Quorum sensing contributes to activated IgM-secreting B cell homeostasis.

Maintenance of plasma IgM levels is critical for immune system function and homeostasis in humans and mice. However, the mechanisms that control homeostasis of the activated IgM-secreting B cells are unknown. After adoptive transfer into immune-deficient hosts, B lymphocytes expand poorly, but fully reconstitute the pool of natural IgM-secreting cells and circulating IgM levels.

Positive selection of B cells expressing low densities of self-reactive BCRs.

B cell tolerance or autoimmunity is determined by selective events. Negative selection of self-reactive B cells is well documented and proven. In contrast, positive selection of conventional B cells is yet to be firmly established.

B-cell homeostasis, competition, resources, and positive selection by self-antigens.

In adult mice, the number of B lymphocytes remains constant under homeostatic control, in spite of the fact that B cells are produced continuously in numbers that largely exceed the number required to replenish the peripheral pools. It follows that each newly formed lymphocyte can only persist if another lymphocyte dies. In an immune system where the total number of cells is limited, cell survival is no longer a passive phenomenon but rather a continuous active process where each lymphocyte must compete with other lymphocytes to survive.