Accelerated emigration of B lymphocytes in the Xid mouse

The B cell receptor is required for the emigration of newly generated B lym phocytes and for their maintenance in the periphery, A specific maintenance defect was noted in fraction I (IgD(high)lgM(low)) B cells in Sid mice (wh ich harbor a mutation in Btk), Although Bcl-2 levels in fractions I and Il (IgD(high)IgM(high)) are equivalent in normal and Xid B cells, a novel peak of Bcl-2(low) fraction III (IgD(low)IgM(high)) B cells was noted in the Xi d mouse. Since this B cell population resembled bone marrow immature B cell s,,ve examined the emigration of newly formed B cells in normal and Xid mic e. These studies revealed the accelerated emigration of newly formed Xid B cells. We conclude that distinct Btk-independent and Btk-dependent signals mediate emigration and maintenance events during peripheral B cell maturati on.