On the cover: Three-dimensional structure of complement component C1 derived from modeling and binding studies. This structure represents the active conformation, in which the C1rs tetramer (multicolored) lies in a horizontal plane relative to the six C1q stalks (grey). The C1rs protease domains (not shown) are located in the center of the complex. Phillips, A. E., J. Toth, A. W. Dodds, U. V. Girija, C. M. Furze, E. Pala, R. B. Sim, K. B. M. Reid, W. J. Schwaeble, R. Schmid, A. H. Keeble, and R. Wallis. 2009. Analogous interactions in initiating complexes of the classical and lectin pathways of complement. J. Immunol. 182: 7708–7717.