Comparative sequence analysis of cDNA clones encoding I-A molecules of the CH12 B cell lymphoma: nucleotide differences do not account for their "defective" function in B cell stimulation.

The CH12 B cell lymphoma can be stimulated to secrete antibody by helper T cells that interact with I-EK but not I-AK molecules expressed on its membrane. Both molecules present antigen to the appropriate T cells. We have analyzed the mRNA by Northern blot analysis and obtained partial sequences of cDNA clones encoding A alpha and A beta of the I-A molecule to determine if deletions or mutations in the cytoplasmic or transmembrane domains account for the "defect" in triggering following interaction with I-A restricted helper T cells. The results provide no evidence for structural alterations in either A alpha or A beta which could account for these observations. The implications of these findings on the role of class II molecules in B cell activation is discussed.