URINARY LOSS OF IMMUNOGLOBULIN-G ANTI-F(AB')(2) AND ANTI-DNA ANTIBODYIN SYSTEMIC LUPUS-ERYTHEMATOSUS NEPHRITIS

The objective of this study was to determine whether the low levels of serum immunoglobulin G (IgG) anti-f(ab')(2) seen in some patients wit h active systemic lupus erythematosus (SLE) were directly related to t he deposition of antibody with this specificity in the kidney or alter natively td the urinary loss of IgG anti-f(ab')(2). Serum Levels of Ig G anti-f(ab')(2), anti-tetanus toroid, and anti-ds DNA antibody were m easured in parallel with urinary excretion of these same 3 antibodies in 28 patients with SLE nephritis and in 28 control patients with othe r forms of chronic kidney disease. Low levels of both serum IgG anti-f (ab')(2) or anti-tetanus antibody appeared to correlate with increased levels of urinary loss of these same antibodies in some patients with SLE and in control subjects with kidney disease. However, urinary los s could not account for low serum levels of either IgG antibody in man y subjects. Quantitative 24-hour urinary losses of IgG anti-f(ab')(2) and anti-DNA were much higher in patients with SLE than in control sub jects with kidney disease (P < .05), whereas amounts of IgG urinary lo ss of anti-tetanus were similar in patients with SLE and in control su bjects. In nearly 1 third of SLE nephritis patients, 13% to 53% of tot al excreted urinary IgG showed anti-DNA enzyme-linked-immunosorbent as say reactivity. Urinary IgG in many patients with SLE showed both anti -DNA and anti-f(ab')(2) reactivity, but dual anti-DNA/F(ab')(2) specif icity was more pronounced in affinity-isolated serum IgG anti-DNA or a nti-f(ab')(2) than in excreted urinary IgG molecules. The affinity of urinary IgG for either DNA or F(ab')2 was much lower than the same ant ibody activities measured either in serum or in kidney biopsy eluates. When the relative affinity of anti-DNA antibody in serum, urine, and kidney biopsy eluate was measured in parallel, the highest affinity an tibody was found in kidney biopsy eluates, followed by serum antibody with urine antibody affinity showing the lowest values. These findings suggest a relative concentration of the highest affinity doubly react ive IgG anti-DNA/F(ab')(2) in SLE kidney tissues during SLE nephritis and implicate this process as an important factor in ongoing tissue da mage.