In vivo and In vitro Regulation of Type I IFN Synthesis by Synergistic Effects of CD40 and Type II IFN

During cognate interaction with CD40 ligand (CD154)-expressing T cells, Ag-presenting accessory cells are activated for increased cytokine synthetic and costimulatory function. We examined whether CD40 modulates in vivo innate immune function over time, hypothesizing that distinct cytokine responses evolve to delayed microbial exposure. C3H/HeN mice pretreated with activating anti-CD40 Ab (FGK45) produced 10-fold more serum IFN-γ and IL-12 p70 to delayed, but not synchronous, challenge with LPS. A novel finding was that LPS-induced IFN-α increased by 20-fold in mice pretreated for 24 h, but not 6 h or less, with anti-CD40. Anti-CD40-pretreated C57BL/6 RAG-2 −/− mice similarly increased IFN-α responses to delayed LPS challenge, confirming mediation by innate immunity. Type I IFNR- and IFN-γ-deficient mice treated with anti-CD40 failed to expand serum IFN-α responses to LPS challenge. Combined pretreatment with anti-CD40 and anti-IFN-γ mAb showed that IFN-γ produced after anti-CD40 pretreatment, but before LPS challenge, was necessary for IFN-α synthetic enhancement. Anti-CD40 also increased polyinosinic-polycytidylic acid (poly(I:C))-inducible IFN-α by 5-fold in an IFN-γ-dependent fashion, but did not significantly increase IFN-α production to CpG or Pam 3 Cys challenges. Poly(IC)-stimulated splenocytes from anti-CD40-pretreated mice produced 4-fold more IFN-α than controls and production associated with CD11c + cells. Finally, rIFN-γ and anti-CD40 combined synergistically to increase poly(IC)-inducible IFN-α synthetic capacity in bone marrow dendritic cells. We conclude that innate immune production of IFN-α is cooperatively regulated by CD40 and IFN-γ acting on dendritic cells, suggesting a unique mechanism by which innate immune function evolves in response to specific adaptive immune signals.