Cover photograph (Copyright © 2000, American Society for Microbiology. All rights reserved.): Structure model of the vaccinia virus complement control protein VCP, which can inhibit classical and alternative pathways of complement activation. The ability of the protein to bind heparin results in additional functions, including uptake by mast cells, blockage of antibody binding to endothelial cells, and protection of xenoendothelial cells from killing by natural killer cells. The heparin binding sites are shown in magenta, yellow, blue, and red. Short consensus repeat domains 1 to 4 are alternately shaded grey and white. (See the related article in the June 2000 issue: vol. 74, p. 5659-5666.)