Phenomenon of human T cells rosetting with sheep erythrocytes analyzed with monoclonal antibodies. "Modulation" of a partially hidden epitope determining the conditions of interaction between T cells and erythrocytes

Abstract

Anti-D66 is a monoclonal antibody able to inhibit sheep erythrocyte(E)-rosette formation of T cells both at 4.degree. C and at 37.degree. C, but that does not inhibit T cell rosette formation with neuraminidase or 2-amino-ethylisothiouronium bromide(AET)-pretreated E (EAET). As demonstrated by capping experiments, it defines an epitope, D66, that is directly involved in E-rosette formation. D66 is distinct from the epitope defined by 9.6 because 9.6, a previously defined pan-T monoclonal antibody, inhibits EAET rosette formation and because no cross-blocking occurred. 9.6 and D66 are carried by the same molecule, as demonstrated by sequential immunoprecipitation assays performed on 2 different T cell lines. On the thymocyte surface 9.6 and D66 are most probably carried by the same molecule, as indicated by cocapping and colysostripping experiments. D66 is present at higher densities on thymocytes and activated T cells than on peripheral blood T cells. Investigation of numerous T cell populations, both normal and malignant, showed a straightforward correlation between elevated D66 density and ability to form 37.degree. C stable E-rosettes. Neuraminidase treatment of thymocytes and peripheral blood lymphocytes forming E-rosettes unmasked a large fraction of D66 not readily accessible on their surface. These hidden D66 epitopes appear to be responsible for a surprising observation: the ability of anti-D66 to inhibit E-rosette formation could be totally reversed by fixation on anti-D66 of an antibody to mouse Ig or an Fab fragment anti-mouse Ig. This would induce microdisplacement with emergence of hidden D66, as documented by fluorometric studies. Malignant T cells with a differentiative status of mature T cells, but forming no (or low numbers of) E-rosettes, could be induced to display D66 and to form E-rosettes by neuraminidase treatment.