Epitope analyses of pneumococcal surface protein A: a combination of two monoclonal antibodies detects 94% of clinical isolates

Immunisation of BALB/c mice with seven heat-treated Norwegian clinical isol ates of Streptococcus pneumoniae of different serotypes elicited mainly mon oclonal antibodies (mAbs) to pneumococcal surface protein A (PspA). It was remarkable that the fusions resulted only in a few mAbs directed against ot her protein antigens. Dot blot analysis with 16 mAbs using clinical isolate s representing 23 different capsular types and the uncapsulated reference s train R36A showed that some or the mAbs bound to PspA epitopes expressed by a low number of strains whereas others bound to broadly distributed epitop es. On the basis of their reactivities, seven of these mAbs could be divide d into two groups recognising different subsets of pneumococci. The three m Abs in the narrow reacting group bound to epitopes found in 21-25%. of the strains whereas the four mAbs in the broad reacting group detected more tha n 57% of the analysed strains. The epitopes for these seven antibodies were surface exposed on live exponential phase grown pneumococci as shown by fl ow cytometry. The finding that a combination of mAb 180.C-1 (IgG2a) from th e first group and mAb 170,E-11 (IgG2a) from the second group detected 94%, of the examined strains is interesting because PspA has been reported by ot hers to be a serological. highly variable protein. (C) 2001 Federation of E uropean Microbiological Societies. Published by Elsevier Science B.V. All r ights reserved.