Monoclonal antibodies to human recombinant interleukin 1 (IL 1)beta: quantitation of IL 1 beta and inhibition of biological activity.

ABSTRACT

Monoclonal antibodies (McAb) were developed to the Mr 17,500 form of human recombinant interleukin 1, IL 1 beta. Four McAb have been identified that inhibit the biological activity of IL 1 beta. McAb H34 and H67, at 1 microgram/ml (6 X 10(-9) M), completely inhibit the capacity of 1 ng/ml (6 X 10(-11) M) recombinant IL 1 beta to stimulate the proliferation of murine thymocytes or human fibroblasts in vitro. McAb H6 and H21 are approximately 10-fold less potent, and completely inhibit IL 1 beta activity at 10 micrograms/ml (6 X 10(-8) M) in both assays. The McAb do not have a significant effect on the biological activity of human recombinant IL 1 alpha in either assay. These McAb block the binding of recombinant [125I]IL 1 beta to IL 1 receptors on mouse 3T3 fibroblasts and have affinity constants for IL 1 beta in the range of 10(9) to 10(10) liters/mol. Competition studies suggest that two nonoverlapping epitopes on the IL 1 beta molecule are recognized by the McAb. H6 and H34 recognize one epitope, and H21 and H67 another. McAb H6 and H67 have been used together in a two-site ELISA to detect IL 1 beta. The sensitivity of the ELISA, which is 15 pg/ml (0.86 pM), approaches the limit of sensitivity of the thymocyte proliferation assay. The ELISA and thymocyte proliferation assay were used to quantitate IL 1 beta in E. coli LPS-stimulated human monocyte culture supernatants (HMCS). The level of IL 1 beta detected by ELISA in culture supernatants from eight donors ranged from 1.7 to 5.6 ng/ml, with a mean value of approximately 3 ng/ml. By comparison, the thymocyte proliferation assay gave levels of IL 1 in HMCS that were eight fold higher when quantitated by using recombinant IL 1 beta as a standard. This discrepancy with the bioassay used was reflected by the three fold higher maximum stimulation of thymocyte proliferation by HMCS as compared with recombinant IL 1 alpha or IL 1 beta, and only 45% inhibition of HMCS IL 1 activity by McAb. Thus, factors other than IL 1 beta account for the IL 1-like activity in monocyte culture supernatant as measured by the bioassay. The ILB1 McAb and ELISA allow for the first time-sensitive, accurate, and convenient quantitation of IL 1 beta levels in biological fluids or specimens.