The lymphoid organs contain specialized microanatomic structures composed of lymphoid, myeloid and stromal cells that are vital to the generation of an effective adaptive immune response. Although the existence of these specialized structures has been known for over a century, the developmental signals that generate them and the specific roles of these structures in the immune response have remained largely elusive. Because of their position adjacent to the marginal sinuses, marginal zone B (MZB) cells are amongst the first population of cells seen by blood born antigens and are presumed to have a critical role in host defense against bacterial pathogens. Here we demonstrate that a deficiency of the tyrosine kinase (Pyk-2) results in a cell autonomous defect of MZB cell production. In response to repetitive polysaccharide antigens (T-independent type II (TI-II)) Pyk-2-deficient mice displayed marked suppression of IgM, IgG3 and IgG2a production. Furthermore, complement receptor engagement proved necessary for the specific targeting of polysaccharide antigens to MZB cells. These results suggest how innate immune responses mediated through complement coupling are translated into an adaptive response by MZB cells, and provide a potential mechanism for the T cell independence of humoral responses to polysaccharide antigens.

No abstract

The biological role of the protein tyrosine kinase, Pyk2, was explored by targeting the Pyk2 gene by homologous recombination. Pyk2؊͞؊ mice are viable and fertile, without overt impairment in development or behavior. However, the morphology and behavior of Pyk2؊͞؊ macrophages were impaired. Macrophages isolated from mutant mice failed to become polarized, to undergo membrane ruffling, and to migrate in response to chemokine stimulation. Moreover, the contractile activity in the lamellipodia of Pyk2؊͞؊ macrophages was impaired, as revealed by measuring the rearward movement toward the nucleus of fibronectin-coated beads on the lamellipodia in opposition to an immobilizing force generated by optical tweezers. Consistently, the infiltration of macrophages into a carageenan-induced inflammatory region was strongly inhibited in Pyk2؊͞؊ mice. In addition, chemokine stimulation of inositol (1, 4, 5) triphosphate production and Ca 2؉ release, as well as integrin-induced activation of Rho and phosphatidyl inositol 3 kinase, were compromised in Pyk2؊͞؊ macrophages. These experiments reveal a role for Pyk2 in cell signaling in macrophages essential for cell migration and function.

Abstract-We investigated whether the mobilization of endothelial progenitor cells (EPCs) by exogenous erythropoietin (Epo) promotes the repair of injured endothelium. Recombinant human Epo was injected (1000 IU/kg for the initial 3 days) after wire injury of the femoral artery of mice. Neointimal formation was inhibited by Epo to 48% of the control (PϽ0.05) in an NO-dependent manner. Epo induced a 1.4-fold increase in reendothelialized area of day 14 denuded vessels, 55% of which was derived from bone marrow (BM) cells. Epo increased the circulating Sca-1 ϩ /Flk-1 ϩ EPCs (2.0-fold, PϽ0.05) with endothelial properties NO dependently. BM replacement by GFP-or ␤-galactosidaseoverexpressing cells showed that Epo stimulated both differentiation of BM-derived EPCs and proliferation of resident ECs. BM-derived ECs increased 2.2-to 2.7-fold (PϽ0.05) in the Epo-induced neoendothelium, where the expression of Epo receptor was upregulated. Epo induced Akt/eNOS phosphorylation and NO synthesis on EPCs and exerted an antiapoptotic action on wire-injured arteries. In conclusion, Epo treatment inhibits the neointimal hyperplasia after arterial injury in an NO-dependent manner by acting on the injured vessels and mobilizing EPCs to the neo-endothelium.