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| - Characterization of defective I-A surface expression in a mixed isotype expressing murine B cell lymphoma: continued expression of EαdAβd despite competition from restored AαdAβd pairs
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| - The BALB/c-derived mouse B cell lymphoma line, 2PK3, expresses mixed Isotype EαdAβd and classical I-E class II molecules on its surface, but normal surface I-A expression is not detectable. Northern blot analysis showed comparable amounts of Aα mRNA In 2PK3 as compared to another lad expressing B cell lymphoma, A20, which predominantly expresses I-A and I-E. Sequence analysis of 2PK3 Aα cDNA revealed a single nucleotide difference in the signal sequence that would result in a proline for leucine substitution at position −12. In vitro translation of 2PK3 Aα mRNA gave results suggesting that the signal peptide mutation prevented translocatlon of the Aα protein across the rough endoplasmic reticulum which would provide an explanation for the lack of I-A expression In 2PK3. I-A expression was restored by transfectlng a functional Aαd gene into 2PK3. Although I-A was expressed at high levels in some transfectants, in all cases significant levels of mixed isotype were still detected. Functional studies performed using antigen-specific l-Ad-restrlcted and Eαb-Aβd-speclfic T cell hybridomas confirmed the levels of expression of I-Ad and EαdAβd respectively on the transfectants and showed that these molecules were functional. An Interesting observation from this study is the continued expression of significant levels of EαdAβd in spite of competition from restored expression of I-Ad.
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