PUVA treatment of human cultured fibroblasts from psoriatic skin enhances the binding of antibodies to SSA(Ro)

Immunological aspects of congenital atrioventricular block

Isolated congenital heart block (CHB) in children is strongly associated with the occurrence of autoantibodies to Ro/SS-A and La/SS-B in the circulation of the mother. Although these antibodies are generally found in patients with generalized autoimmune diseases, they may also occur in symptomless mothers of CHB patients. It is thought that anti-Ro/SS-A and anti-La/SS-B may reach the fetal circulation via transplacental transport, starting around the 20th week of gestation. Although several hypotheses have been put forward, the exact mechanism through which these autoantibodies bind the fetal conduction system and elicit a local inflammatory response is still unclear. Also, the induction of the autoantibody response in the mother remains largely obscure, although a putative role of viral infection has been suggested. In this overview, the structure of the involved antigens will be discussed, followed by the nature of the antibodies. Recent data regarding the etiology of the anti-Ro/SS-A and anti-La/SS-B response and the role of these autoantibodies in the pathogenesis of CHB will be presented.

Ro/SS-A and La/SS-B: autoantigens in Sjögren's syndrome?

Sjögren's syndrome is characterized serologically by the presence of autoantibodies against Ro/SS-A and La/SS-B. The mechanisms by which these autoantibodies arise is not clear at this moment. B cells capable of producing antibodies to Ro/SS-A and La/SS-B seem to be present in every individual; whether or not an individual indeed makes these antibodies is governed by T cells. Recent experiments from us and from others indicate that T cell tolerance towards Ro/SS-A and La/SS-B can be broken by immunization of normal mice with recombinant human Ro/SS-A or La/SS-B. The specificity of the T cells directing the anti-Ro/SS-A and anti-La/SS-B autoantibody response in these animals has not yet been elucidated. T cells may either be directed against foreign epitopes present on the human immunogen or they may be truly autoreactive. In patients with Sjögren's syndrome, a comparable immunization route might encompass product of viral origin directing the T cell response via RNA/protein complexes. Putative candidates comprise viruses that make use of RNAse polymerase-III, such as Epstein Barr virus, adenovirus, vesicular stomatitis virus en rabies virus.

Antinuclear antibodies are not induced by PUVA treatment in patients with uncomplicated psoriasis

BACKGROUND

Previous investigations of antinuclear antibody (ANA) prevalence in patients undergoing PUVA therapy reported contrasting results. However, ANA tests were performed on low-sensitivity substrates that do not allow investigation of anti-Ro (SS-A) antibodies.

OBJECTIVE

We assessed ANAs on a highly sensitive substrate.

METHODS

ANAs were assayed on HEp-2 cells at regular intervals in 238 patients with psoriasis who were treated with PUVA therapy for 1 to 5 years and in 118 untreated control subjects with psoriasis. In addition, radioimmunoassay and counterimmunoelectrophoresis studies of anti-DNA and anti-extractable nuclear antigen antibodies were performed.

RESULTS

Low titers of ANA developed in three patients in at least two consecutive determinations and in 10 patients in a single determination despite continuing treatments. The positive conversion rate was not statistically significant. Radioimmunoassay counterimmunoelectrophoresis studies of anti-DNA and anti-extractable nuclear antigen antibodies were never positive.

CONCLUSION

In our experience PUVA therapy does not represent a risk factor for the induction of anti-Ro antibodies and other ANAs.

Cell membrane, a target for PUVA therapy

The photochemical reactions occurring in the cell membranes, sensitized photo-oxidation and psoralen photoaddition to lipids, are briefly reviewed. Phospholipid dynamics in the membrane structure, based on erythrocyte lipid organization, are described. Evidence for alterations of cell membrane functions under psoralen plus UVA radiation (PUVA) treatment in a variety of mammalian cells is presented. Cell receptor dysfunctions under PUVA treatment are demonstrated in a number of biological investigations. The purpose of this survey is to illustrate the feasibility of studying psoralen photobiology with phospholipids. The reaction of psoralens with phospholipids is considered to be one of the triggering mechanisms of the subsequent physiological responses, which may be relevant to PUVA photochemotherapy.

Molecular characterization of the Ro/SS-A autoantigens

Molecular techniques have recently revealed that there are several immunologically distinct Ro/SS-A antigens. Three genes encoding putative Ro/SS-A protein antigens with calculated masses of 46, 52, and 60 kD have been isolated. The encoded amino acid sequence of each is quite dissimilar. The 46-kD antigen is calreticulin (CR), a highly conserved calcium-binding protein that resides predominately in the endoplasmic reticulum where it may be involved in protein assembly. Although CR has recently been confirmed to be a new human rheumatic disease-associated autoantigen, its relationship to the other components of the Ro/SS-A ribonucleoprotein has become somewhat controversial owing predominately to the fact that recombinant forms of calreticulin have not displayed the same pattern of autoantibody reactivity possessed by the native form of this protein. The 52-kD antigen most likely resides in the nucleus and may be involved in the regulation of gene expression. The cellular location and function of the 60-kD antigen is uncertain but studies indicate that it is a RNA-binding protein. The 46- and 60-kD antigens share homology with foreign polypeptides, suggesting that an immune response initially directed against a foreign protein may give rise to the autoimmune response directed at cross-reacting self proteins.

Increased oxidative metabolism in phytohemagglutinin-stimulated lymphocytes from patients with systemic lupus erythematosus is associated with serum SSA antibody

We have examined oxidative metabolism in phytohemagglutinin (PHA)-stimulated lymphocytes from patients with systemic lupus erythematosus (SLE) because increased oxygen free radicals would explain the DNA abnormality previously observed in these cells. Almost no oxidative activity was found in freshly isolated control or lupus lymphocytes or control lymphocytes stimulated with PHA. However, increased oxidative metabolism, measured by nitroblue tetrazolium (NBT) conversion to formazan, was found in PHA-stimulated lymphocytes from 14 of 21 lupus patients. A time course study showed that NBT activity appeared in positive lupus lymphocytes at 1-2 days of PHA stimulation, increased to a maximum at 2-4 days, and diminished thereafter. NBT activity was not related to specific disease symptoms, drug therapy, or serum dsDNA, Sm, RNP, or SSB (La) antibodies. The selected population of lupus patients studied precluded conclusions about NBT activity and disease severity. However, the intensity of NBT response in stimulated lupus lymphocytes was positively correlated with the presence of serum SSA (Ro) antibody. We suggest that increased oxidative activity of SLE lymphocytes generates a chemical change in endogenous DNA in vivo and may be a primary event in the pathogenesis of autoimmunity. Absence of detectable oxidative activity in stimulated lymphocytes in a subgroup of lupus patients suggests that at least two different mechanisms are associated with the altered DNA profiles observed in this disorder.