Development and characterization of two neutralizing monoclonal antibodies to human interleukin-1 alpha

Mice immunized with homogeneous recombinant interleukin-1 alpha (IL-1 alpha) protein developed specific serum titers to the immunogen. Hybridomas resulting from the fusion of the immune spleen or lymph node cells to myeloma cells were analyzed by an antibody capture assay in which the antigen was present in solution. This assay enabled us to isolate two hybridomas secreting antibodies (designated 2F4 and 4G12) that recognized IL-1 alpha and not interleukin-1 beta as judged by the ability of the antibodies to: (a) precipitate IL-1 alpha, (b) inhibit the binding of 125I-IL-1 alpha to the IL-1 receptor on EL4 cells, (c) inhibit the biological activity of IL-1 alpha as measured in a lectin-induced, IL-1-dependent thymocyte proliferation assay. In a double determinant assay configuration, both antibodies, in conjunction with rabbit polyclonal anti-IL-1 alpha antibodies, could detect nanogram concentrations of IL-1 alpha in solution. Cross-inhibition studies indicated that the 2F4 and 4G12 antibodies bind to the same or spatially related epitopes since each can inhibit the binding of the other to IL-1 alpha.