To produce a comprehensive overview of macrophages and related cell types in a short review volume is an impossible task. When I selected the topics to be included, some equally important areas were omitted by necessity, and for this I apologize. My choices have been somewhat eclectic, touching subjects of personal interest (such as osteoclast biology and macrophage electrophysiology) or of current fashion (apopto- sis, antigen processing, cell adhesion molecules). The book has also had to encompass areas of a more general flavor to provide balance for the general reader (such as reviews of macrophage development, heterogeneity, and function, and of the surface molecules expressed by macrophages). I thank all the authors for their prompt sub- missions; all have been of high quality, and my editorial tasks, thankfully, have been minimal. Michael A. Horton London, United Kingdom ix Contents Chapter J An Overview of Receptors of MPS Cells lain Fraser and Siam on Gordon 1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2. The Mononuclear Phagocyte System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Diversity of Macrophage Plasma Membrane Receptors. . . . . . . . . . . . . . . . 6 3. 1 A Structural Approach to Classification . . . . . . . . . . . . . . . . . . . . . . . . . . 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3. 2 Multisubunit Receptors 3. 3 Soluble Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3. 4 Lectins and Lectin-Like Receptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4. Functions and Selected Examples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4. 1 Growth, Differentiation, and Modulation . . . . . . . . . . . . . . . . . . . . . . . . 14 4. 2 Cell-Cell and Cell-Matrix Interactions. . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4. 3 Endocytosis and Scavenger Receptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4. 4 Secretory Responses and Biosynthesis of Effector Molecules . . . . . . 17 5. Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6. References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 . . . . . . . . . . . . . . . . . . . .