Variation of Pneumococcal Pilus-1 Expression Results in Vaccine Escape during Experimental Otitis Media [EOM]

Abstract

The pneumococcal Pilus-1 enhances attachment to epithelial cells in the respiratory tract and subsequent invasion. Pilus-1 expression is bi-stable and positively regulated by the RlrA transcriptional regulator. To delineate the role of pilus-1 in Experimental Otitis Media (EOM), we evaluated colonization and disease due to a Streptococcus pneumoniae (SP) wild type strain (Taiwan19F-14 wt) and its otherwise isogenic pilus-1 and pilus-2 deficient mutant (Taiwan19F-14 ΔPI-1/PI-2-) as well as potential for a chimeric protein (RrgB321) vaccine candidate for prevention of middle ear (ME) disease.MethodsChinchillas were challenged intranasally with either Taiwan19F-14 wt or Taiwan19F-14PI-1/PI-2 deficient mutant. ME status was assessed and direct cultures performed. New cohorts of animals were immunized with RrgB321 or alum. Intranasal challenge with Taiwan19F-14 wt [erythromycin susceptible E(S)] was performed. Subsequently, a second cohort of animals was immunized and challenged with either Taiwan19F-14 wt or a Pilus-1 over-expressing mutant [Taiwan19F-14+pMU1328_Pc-rlrA mutant; E resistant (R)] strain. Pilus-1 expression was analyzed in SP isolated from nasopharynx (NP) and ME fluids by flow cytometry.ResultsCulture positive EOM developed following challenge with either wild type SP (Taiwan19F-14) or its pilus-1 deficient mutant. Culture positive EOM developed following challenge with wild type in both RrgB321 immunized and control animals. Pilus-1 expression in ME fluids was significantly higher in controls compared to immunized chinchillas. In second cohort of immunized and control animals challenged with the over-expressing Pilus-1 mutant, delayed development of EOM in the immunized animals was observed. Pneumococci recovered from ME fluid of immunized animals were no longer E(R) signifying the loss of the pMU1328_Pc-rlrA plasmid.ConclusionPneumococcal pilus-1 was not essential for EOM. Regulation of Pilus-1 expression in ME fluids in the presence of anti RrgB321 antibody was essential for survival of S. pneumoniae. Pneumococci have evolved mechanisms of regulation of non-essential surface proteins to evade host defenses.

Streptococcus pneumoniae Type 1 Pilus – A Multifunctional Tool for Optimized Host Interaction

“…Within the growing list of negative regulators ( Basset et al, 2011 ; Kreikemeyer et al, 2011 ; Herbert et al, 2015 ), some of them might require additional validation ( Basset et al, 2017 ). Detailed investigations with extending systems that reflect the in vivo situation as closely as possible will help to further clarify the overall context of pneumococcal P1 regulation during host colonization and invasion ( Pancotto et al, 2013 ; Figueira et al, 2014 ). The described absence of P1 expression below 31°C indicates the importance of host environmental factors on P1 regulation ( Basset et al, 2017 ).…”

Molecular characterization of Streptococcus pneumoniae, particularly serotype19A/ST320, which emerged in Krasnoyarsk, Russia

“…Regarding pneumococcal surface proteins (9)(10)(11)(12), two types of pneumococcal pili, PI-1 and PI-2, have been identified. The major backbone subunit of PI-1 is the RrgB protein, the expression of which (gene, rrgB) is regulated by the rlrA gene (15)(16)(17)(18). PI-1 is present only in certain pneumococcal CCs.…”

Panel 6: Vaccines

“…59 Immunization of chinchillas with the chimeric protein RrgB321, a component of pneumococcal pilus 1, did not protect against experimental OM, although a delay in development of disease was seen. 60 …”

“…59 Immunization of chinchillas with the chimeric protein RrgB321, a component of pneumococcal pilus 1, did not protect against experimental OM, although a delay in development of disease was seen. 60 Some laboratories have attempted to develop whole-cell pneumococcal vaccines. A live whole-cell vaccine lacking FtzY (to stop multiplication of the bacteria) produced serotype-independent protection against OM that was CD41 T cell dependent.…”

“…Two conserved proteins of unknown function, SP1298 and SP2205, were not directly tested for prevention of AOM but were used to immunize mice, and they showed a reduced pneumococcal load in the nasopharynx, lungs, and blood 59 . Immunization of chinchillas with the chimeric protein RrgB321, a component of pneumococcal pilus 1, did not protect against experimental OM, although a delay in development of disease was seen 60 …”