplasm of salivary gland epithelial cells is a characteristic of SS, and may play a role in the pathogenesis of the sialadenitis.

Antibodies to cytokeratins in inflammatory arthropathies

OBJECTIVES

Cytokeratins are a major constituent of the cytoskeleton in eukaryotic cells and are vital for the maintenance of cell structure and function. Identification of increased levels of IgA antibodies to these intracellular structures has prompted increasing interest in the potential role between the gut and the immune system in the pathogenesis of inflammatory arthritis. This review examines the salient features of cytokeratin (CK) antibodies that are relevant to inflammatory arthropathies and discusses the meaning and potential applications of these findings in the context of the different arthropathies.

METHODS

Review of the literature on antibodies to cytokeratins in inflammatory arthropathies, using MEDLINE and the key words (cyto)keratin and arthritis. The studies were interpreted and critiqued.

RESULTS

Increased levels of IgA antibodies to CK-18 and epidermal keratins have been shown by enzyme-linked immunosorbent assay (ELISA) in rheumatoid arthritis and psoriatic arthritis. Levels were not increased in osteoarthritis or reactive arthritis.

CONCLUSIONS

CK-18 is present within endothelial cells lining synovial blood vessels in patients with various rheumatic conditions, including rheumatoid arthritis, as well as in normal controls. Damage to synovial endothelial cells may lead to increased production of antibodies to CK-18. The CK antibody response is independent of the polyclonal immunoglobulin expansion typical of RA and is not specific for RA because an increased IgA response to CK-18 also has been shown in psoriasis and in psoriatic arthritis. Damage to synovial endothelial cells does not explain the increased autoantibody production in other conditions such as psoriasis. In this condition, damage to epithelial tissues in other regions of the body (e.g, skin, gut, kidney) may lead to production of keratin antibodies that recognize epitopes common to all CK, including CK-18. The reason for an elevated IgA anti-CK response rather than an IgG or IgM response is not clear. It cannot be explained by a general increase in serum IgA levels. Most of the conditions in which raised levels of these antibodies were found have been associated to different degrees with abnormalities of the gut mucosa or mucosal immune system. It appears that the nature of autoantibodies to CK-18 is probably natural rather than pathogenic. Currently there are no data on the source of the IgA antibodies to cytokeratins (i.e., mucosal or central immune system). Indeed, it may depend on the disease.

Increased levels of IgA antibodies to cytokeratin-18 and epidermal keratin in rheumatoid arthritis

OBJECTIVE

To investigate whether levels of antibodies to cytokeratin-18 (CK-18) and epidermal keratin (EPK) were raised in patients with rheumatoid arthritis (RA).

METHODS

We measured antibodies to CK-18 and EPK in patients with RA and in patients with osteoarthritis (OA), as well as in normal control subjects by means of an enzyme-linked immunosorbent assay.

RESULTS

IgA antibodies to both CK-18 and EPK were significantly increased in patients with RA compared with the controls and with patients with OA (P < 0.0001). No difference was noted in the levels of IgG or IgM antibodies to CK-18 or EPK between controls and patients with OA or RA.

CONCLUSION

Raised levels of IgA autoantibody to CK-18 and EPK may reflect damage to cytokeratin-containing cells (e.g., in synovial endothelium) and could be a useful disease marker in RA.

Immunohistochemical demonstration of enamel proteins in odontogenic tumors

Immunohistochemical localization of two enamel proteins, amelogenin and enamelin, in comparison with that of keratin, was determined in odontogenic tumors and the allied lesions in order to verify functional differentiation of the tumor cells as ameloblasts. Amelogenin and enamelin were demonstrated in small mineralized foci and in the tumor cells surrounding them in adenomatoid odontogenic tumor (AOT), calcifying epithelial odontogenic tumor (CEOT), and calcifying odontogenic cyst (COC). Hyaline droplets in AOT showed positive staining for both enamel proteins. These mineralized and hyaline materials were not positive for keratin, although tumor cells were positive. On the other hand, no immunoreaction for enamel proteins was obtained in ameloblastoima and odontogenic epithelial cell nests within myxoma and epulis. The results suggest that tumor cells of AOT and CEOT and lining epithelial cells of COC show ameloblastic differentiation in part, but that ameloblastoma cells do not attain functional matauration as secretory phase ameloblasts.