Monoclonal antibodies reacting with the interleukin 1 receptor define a multi‐molecular complex

By sequential immunization with a variety of different interleukin (IL) 1 receptor (IL 1R)-bearing cells and by generating a large number of clones from a single fusion experiment, we have managed to produce two monoclonal antibodies which react with the lymphocyte IL 1R. The antibodies also react with the mouse fibroblast line, 3T3, but we have not yet defined their reactivity with cells carrying low-affinity receptors. Immunoprecipitation allows the IL 1R to be isolated from EL4 6.1 cell membrane preparations and shows that the IL 1R exists as a complex. The antibodies clearly interfere with IL 1 responses both in vitro and in vivo. These are the first anti-mouse IL 1R antibodies to be described which clearly and profoundly affect the immune response.