Toll-like receptors (TLRs) expressed on antigen-presenting cells (APCs), form a critical link between innate and the adaptive immune responses. Activation of TLRs by LPS and dsRNA results in up-regulation of co-stimulatory molecules (UCM) essential for the generation of robust T-cell responses. It is now evident that type I interferons (IFNs) play an important role in UCM and in the subsequent maturation of APCs. The recently identified adaptor molecules Trif and Tram, unlike their counterparts MyD88 and MAL/Tirap, induce type I IFN via the TLR4 signaling pathway, whereas Trif appears to be the sole adaptor molecule involved in TLR3 signaling, resulting in subsequent production of type I IFN. Here, we discuss how Trif and type I IFN are involved in the optimization of APC-T cell interaction in response not only to viral but also bacterial stimuli.