Figure 4.

Detection of I promoter–generated post-switch (circle) transcripts in stimulated 3H9sdVk8sd scid spleen cells. PCR-amplified Iγ3-Cμ, Iγ1-Cμ, Iγ2b-Cμ, and Iα-Cμ transcripts in cDNA from 2-d cell cultures stimulated with LPS, LPS/IL4, and LPS/TGFβ, respectively, were readily detectable by Southern blot analysis of gel-separated PCR products. The transcripts are seen in the plus (+) lane for each genotype of mouse tested: nontransgenic scid/+ (s/+), 3H9sdVκ8 scid/+ (tg s/+), and 3H9sdVκ8sd scid (tg s/s). Post-switch circle transcripts were not detectable in nonstimulated cells taken directly from the animal (minus [−] lanes; except for the barely detectable Iγ3-Cμ transcripts in the s/+ controls). β2M, visualized by ethidium bromide staining of the gel, served as an internal control for cDNA input.