The SmD1 protein is a specific target for the autoantibody response in SLE. To further analyze this reactivity epitope, mapping was performed with cellulose-bound 13-mer peptides overlapping 10 amino acids (aa). In this initial approach, 4 out of 15 SLE sera recognized more than five overlapping peptides of the SmD1 C-terminus. Therefore, longer oligopeptides of up to 37 aa of this region were generated and probed for as antigens by ELISA. For the SmD1 aa 83-119 polypeptide, there was a striking increase of reactivity with 70.0% positive reactions out of 167 SLE sera. In contrast, 105 healthy control sera were negative, and only 8.3% of sera from patients with other inflammatory diseases ( n ϭ 267) exhibited a response, which was of low level only.

Anti-CD4 antibodies have been recently introduced into the therapy of various autoimmune diseases, among them systemic lupus erythematosus (SLE). Their modes of action are not yet fully understood. Interference with cytokine release may be one possible mechanism. Therefore, the effects of anti-CD4 antibodies on the cytokine release of IL-6 (interleukin-6) and TNF-alpha (tumor necrosis factor alpha) were investigated in a whole blood culture system. Basal and phytohemagglutin/lipopolysaccharide (PHA/LPS)-stimulated cytokine patterns were compared to cytokine release after the addition of anti-CD4 antibodies (MAX.16H5) or methylprednisolone in short time whole blood cell culture systems from 12 patients with active SLE, 23 patients with inactive SLE and 12 healthy volunteers. TNF-alpha and IL-6 concentrations were determined in the supernatants by ELISA. High disease activity correlated with an increased production of proinflammatory cytokines. Cell cultures of patients with inactive SLE showed a diminished capacity to respond to mitogenic stimulation. Anti-CD4 antibodies added in vitro suppressed significantly the unstimulated production of IL-6 (P<0.02) in the cell cultures of patients with active SLE and in the PHA/LPS-stimulated cell cultures from both groups of SLE patients (both P<0.001) and healthy volunteers (P<0.01). However, MAX.16H5 did not affect the release of TNF-alpha. In control samples methylprednisolone considerably reduced stimulated and unstimulated IL-6 and TNF-alpha production in all SLE patients, irrespective of the disease state, and in all healthy controls. These data indicate that the proinflammatory cytokines are involved in the pathogenesis of SLE. It is assumed that anti-CD4 antibodies, which can be effective in the treatment of highly active lupus patients, may act via their influence on cytokine release. The decrease of the proinflammatory cytokines IL-6 under therapy with MAX.16H5 could explain the observations of clinical trials and animal studies which showed a reduction of inflammatory parameters and diminished production of autoantibodies following treatment with anti-CD4 antibodies.

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