Counteractive functions are encrypted in the residues of CD154.

CD40, as a single receptor that binds CD154 (CD40-ligand or CD40L), regulates counteractive effector functions such as production of pro- and anti-inflammatory cytokines. Therefore, we examined whether such dual messages are encrypted in CD40L. As such message encryption was never investigated, we hypothesized that mutation of certain amino acid residues should in principle enhance pro-inflammatory cytokine production whereas mutation of some others would enhance anti-inflammatory cytokine secretion. We mutated six such residues, which were previously showed to participate in CD40L function. Here, we report that the mutant CD154 129E→V was superior to the wild-type CD154 in killing of Leishmania donovani, induction of inducible nitric oxide synthase (iNOS) and production of IL-12 and relative phosphorylation of p38MAPK and ERK-1/2 in PBMC-derived macrophages. By contrast, 128S→V promoted L. donovani survival, reducing iNOS, but increasing IL-10 expression and predominant ERK-1/2 phosphorylation. The mutant 144G→V did not have significant effects. Other mutants (142E→V, 143K→A, 145Y→F) mimicked the wild-type CD154. Molecular dynamics simulation suggested that these mutations induced differential conformational changes in the CD40-CD154 complex. Therefore, assortment of the contrasting messages encrypted in a given ligand performing counteractive functions presents a novel fundamental biological principle that can be used for devising various therapies.