The penetrating potential of autoantibodies into live cells in vitro coincides with the in vivo staining of epidermal nuclei

Expression of caveolin family proteins in serum of patients with systemic lupus erythematosus

OBJECTIVES

Caveolin family proteins, including caveolin-1 (Cav-1), caveolin-2 (Cav-2), and caveolin-3 (Cav-3), are identified as the principal protein components of caveolae in mammalian cells. Circulating form of caveolin family proteins can be used as a good potential biomarker for predicting disease.

METHODS

To investigate the clinical significance of the serological levels of caveolin family proteins in patients with systemic lupus erythematosus (SLE), we evaluated the soluble serum levels of caveolin family proteins in patients with SLE by enzyme-linked immunosorbent assay (ELISA) and assessed their associations with various known clinical variables.

RESULTS

The major findings of our study are as follows: Cav-2 was not detected in serum of SLE patients and normal controls (NCs). Serum Cav-1 and Cav-3 levels were higher in SLE patients compared with NCs. There were no significant correlations between serum Cav-1 and Cav-3 levels and SLE disease activity. Further analysis showed that serum Cav-3 may be more valuable as a marker than serum Cav-1 in SLE patients.

CONCLUSION

Serum levels of Cav-1 and Cav-3 might have a diagnostic role in patients with SLE. However, their predictive and prognostic value was not determined. Further studies are necessary to determine the potential clinical significance of these assays in SLE.

Identification of a Novel Non-desmoglein Autoantigen in Pemphigus Vulgaris

Pemphigus vulgaris (PV) is an autoimmune bullous disease of the skin and mucous membranes characterized by the presence of circulating and tissue-bound autoantibodies against keratinocyte cell surface antigens, specifically desmoglein (Dsg) 1 and 3. The pathogenic role of anti-Dsg antibodies is well-established, while the mechanism of blister formation is only partly defined. We have applied a previously developed method for the efficient immortalization of IgG+ memory B cells to identify novel target antigens in PV. A human monoclonal antibody reactive with a hitherto unreported non-Dsg antigen was isolated. Immunoprecipitation and immunoblotting studies with keratinocyte extracts indicated α-catenin as the putative antigen, then confirmed by immunoblotting on the recombinant protein. Four of ten PV sera reacted with recombinant α-catenin. Although the isolated human monoclonal antibody was per se unable to dissociate keratinocyte monolayers and also to synergize with a pathogenic antibody in vitro, further studies are warranted to assess its possible in vivo contribution in the multifactorial pathogenesis and heterogeneous manifestations of PV disease.

Antimitochondrial autoantibodies in pemphigus vulgaris: a missing link in disease pathophysiology

A loss of epidermal cohesion in pemphigus vulgaris (PV) results from autoantibody action on keratinocytes (KCs) activating the signaling kinases and executioner caspases that damage KCs, causing their shrinkage, detachment from neighboring cells, and rounding up (apoptolysis). In this study, we found that PV antibody binding leads to activation of epidermal growth factor receptor kinase, Src, p38 MAPK, and JNK in KCs with time pattern variations from patient to patient. Both extrinsic and intrinsic apoptotic pathways were also activated. Although Fas ligand neutralizing antibody could inhibit the former pathway, the mechanism of activation of the latter remained unknown. PV antibodies increased cytochrome c release, suggesting damage to mitochondria. The immunoblotting experiments revealed penetration of PVIgG into the subcellular mitochondrial fraction. The antimitochondrial antibodies from different PV patients recognized distinct combinations of antigens with apparent molecular sizes of 25, 30, 35, 57, 60, and 100 kDa. Antimitochondrial antibodies were pathogenic because their absorption abolished the ability of PVIgG to cause keratinocyte detachment both in vitro and in vivo. The downstream signaling of antimitochondrial antibodies involved JNK and late p38 MAPK activation, whereas the signaling of anti-desmoglein 3 (Dsg3) antibody involved JNK and biphasic p38 MAPK activation. Using KCs grown from Dsg3(-/-) mice, we determined that Dsg3 did not serve as a surrogate antigen allowing antimitochondrial antibodies to enter KCs. The PVIgG-induced activation of epidermal growth factor receptor and Src was affected neither in Dsg3(-/-) KCs nor due to absorption of antimitochondrial antibodies. These results demonstrated that apoptolysis in PV is a complex process initiated by at least three classes of autoantibodies directed against desmosomal, mitochondrial, and other keratinocyte self-antigens. These autoantibodies synergize with the proapoptotic serum and tissue factors to trigger both extrinsic and intrinsic pathways of cell death and break the epidermal cohesion, leading to blisters. Further elucidation of the primary signaling events downstream of PV autoantigens will be crucial for the development of a more successful therapy for PV patients.

Pathogenic autoantibodies: emerging insights into tissue injury

Accumulating evidence is emerging that B lymphocytes and autoantibodies are critical in the development of autoimmune disease. Even in certain disorders initially thought to be T cell-mediated, these immune components are now considered key players in the disease pathogenesis, and new autoantibody specificities have been added to the growing list of targets including cell surface receptors and ion channels that may be involved in a variety of neuropsychiatric and cardiovascular disorders. Studies of autoantibodies penetrating living cells suggest a dosage effect in generating a biological outcome in vivo. Some autoantibodies, such as those directed to double-stranded DNA, can bind to a variety of surrogate antigens located in different cellular compartments, and this may have different biological consequences. This polyreactive behavior could be related to their conformational diversity, or to the fact that the epitope recognized is distributed among other macromolecular antigens. In addition, recent studies revealed unsuspected mechanisms of pathogenesis, wherein autoantibodies have been described that can activate neuronal, endothelial cells or B lymphocytes. Other autoantibodies inactivate the target antigens, or exhibit a catalytic activity, releasing toxic oxygen products that may be linked to arthritic or atherosclerotic injury.

Nuclear localizing anti-DNA antibodies enter cells via caveoli and modulate expression of caveolin and p53

After administration to normal mice, a subset of monoclonal (m) anti-DNA antibodies (Ab) derived from MRL-lpr/lpr mice was identified that enter cells, in vivo. In the kidneys, this was associated with glomerular hypercellularity and proteinuria. In cultured cells, the same mAb bound to myosin 1 on the cell surface, prior to internalization, nuclear localization and inhibition of apoptosis. The present study focuses on the mechanisms underlying the observed functional effects. Subcellular localization studies revealed that following internalization, a prototypic, nuclear localizing, m antibody (Ab; termed H7) co-localized with myosin 1, shortly after internalization, within caveolae, near the cell membrane. Cell fractionation studies confirmed the presence of both H7 and myosin within the caveolar fraction. Since variations in caveolin protein expression have been associated with apoptotic events in cancer cells, through p53 dependent and independent pathways, modulation of caveolin by intracellular H7 was evaluated. Cellular entry of the anti-DNA Ab resulted in an increase in caveolin protein expression. Furthermore, after exposure of cells to dexamethasone to induce apoptosis, the usual increase in p53 was inhibited in the presence of intracellular H7. Taken together, the results suggest that upregulation of caveolin and inhibition of p53 induction are involved in H7-induced, inhibition of apoptosis. Furthermore, they suggest that this inhibition contributes to the glomerular hypercellularity observed in normal mice with intranuclear H7. The results also raise the possibility that inhibition of apoptotic pathways during inflammation or/and autoimmunity could influence subsequent disease events. The novel mechanism of cellular perturbation is indirect and dependent on apoptotic stimuli, and it may account for the presence of intranuclear antibodies in inflammatory and normal tissues of individuals with lupus.

Anti-idiotype antibodies abrogate the tissue deposition of anti-RNP human autoantibodies injected into neonatal BALB/c mice

OBJECTIVE

The goals of the current work are: 1) to examine the epidermal deposition of anti-RNP IgG human autoantibodies in neonatal BALB/c mice; 2) to look for immunoregulatory effects of anti-idiotypes allowing one to inhibit the epidermal deposition of anti-RNP antibodies; and 3) to elicit antinuclear antibodies in adult BALB/c mice by internal images of anti-idiotypes.

MATERIALS AND METHODS

Anti-idiotype antibodies were produced with human anti-RNP IgG obtained by ion exchange chromatography; F(ab')2 fragments were recovered from pepsin digestion and were purified using Sephacryl S-300. F(ab')2 fragments were then used to immunize New Zealand rabbits.

RESULTS

The anti-RNP IgG recognized the 70 kDa protein and the A (31 kDa) and C (19 kDa) proteins, while the anti-idiotype antibody specifically recognized the light or heavy chain of the anti-RNP (Fab')2 fragments. Additionally, anti-idiotypes recognized the anti-RNP IgG from some sera, but not the IgG from other specificities or from normal IgG. When anti-RNP IgG was injected intraperitoneally into BALB/c mice it induced immune complex deposition in the epidermis and at the dermal-epidermal junction. Previous injection of anti-idiotype antibodies abrogated the anti-RNP IgG deposits. Vaccination with anti-idiotypes elicit antinuclear antibodies in adult BALB/c mice.

CONCLUSIONS

Anti-idiotype antibodies abrogate in vitro the antinuclear antibody deposition in neonatal BALB/c mice. Anti-idiotype antibodies elicit antinuclear antibodies in adult BALB/c mice.

Mercury-induced anti-nucleolar autoantibodies can transgress the membrane of living cells in vivo and in vitro

Treatment with HgCl2 induces a systemic autoimmune disease in certain mice and rats. The major characteristic of this disease in mice with H-2s genotype is the production of anti-nucleolar autoantibodies (ANoIA). The exact mechanism(s) for the production and the functional role of mercury-induced ANoIA are not known. We have studied the ability of mercury-induced ANoIA to enter the living cells in vivo and in vitro. We found that in highly susceptible mice, treatment with mercury induced ANoIA capable of localizing in the nucleoli of kidney and liver cells in vivo. No detectable nucleoli localization of ANoIA were found in the cells of the heart, stomach, intestine and spleen. Consistent with the in vivo studies, mercury-induced ANoIA were also able to enter and translocate in the nucleoli of certain cells in vitro. The highest degree of antibody penetration was found in A-498 cells (a human kidney cell line) followed by 3T3 cells (a mouse fibroblast cell line), whereas the cells of lymphoid origin exhibited a very low degree of antibody penetration. Penetrated ANoIA could be recovered from the nucleoli of live 3T3 cells previously treated with ANoIA. The in vitro nucleolar translocation by ANoIA did not affect the DNA synthesis, but was found to be an active process dependent on time and temperature. Furthermore, pre-treatment of living cells with trypsin markedly inhibited both cell entry and nucleolar accumulation of ANoIA. Thus, mercury-induced ANoIA have a unique ability to transgress the membrane of certain living cells in vivo and in vitro, and to localize in the nucleoli.