The SICA (schizont-infected cell agglutination) proteins of P. knowlesi, one of the variant antigen gene families, are associated with parasitic virulence. These proteins are comprised of multiple domains, with the extracellular domains occurring at different frequencies. There can be between 1 and 10 copies of this cysteine-rich domain [1].

1: The genome of the simian and human malaria parasite Plasmodium knowlesi. Pain A, Bohme U, Berry AE, Mungall K, Finn RD, Jackson AP, Mourier T, Mistry J, Pasini EM, Aslett MA, Balasubrammaniam S, Borgwardt K, Brooks K, Carret C, Carver TJ, Cherevach I, Chillingworth T, Clark TG, Galinski MR, Hall N, Harper D, Harris D, Hauser H, Ivens A, Janssen CS, Keane T, Larke N, Lapp S, Marti M, Moule S, Meyer IM, Ormond D, Peters N, Sanders M, Sanders S, Sargeant TJ, Simmonds M, Smith F, Squares R, Thurston S, Tivey AR, Walker D, White B, Zuiderwijk E, Churcher C, Quail MA, Cowman AF, Turner CM, Rajandream MA, Kocken CH, Thomas AW, Newbold CI, Barrell BG, Berriman M; Nature. 2008;455:799-803. PMID:18843368