Counteractive functions are encrypted in the residues of CD154

Area of Science:

• Immunology
• Molecular Biology
• Biochemistry

Background:

• CD40-ligand (CD154) binding to CD40 regulates opposing immune functions, including cytokine production.
• The hypothesis that CD154 encrypts dual messages, dictating either pro- or anti-inflammatory responses, was unexplored.

Purpose of the Study:

• To investigate whether CD154's dual messaging capability can be modulated through specific amino acid mutations.
• To determine if distinct mutations enhance pro-inflammatory or anti-inflammatory cytokine secretion and impact immune cell function.

Main Methods:

• Site-directed mutagenesis was employed to alter six amino acid residues in CD154 previously implicated in its function.
• The functional effects of CD154 mutants were assessed in vitro using peripheral blood mononuclear cell (PBMC)-derived macrophages.
• Key assays included Leishmania donovani killing, inducible nitric oxide synthase (iNOS) induction, cytokine (IL-12, IL-10) production, and MAPK phosphorylation (p38MAPK, ERK-1/2).
• Molecular dynamics simulations were used to analyze conformational changes in the CD40-CD154 complex.

Main Results:

• Mutant CD154 129E→V enhanced Leishmania donovani killing, iNOS production, IL-12 secretion, and p38MAPK/ERK-1/2 phosphorylation.
• Mutant CD154 128S→V promoted parasite survival, reduced iNOS, increased IL-10, and favored ERK-1/2 phosphorylation.
• Mutant 144G→V showed no significant effects, while mutants 142E→V, 143K→A, and 145Y→F mimicked wild-type CD154.
• Molecular dynamics simulations indicated that mutations induced distinct conformational changes in the CD40-CD154 complex.

Conclusions:

• Specific amino acid residues within CD154 encrypt distinct functional messages, allowing for differential modulation of immune responses.
• The ability to selectively enhance pro- or anti-inflammatory pathways by altering CD154 offers a novel principle for developing targeted immunotherapies.