EVIDENCE FOR THE SIMULTANEOUS EXPRESSION OF 2 PSPAS BY A CLONE OF CAPSULAR SEROTYPE 6B STREPTOCOCCUS-PNEUMONIAE

Pneumococcal surface protein A (PspA) has been shown to be a serologic ally variable virulence factor of Streptococcus pneumoniae. In mice, P spA can elicit antibodies capable of protecting them against otherwise fatal infections with encapsulated pneumococci. In previous studies i t has been reported that almost all isolates have two apparently unlin ked genomic sequences that are highly homologous to the 5' and 3' halv es of Rx1 pspA, although out MAbs to PspA have not detected more than one PspA in any given isolate of S. pneumoniae. Recently, we have iden tified four isolates from a clone of capsular serotype 6B pneumococci (MC25-28) that simultaneously express two distinct PspAs. Each of the isolates (MC25-28) exhibited the same two Kpn I fragments (each contai ning a Hind III site) that hybridized with Rx1 pspA. MAbs specific for PspA detected two PspAs characterized by different molecular weights and different serologic patterns of reactivity (PspA type 6 detected b y MAbs XiR278 and 2A4, and PspA type 34 detected only by MAb 7D2) in e ach of the four isolates. In previous studies XiR278 and 2A4 frequentl y have been observed to react with PspA epitopes of the same strain. B ased on molecular weight data both epitopes were always present on the same molecule. Our present findings raise the possibility that pneumo cocci make a second serologically variable PspA which is generally not detected by currently available MAbs to PspA. (C) 1996 Academic Press Limited.