Fig. 9. Receptor complex activation by CNTF and CLC. (A) CNTF is released by trauma and activates its tripartite receptor complex. (B) CLF expression is required for CLC secretion, and the hetero complex displays activities on the tripartite CNTF receptor complex. (C) CLC associates with CNTFR within the cells before being secreted and activates the gp130–LIFR signalling complex. Stoichiometric studies indicate that in (A) and (C), at least a portion of the ligands (CLC or CNTF) dimerize and associate with two molecules of CNTFR. For CLC–CLF, the protein ratio involved in the formation of the composite cytokine is not yet known.