Identification of a murine monoclonal antibody specific for an allotypic determinant on mouse CD3

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Abstract
A murine monoclonal antibody (mAb; 7D6) that was mitogenic for T cells was derived from 129/Sv animals immunized with a T helper clone from C57BL/6 origin. Fluoresceinated 7D6 labeled T cells from most common mouse strains but not from 129/Sv and LP/J animals, and this labeling was inhibited by the anti-CD3 ϵ mAb 145-2C11. The mitogenicity of 7D6 for T cells had a similar strain specificity. The antibody immunoprecipitated the T cell receptor (TcR) complex from a T cell hybridoma. After dissociation of this immunoprecipitate with detergents, the CD3 γ and ϵ chains were retained by the 7D6 antibody. Immunoprecipitation data were also obtained with COS cells transfected with the CD3 γ, δ or ϵ chains alone, in pairs or together. They confirmed that 7D6 bound the CD3 γϵ pair, suggesting that the antibody recognizes a conformational epitope formed by γϵ pairing, whereas 145-2C11 bound both γϵ and δϵ pairs. These results, therefore, add to current information about TcR structure and subunit stoichiometry. We have demonstrated that the 7D6 mAb specifically binds to a CD3 dimer comprised of γ and ϵ chains. We thus provide additional evidence that indicates that two CD3 ϵ chains are found within the receptor, one linked to CD3 γ and the other to CD3 δ.