PRESENTATION OF ANTIGEN BY MIXED ISOTYPE CLASS-II MOLECULES IN NORMAL H-2D MICE

A panel of DBA/2 T cell hybridomas specific for the sperm whale myoglobin epitope 110-121 was found to recognize antigen presented by the mixed isotype class II molecule E-alpha(d)A-beta(d). The response was blocked by monoclonal antibodies specific for E-alpha and A-beta(d) chains; in addition, the hybridomas responded to antigen presented by L cells expressing E-alpha(A)beta(d) molecules, and made no response with L cells expressing I-A(d) or I-E(d) molecules. Two more groups of hybridomas isolated from DBA/2 and B10.D2 mice immunized with myoglobin also recognized peptide 110-121 presented by E-alpha(d)A-beta(d). Thus, although it is expressed at biochemically undetectable levels on spleen cells, the E-alpha(d)A-beta(d) molecule is an important presenting element in normal H-2d mice making a conventional immune response to a protein antigen. These results suggest that high levels of class II expression are not a prerequisite for T cell activation.