Immunization with PspA incorporated into a poly(ethylene oxide) matrix elicits protective immunity against Streptococcus pneumoniae

Immunization with pneumolysin protects against both retinal and global damage caused by Streptococcus pneumoniae endophthalmitis

PURPOSE

To determine whether immunization with pneumolysin (PLY) protects against pneumococcal endophthalmitis.

METHODS

New Zealand white rabbits were immunized with a mutant form of PLY that retains only 1% of its cytolytic activity until serum IgG titers were ≥51,200. For a negative control, rabbits were immunized with phosphate-buffered saline (mock). Each vitreous was injected with 10(2) colony-forming units of a clinical endophthalmitis isolate of Streptococcus pneumoniae. Severity of endophthalmitis was graded by slit lamp examination at 24 and 48 h postinfection (PI). Serial dilutions of vitreous were plated for bacterial colony-forming units quantitation, eyes were extracted for histology, and a whole blood survival assay was performed.

RESULTS

Immunized rabbits had a significantly lower mean slit lamp examination score at 24 and 48 h PI when compared to mock immunized rabbits (P ≤ 0.002). There was not a significant difference in bacterial load in the vitreous at 24 or 48 h PI. Histological sections showed that retinas of mock immunized rabbits appeared to be destroyed, whereas those of PLY immunized rabbits remained largely intact. Damage spread to the aqueous humor, stroma, and conjunctiva of mock immunized rabbits by 48 h PI. Minimal damage was observed in the vitreous of PLY immunized rabbits and did not spread to other parts of the eye. Whole blood from immunized rabbits inhibited the growth of bacteria better than whole blood from mock immunized rabbits.

CONCLUSION

Immunization with PLY helps protect the eye from damage caused by pneumococcal endophthalmitis.

Pneumococcal surface protein A contributes to secondary Streptococcus pneumoniae infection after influenza virus infection

We compared the growth of Streptococcus pneumoniae mutants with a disruption in the gene for either pneumococcal surface protein A (PspA-), neuraminidase A (NanA-), or hyaluronidase (Hyl-) to that of the parental strain D39 by means of a competitive growth model in mice with and those without prior influenza virus infection. The numbers of total bacteria recovered from mice with prior influenza virus infection were significantly greater than those recovered from mice without prior influenza virus infection. Although the Hyl- and NanA- mutants did not display attenuation in mice with or without prior influenza virus infection, the PspA- mutant exhibited attenuation both in mice with and in mice without prior influenza virus infection. This defect was severe in influenza virus-infected mice, for which growth of the PspA- mutant was 1800-fold lower than that of the parental strain D39. Furthermore, PspA immunization significantly reduced secondary bacterial lung burdens and concentrations of specific markers of lung damage in mice receiving serotypes 2, 3, and 4 pneumococci. Our findings indicate that PspA contributes to secondary S. pneumoniae infection after influenza virus infection and that PspA immunization mitigates early secondary pneumococcal lung infections.

Initial and subsequent response to pneumococcal polysaccharide and protein-conjugate vaccines administered sequentially to adults who have recovered from pneumococcal pneumonia

BACKGROUND

Controversy persists over the benefits of pneumococcal polysaccharide vaccine (PPV) for adults at high risk for pneumococcal disease. We studied PPV, protein-conjugate pneumococcal vaccine (PCV), and immunologic "priming" with PCV followed by "boosting" with PPV in adults who had recovered from pneumococcal pneumonia.

METHODS

Subjects received PPV followed by PCV 6 months later, or vice versa. The levels of IgG to capsular polysaccharide and opsonophagocytic killing activity (OPK) were studied at baseline and at 4-8 weeks and 6 months after each vaccination.

RESULTS

PPV and PCV stimulated similar IgG levels and OPK at 4-8 weeks after vaccination. Six months after receipt of PPV, the antibody levels declined to baseline but remained modestly elevated after receipt of PCV. PCV administered 6 months after PPV stimulated modest increases in IgG level that failed to reach the peaks observed after receipt of PPV. In contrast, PPV administered 6 months after PCV caused dramatic increases in the levels of IgG and OPK for all polysaccharides at 4-8 weeks, consistent with a booster effect. Six months after receipt of the second vaccination, however, levels of IgG and OPK fell precipitously in all patients, approaching baseline levels.

CONCLUSIONS

In these high-risk subjects who have recovered after treatment for pneumonia, the effect of PPV is short-lived; PCV stimulates a more prolonged response. The use of PPV as a booster following PCV causes early increases in antibody levels, but the level of IgG declines rapidly thereafter, consistent with induction of suppressor cells or tolerance. Protein vaccines may be needed for high-risk adults.