Immunoblot of recombinant pneumococcal surface protein A (PspA). Lanes: 1 and 2, phage lysate from full-length PspA+ clone with and without induction by isopropyl-ß-D-thiogalactopyranoside (IPTG), respectively; 3, cell wall extract from pneumococcal type 2 strain D39.   (McDaniel L. et al. 1991 PspA, A surface protein of Streptococcus pneumoniae, is capable of eliciting protection against Pneumococci of more than one capsular type. Infection and Immunity 59: 222-228.)