A NEW ELISA FOR THE DETECTION OF ANTI-HEPARAN SULFATE REACTIVITY, USING PHOTOBIOTINYLATED ANTIGEN

Autoantibodies reacting with a great variety of autoantigens are chara cteristic for the autoimmune disease systemic lupus erythematosus (SLE ). Although reactivity with heparan sulfate (HS) in sera of patients w ith SLE is found in association with the occurrence of nephritis, the aetiological significance of this association is not clear. The assay which is generally used to measure anti-HS reactivity is subject to fa lse-positive results, as a consequence of the binding of negatively ch arged moieties within immune complexes to the precoat employed (protam ine sulfate). Therefore, we have developed a new ELISA in which photob iotinylated HS is efficiently and reproducibly bound to streptavidin-c oated wells. We compared the new ELISA with the classical anti-HS ELIS A by testing culture supernatants of 20 murine monoclonal antibodies ( mAb) to DNA (containing free anti-DNA and anti-DNA/nucleosome immune c omplexes) and preparations of these mAb (containing only free anti-DNA ), purified under dissociating conditions. In the classical anti-HS EL ISA, 14 out of 20 of the culture supernatants reacted positively with HS; after purification no reactivity remained. The discrepancy must be due to anti-DNA/nucleosome immune complexes present in the culture su pernatants. In the new ELISA only four out of 20 culture supernatants and one of the purified preparations reacted with HS. This latter reac tivity is probably not specific, since this mAb also reacted with stre ptavidin alone. To find out whether there is a correlation between the occurrence of nephritis and anti-HS reactivity, measured in this new anti-HS ELISA, we tested sera of patients with a renal- or non-renal e xacerbation of SLE in the newly developed anti-HS ELISA. We observed a correlation between anti-HS reactivity and nephritis.