Protection against Streptococcus pneumoniae elicited by immunization with pneumolysin and CbpA

The need for the development of cheap and effective vaccines against pneumo coccal disease has necessitated the evaluation of common virulence-associat ed proteins of Streptococcus pneumoniae as potential vaccine antigens. In t his study, we examined the capacity of active immunization with a genetic t oxoid derivative of pneumolysin (PdB) and/or a fragment of choline binding protein A (CbpA; also known as PspC, Hic, and SpsA) to protect mice from in traperitoneal challenge with medium to very high doses of a highly virulent capsular type 2 pneumococcal strain, D39. The median survival times for mi ce immunized with the individual protein antigens in different adjuvant com binations were significantly longer than those for mice that received the r espective adjuvants alone. Mice immunized with CbpA alone were significantl y better protected than mice immunized with PdB alone. Correspondingly, the median survival times for mice that were immunized with a combination of P dB and CbpA were significantly longer than those for mice that received PdB alone but not significantly different from those that received CbpA alone. Mice immunized with the protein antigens in a mixture of monophospholipid A (MPL) and aluminium phosphate (AlPO4) adjuvants had higher antibody titer s than mice that received the antigens in AlPO4 alone. Mice immunized with PdB in MPL plus AlPO4 were also significantly better protected than mice th at received PdB in AlPO4 alone.