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

Abstract

The CH12 B cell lymphoma can be stimulated to secrete antibody by helper T cells that interact with I-E^K but not I-A^K 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_α and A_β 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_α or A_β which could account for these observations. The implications of these findings on the role of class II molecules in B cell activation is discussed.