A Jak3 Mutation Protects against Cerebral Malaria Figure 6. Cell transfer experiments to induce susceptibility to cerebral malaria in Jak3W81R mice. Wild type C57BL/10J (B10) mice, Jak3W81R homozygote mutants (Fig. 6A), or Jak3W81R homozygote mutants having received the indicated cell populations (20 million total splenocytes or 5 million each of the indicated cell population; 2 hrs prior to infection); (Fig. 6A, 6B, 6C) were infected i.v. with 106 P. berghei ANKA-parasitized RBCs, and survival from infection was monitored. Untreated wild type B10 and Jak3W81R mutants were used as susceptible and resistant controls, respectively. All surviving mice were sacrificed on day 15 post-infection (experimental end-point). Data represent 2 independent experiments. doi:10.1371/journal.pone.0031012.g006 agrees with such a model, with partial CM-protection in Jak3W81R/+ heterozygotes being linked to an intrinsic cell autonomous defect of Jak3W81R/+ T/B/NK cells which are present in normal numbers in these mice. Finally, a similar scenario has been previously proposed to account for incomplete penetrance and/or partial expressivity of the human SCID phenotype caused by homozygosity for loss of function JAK3 mutations in certain familial cases [52]. What would be the molecular basis of a dominant-negative effect of W81R on Jak3 function? Ligand-induced oligomerization of cytokine receptors and associated Jak3 kinases may position wild type and mutant Jak3 variants in close proximity in a signaling complex. In this context, inter-molecular dominant negative effects of gain-of-function Jak3 alleles such as W81R may alter the function of the wild type protein expressed in the same cell. W81 maps in the amino-terminal FERM domain, and several FERM domain mutations have been reported in SCID patients, including M1V, A58P, Del58A, 203DelG, Y100C, D169E and P151R [41,53,54]. The study of these and other site-directed FERM domain mutants indicate that this domain plays a key role in multiple aspects of Jak3 function ([54], reviewed in [55]). It is required for membrane targeting and for interaction with the gc chain of cytokine receptor [54,56]. It also acts as a positive regulator of Jak3 kinase activity: it physically interacts with the JH1-JH2 kinase domain to stimulate both ATP binding and tyrosine phosphorylation [54]. Such interactions may be critical in the early cross-phosphorylation of Jak kinases that normally precedes phosphorylation of neighboring substrates [57]. A PLoS ONE | www.plosone.org 9 February 2012 | Volume 7 | Issue 2 | e31012