Correlation of presentation of insulin with surface I-Ad and A alpha and A beta mRNA expression by cloned B lymphoma hybridoma variants

We investigated the relationship between Ia expression and antigen presentation in cloned B cells, using variants of TA3 antigen presenting cells. Two TA3 subclones were selected as high presenters and 5 as low presenters of insulin to pork insulin/I-Ad restricted T cells. All TA3 subclones express the surface I-Ak, I-Ek, I-Ad and I-Ed Ia antigens characteristic of the parental cell line. However, surface I-Ad levels correlated best with the ability to present insulin, since high presenters express 2- to 4-fold more I-Ad than low presenters. High presenters possess 2- to 4-times more A alpha and A beta Ia mRNA than low presenters and also transcribe these mRNAs 2- to 5-fold faster than most low presenters. Thus, the correlation noted between I-Ad surface density and capacity to present insulin by our panel of TA3 variants is regulated at the level of transcription and not translation of I-Ad specific mRNAs.