The glycosylphosphatidylinositol-anchored membrane protein CD24 functions as an adhesion molecule for P-selectin and L1 and plays a role in B-cell development and neurogenesis. Over the last few years, a large body of literature has also implicated CD24 expression in tumorigenesis and progression. Here, we show that ectopic CD24 expression can be sufficient to promote tumor metastasis in experimental animals. By developing a doxycycline-inducible system for the expression of CD24 in breast cancer cells, we have also analyzed the cellular properties that CD24 expression influences. We found that CD24 expression increased tumor cell proliferation. Furthermore, in addition to promoting binding to P-selectin, CD24 expression also indirectly stimulated cell adhesion to fibronectin, collagens I and IV, and laminin through the activation of A 3 B 1 and A 4 B 1 integrin activity. Moreover, CD24 expression supported rapid cell spreading and strongly induced cell motility and invasion. CD24-induced proliferation and motility were integrin independent. Together, these observations implicate CD24 in the regulation of multiple cell properties of direct relevance to tumor growth and metastasis. (Cancer Res 2005; 65(23): 10783-93)

Long term B lineage chimeras are used here to study the origin of plasma cells in the mouse. Chimeric mice are constructed by reconstituting lethally irradiated mice with peritoneal cells (PerC) and bone marrow cells from congenic pairs of mice differing in Igh-C allotype. All conventional B cells in these mice express the allotype of the bone marrow donor and nearly all Ly-1 B lineage cells express the allotype of the PerC donor. FACS analysis and immunohistology of these mice shows that virtually all (sig+) B cells in peripheral lymphoid organs are derived from the bone marrow donor. However, despite this overwhelming number of bone marrow-derived B cells in these animals, immunohistological staining of lymphoid organs and gut shows that nearly half of the IgM, IgG, and IgA plasma cells derive from the PerC donor. These data demonstrate that the peritoneal cavity contains a major reservoir of self-replenishing cells that play a significant role in the mucosal immune response. The possibility that these are B cells that belong to the Ly-1 B lineage is discussed.

Mammalian hibernation consists of torpor phases when metabolism is severely depressed, and T(b) can reach as low as approximately -2°C, interrupted by euthermic arousal phases. Hibernation affects the function of the innate and the adaptive immune systems. Torpor drastically reduces numbers of all types of circulating leukocytes. In addition, other changes have been noted, such as lower complement levels, diminished response to LPS, phagocytotic capacity, cytokine production, lymphocyte proliferation, and antibody production. Hibernation may therefore increase infection risk, as illustrated by the currently emerging WNS in hibernating bats. Unraveling the pathways that result in reduced immune function during hibernation will enhance our understanding of immunologic responses during extreme physiological changes in mammals.

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