Cholesterol-dependent cytolysins, (CDC), are a family of toxins produced by Gram-positive bacteria that produce large pores on cell membranes containing cholesterol. Over twenty species of bacteria produce CDCs including; Streptococcus, Listeria, Clostridium, Bacillus and Arcanobacterium. Even though the main action of the toxins is pore generation, the toxins also interfere with immune cell function as well as modulating cytokine induction (Billington et al., 2000). One prominent member of the CDCs is pneumolysin (PLY) which is produced from the pathogen Streptococcus pneumoniae. PLY is known to have various immunomodulatory properties resulting in the production of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6 and IL-8) (Malley et al., 2003). It was recently shown that PLY is also able to act as a mucosal adjuvant when genetically fused to either enhanced green fluorescent protein, eGFP, or an Streptococcus pneumoniae antigen (Douce et al., 2010). To establish if the immunogenic/self adjuvant characteristic displayed by PLY is unique, selected CDC family members were genetically fused to the model antigen, eGFP, and investigated by immunization of mice with the individual toxins or with the toxin fusion proteins. The central theme of this thesis was to establish whether the selected CDCs suilysin (SLY), perfringolysin (PFO) and intermedilysin (ILY) possess similar immunogenic and adjuvant properties that PLY has been shown to possess and thus try to elucidate a possible mechanism for the adjuvant activity. The family member PFO, which demonstrates similar binding and toxicity to PLY was shown to act as a mucosal adjuvant to the genetically fused antigen, with anti eGFP titres comparable to those achieved by vaccination with eGFP-PLY. Interestingly the human specific family member ILY, which was unable to bind or lyse non human cells, also demonstrated some mucosal adjuvant activity when tested at a high dose. Following vaccination with the eGFP fusion proteins no anti CDC responses were detected. Immunogenic analysis of the purified individual proteins also demonstrated an inability to generate a specific anti-CDC immune response following intranasal administration of the tested dose. The individual proteins inability to stimulate a mucosal immune response highlights the role the fusion of the two proteins play in the generation of an immune response. Generation of chimeric proteins between the members PLY and ILY and subsequent adjuvant analysis demonstrated the requirement of cell binding for PLY’s adjuvant activity. The addition of cell binding capabilities to ILY did not result in an enhanced adjuvant response indicating that PLY and ILY activate the intranasal immune response by different mechanisms.