Unique T cell Ia antigen expressed on a hybrid cell line producing antigen-specific augmenting T cell factor

Hybrid cell lines were established by fusion between keyhole limpet hemocyanin(KLH) binding T cells of A/J mice and an AKR T cell tumor line, BW5147. Hybrids were selected for the presence of Ia antigen and KLH-specific augmenting activity of their extracts in the secondary antibody response. The detailed phenotypic and functional analysis of 1 of these clones, FL10, is reported here. The hybrid was positive for both Thy1.1 and Thy1.2 antigens and possessed the Lyt-1+,2-,3- phenotype. Both VH and Ia determinants were detected on their cell surface. The IA locus was mapped in the I-A subregion, but the Ia specificities were serologically distinct from those of B cell Ia antigen. This was demonstrated by the fact that anti-Ia antiserum preabsorbed with B cells could react with the hybrid cells, whereas none of the monoclonal anti-Ia specific for private and public determinations of Iak could. The extract from the cell line specifically augmented the in vitro secondary antibody response against dinitrophenylated KLH, and this activity was removed by absorption with antigen and conventional anti-Ia antisera. The results indicate that the cell line, FL10, carries Ia antigen unique to the T cell, which is associated with the antigen-specific augmenting molecule.