In this issue of Cell, Schindler et al. (2006) show that the Nef protein from nonpathogenic strains of simian immunodeficiency virus (SIV) induces the downregulation of host T cell receptor/CD3, whereas Nef from human immunodeficiency virus (HIV-1) does not. This loss of function in the Nef of HIV-1 may partly explain the pathogenicity of this virus.

Arvind Panagariya Analytically as well as politically, migration is a more complex phenomenon than international trade. The latter involves two-way flows of goods and services that allow the real aggregate income to grow in each country involved. Therefore, the arguments for protection against imports typically rest on the detrimental effects on the income distribution or the existence of prior...