High expression of cloned immunoglobulin kappa gene in transgenic mice is restricted to B lymphocytes.

Immunoglobulin genes are normally expressed only in cells of the B lymphocyte lineage after a variable (V) and constant (C) gene rearrangement has occurred. To study the control of immunoglobulin gene expression in a defined situation, we have produced transgenic mice by microinjecting a rearranged mouse immunoglobulin kappa gene (designated pB1-14) into fertilized mouse eggs. We present here the analysis of six different kappa-transgenic mouse lines. All the transgenic mice express the microinjected kappa gene in a completely tissue-specific fashion. Transcripts from pB1-14 are found at a high level in the spleen, but are undetectable in nonlymphoid tissues of testis, liver, kidney, heart, muscle, brain and thyroid gland. In lymphoid cell subpopulations, the level of pB1-14 transcripts is correlated with the relative number of B cells; there is no correlation with the proportion of T lymphocytes. We concluded, therefore, that the microinjected kappa gene contains target sequences for B lymphocyte-specific gene activation signals that override the influence of the integration site.