Characterization of a monoclonal antibody with CD44 like reactivity

QE7.3E8 is a monoclonal antibody which precipitates two bands (90 and 160 kd) from a B cell line and four (90, 130, 146, and 160 kd) from monocytes. Whilst this immunoprecipitation pattern suggests that QE7.3E8 is a CD18 antibody, a number of other results are inconsistent with this interpretation. In particular, QE7.3E8 stains lymphoid tissue with a distribution clearly distinguishable from CD18 antibodies; it precipitates four bands from a T cell line which does not express the CD11b and CD11c alpha chains, and cross immunoprecipitation with QE7.3E8 and a CD11a antibody show that the molecules recognized by these antibodies are not associated. However, in tissue distribution and sequential precipitation experiments QE7.3E8 behaves like a CD44 antibody. CD44 identifies a single 85 kd protein, but high molecular weight complexes have been described, accounting for the multiple bands seen in immunoprecipitation studies. Sequential immunoprecipitation using QE7.3E8 and a Workshop-clustered monoclonal antibody (SBU 25-32) indicate that the QE7.3E8 reacts with the CD44 antigen.