A novel urinary sialoglycoprotein as the inhibitor of interleukin-1

An inhibitor of interleukin-1 (IL-1) was purified to homogeneity from febrile human urine by using a sequence of ammonium sulphate fractionation, DEAE-cellulose chromatography and gel filtration on a column of ACA 54. The inhibitor was a sialoglycoprotein and its molecular weight, examined by SDS-PAGE, was found to be 30 kD. It was acidic in nature and its isoelectric point, determined by electrofocusing on thin-layer polyacrylamide gels, was found to be 3.5-3.6. The inhibitor was sensitive to the action of sialidase from Vibrio cholerae as the enzyme treated material was electrofocused at a higher pH range (4.5-5.2). The inhibitor contained 10% sialic acid as estimated by the Thiobarbituric acid assay. It interacted with the lectins jacalin and concanavalin A, suggesting the presence of carbohydrate moieties such as galactose and mannose. The inhibitor did not block the specific binding of IL-1 to cells, nor did it directly bind IL-1. Early rejection urine from a kidney transplant patient was also found to contain the 30 kD IL-1 inhibitor protein. This was visualised by immunoblotting using specific antibody raised against the 30 kD IL-1 inhibitor isolated from the urine of febrile patients.