Social Efficiency of Entry in an Open Economy

We show that cost asymmetry between the domestic and foreign firms is not necessary for the occurrence of insufficient entry in the domestic country. This result provides a rationale for pro-competitive domestic policies even in the absence of cost asymmetries among the domestic and foreign firms. However, if significant demand comes from foreign countries, and the market structures are determined endogenously in the domestic and foreign countries, domestic-entry in an open economy might not be insufficient, implying that foreign competition might not reduce the importance of anti-competitive domestic policies.

Two Rationales for Insufficient Entry

This study offers two new rationales for insufficient entry in a given industry. The first is the presence of complementary industries. Suppose there is free entry in an industry and the complementary industries are monopolistic. If the number of complementary industries is sufficiently high, then there is insufficient entry. However, if these industries are substitutes, then there is always excessive entry. The second rationale is that there is cost-reducing R&D investment and spillover. When the spillover rate is sufficiently high, there is insufficient entry. Further, we consider the general model and obtain similar results.

Price-Dependent Demand in Spatial Models

This paper introduces price-dependent individual demand into the circular city model of product differentiation. We show that for any finite number of firms, an unique symmetric price equilibrium exists provided that demand functions are not “too” convex. As in the case of unit demand, the number of firms under free entry decreases in the fixed cost of entry while increases in the transportation cost of consumers. However, this number is no longer always in excess of the socially optimal level. Insufficient entry occurs when the fixed and transportation costs are high.

Entry Regulation under Asymmetric Information about Demand

We investigate how an incumbent firm can use the regulatory policy about entry and the informational advantage to protect his market position. This question is studied through the construction of a signalling game where we assume that the regulator has less information about demand than the firms. We conclude that there is a pooling equilibrium and partially separating equilibria in which entry is deterred and, if demand is high, there will be insufficient entry. The final effect on welfare depends on the tradeoff between short-run benefits (lower price) and long-run losses (weaker competition).

Intrathymic transplantation of bone marrow–derived progenitors provides long-term thymopoiesis

The sustained differentiation of T cells in the thymus cannot be maintained by resident intrathymic (IT) precursors and requires that progenitors be replenished from the bone marrow (BM). In patients with severe combined immunodeficiency (SCID) treated by hematopoietic stem cell transplantation, late T-cell differentiation defects are thought to be due to an insufficient entry of donor BM progenitors into the thymus. Indeed, we find that the intravenous injection of BM progenitors into nonconditioned ζ-chain–associated protein kinase 70 (ZAP-70)–deficient mice with SCID supports short- but not long-term thymopoiesis. Remarkably, we now show that the IT administration of these progenitors produces a significant level of donor-derived thymopoiesis for more than 6 months after transplantation. In contrast to physiologic thymopoiesis, long-term donor thymopoiesis was not due to the continued recruitment of progenitors from the BM. Rather, IT transplantation resulted in the unique generation of a large population of early c-Kithigh donor precursors within the thymus. These ZAP-70–deficient mice that received an IT transplant had a significantly increased prothymocyte niche compared with their untreated counterparts; this phenotype was associated with the generation of a medulla. Thus, IT administration of BM progenitors results in the filling of an expanded precursor niche and may represent a strategy for enhancing T-cell differentiation in patients with SCID.