Thymocytes as well as mature Band T-cells PiB derived from the spleen of the VLV or VV mice did not show any difference in survival in culture when compared to those ones derived from wt mice. Unexpectedly, the 5α-Androstane-3α,17β-diol Bcells derived from the lymph nodes of VLV mice appeared more resistant to spontaneous apoptosis than the ones of VV or wt mice that died with similar kinetics. Together our results show that Venus expression is well tolerated in lymphocytes over time in vivo. Also, in the VLV strain chosen for detailed analysis, transgene insertion may influence expression/function of gene associated with the survival of mature B cell, at least in vitro. However, since we did not observe B cell accumulation in vivo this observation was not followed up in detail. We continued our analysis quantifying the percentage of Venus + cells in different primary and secondary lymphatic organs. Therefore, we stained single cell suspensions with antibodies specific for different cell surface markers, identifying T-cells, Bcells or myelocytes and performed flow cytometric analysis. Venus + cells were found in all the leukocyte subpopulations tested. However, the relative percentage of Venus + cells varied between the individual transgenic lines as well as between littermates, indicating variegated expression of the reporter or mosaicism due to stochastic gene silencing. Similar observations were made in all other lymphoid organs analyzed. In VLV transgenic mice, T cells showed Venus expression in all the organs ranging from 35%�C80%, with highest expression found in CD8 + T cells in lymph nodes and spleen, while the percentage of Venus + CD4 + T cells was frequently lower in thymus, peripheral blood, spleen, lymph node and bone marrow. In the CD19 + B cell compartment in the periphery, we found that transgene expression was actually highly comparable between spleen, peripheral blood and bone marrow with 70�C80% of Venus expressing B cells, but only about half of the B cells in the lymph node were expressing the transgene. Immature pro- and pre-B-cells in the bone marrow also expressed Venus, with a slightly higher percentage of transgene positive pro-B than pre-B cells. The percentage of Venus + Mac1 + myelocytes was comparable to the percentage of Venus lymphocytes in the spleen, while it was significantly lower in the bone marrow and peripheral blood of VLV mice.