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Many survival pathways influence B cell lifespan, yet how survival is regulated throughout B cell development is not fully understood. Non-engaged BCRs are thought to induce tonic signals critical for B cell survival and development. Cytokines are also known to influence B cell survival at many stages of development. It has been reported that a fraction of immature bone marrow B cells bind BAFF, a known B cell survival factor. Using 3-83Igi knock-in mice we are investigating the relationship between BCR and cytokine receptor signaling in immature B cell survival. We hypothesize that tonic signaling through non-autoreactive BCRs leads to the expression of BAFF-R on immature B cells, and the combination of survival signals through these receptors permits their further development and entry into the periphery. While we observe a positive correlation between the level of non-autoreactive BCR and BAFF-R expression on the surface of immature B cells, we are yet to find evidence that BAFF-R plays a functional role in the survival of B cells at this stage. However our data support the hypothesis that a threshold level of tonic BCR signal is required for B cell development, and suggests that the intensity of tonic BCR signals may be important for both the differentiation and survival of developing B cells. [ABSTRACT FROM AUTHOR]