Transgenic expression of the γ1 heavy chain gene. (A) T cell–depleted splenocytes from the various transgenic mice were cultured in LPS or LPS+IL-4. Germline transcripts from the endogenous and transgenes were distinguished by a 4-bp insertion resulting in a TaqI restriction site (arrows in schematic). RNA samples were derived from cells cultured in LPS+IL-4. (B) Post-switch transcripts. Expression patterns for germline and post-switch transcripts from B cells from lines 234Δ and 234 were identical to those from lines 820Δ and 820 (not depicted). (C) HPRT mRNA expression. (D) µ-γ1 CSR, distinguishing the transgene and endogenous genes, was tested by DC-PCR. Note that the 231Δ sample has a larger amount of fragment from the endogenous genes. (E) The same amount of 820Δ LPS+IL-4 and 820 LPS+IL-4 tested in Part B, and three fivefold dilutions of the 820 cDNA, were tested for transgenic VDJCγ1 expression. Each experiment shown was repeated in one or two additional experiments. Black lines between lanes indicate that the order of the lanes has been rearranged from the original electronic file, or that the lanes are derived from an independent experiment.