Frequency of B cells expressing germ-line γ1 transcripts upon IL-4 induction

Murine B cells when activated with LPS and IL-4 have been shown to secrete IgG1 and IgE with corresponding H chain gene rearrangements. Using this system it has been previously demonstrated that transcription of γ1 and ∈ C region genes in their germ-line configuration occurs before switch recombination. Here, for the first time, the frequencies of B cells expressing germ-line γ1 transcripts are analyzed using in situ hybridization methodology. The results indicate that the combination of LPS and IL-4 induces a relatively low frequency of cells (5-12%) to express germ-line γ1 transcripts. Germ-line γ1 transcript- expressing cells were first detected on day 1 of culture with LPS and IL-4 and reached a maximum by days 3 to 5. The B cells that expressed germ-line γ1 transcripts appeared to be activated based on size and morphology. The frequency of B cells expressing germ-line γ1 transcripts approximated the frequency of Cγ1⁺ plasma cells that appeared later in the cultures. These data may suggest a correlation between germ-line Ig transcript expression and the frequency of B cell precursors committed to the expression of a particular isotype.