Abstract: The invention relates to novel purified human immunoglobulin E binding factors (IgE-BFs), its individual optionally glycosylated proteins, and fragments thereof, processes for the purification of IgE-BFs, novel monoclonal antibodies to lymphocyte cellular receptors for IgE (Fc.sub..epsilon. R) crossreacting with IgE-Fs, derivatives thereof, processes for the preparation of these antibodies and their derivatives, hybridoma cell lines that produce these antibodies, processes for the preparation of said hybridoma cell lines, the use of the monoclonal antibodies and their derivatives for the qualitative and quantitative determination of IgE-BFs, test kits containing the monoclonal antibodies and/or their derivatives, the use of the monoclonal antibodies for the purification of IgE-BFs, the use of purified IgE-BFs, its individual optionally glycosylated proteins and/or fragments thereof for the prevention and/or treatment of allergy, and to pharmaceutical preparations containing them.