Maternal immunization with pneumococcal surface protein A protects against pneumococcal infections among derived offspring

Pathogen-specific antibody plays an important role in protection against pneumococcal carriage and infections. However, neonates and infants exhibit impaired innate and adaptive immune responses, which result in their high susceptibility to pneumococci. To protect neonates and infants against pneumococcal infection it is important to elicit specific protective immune responses at very young ages. In this study, we investigated the protective immunity against pneumococcal carriage, pneumonia, and sepsis induced by maternal immunization with pneumococcal surface protein A (PspA). Mother mice were intranasally immunized with recombinant PspA (rPspA) and cholera toxin B subunit (CTB) prior to being mated. Anti-PspA specific IgG, predominantly IgG1, was present at a high level in the serum and milk of immunized mothers and in the sera of their pups. The pneumococcal densities in washed nasal tissues and in lung homogenate were significantly reduced in pups delivered from and/or breast-fed by PspA-immunized mothers. Survival after fatal systemic infections with various types of pneumococci was significantly extended in the pups, which had received anti-PspA antibody via the placenta or through their milk. The current findings strongly suggest that maternal immunization with PspA is an attractive strategy against pneumococcal infections during early childhood.     

Specific cross-protective antigonococcal immunity in the murine genital tract

Specific acquired immunity to gonococci was studied in systemically immunized mice, challenged with 10(7) gonococci by intrauterine inoculation. Protection after intraperitoneal immunization was monitored by vaginal cultures taken 24 h post-challenge, since events during the first 24 h postexposure to gonococci are crucial in determining the outcome of infection. Mice were protected against gonococcal challenge by two inoculations with either live or boiled gonococci given 4 weeks apart, whereas immunization with one inoculation did not protect against challenge 1 week later. Protection was correlated with high titers of IgG antibody in serum after two immunizations, but not with the high titers of serum IgM antibody found after the one immunization. IgG antibodies, but not IgM antibodies, were shown to pass into genital secretions. Protection could be passively transferred by serum with high titers of antibody. Of most practical importance was the finding that not only were heat-stable antigens protective, but also heterologous protection resulted after immunization with three strains differing in source (disseminated gonococcal infection versus gonorrhea), opacity-transparency characteristics, and serum sensitivity. The data indicate that IgG antibodies resulting from systemic immunization with heat-stable antigens may be able to provide cross-protection immunity against gonorrhea.     

Oral immunization with recombinant Lactococcus lactis confers protection against respiratory pneumococcal infection

In the present work, we evaluated if oral immunization with the pneumococcal protective protein A (PppA), expressed in the cell wall of Lactococcus lactis (L. lactis PppA+), was able to confer protective immunity against Streptococcus pneumoniae. Mice were immunized orally with L. lactis PppA+ for 5 consecutive days. Vaccination was performed one (nonboosted group) or 2 times with a 2 week interval between each immunization (boosted group). Oral priming with L. lactis PppA+ induced the production of anti-PppA IgM, IgG, and IgA antibodies in serum and in bronchoalveolar (BAL) and intestinal (IF) lavage fluids. Boosting with L. lactis PppA+ increased the levels of mucosal and systemic immunoglobulins. Moreover, the avidity and the opsonophagocytic activity of anti-PppA antibodies were significantly improved in the boosted group. The presence of both IgG1 and IgG2a anti-PppA antibodies in serum and BAL and the production of both interferon gamma and interleukin-4 by spleen cells from immunized mice indicated that L. lactis PppA+ stimulated a mixture of Th1 and Th2 responses. The ability of L. lactis PppA+ to confer cross-protective immunity was evaluated using challenge assays with serotypes 3, 6B, 14, and 23F. Lung bacterial cell counts and hemocultures showed that immunization with L. lactis PppA+ improved resistance against all the serotypes assessed, including serotype 3, which was highly virulent in our experimental animal model. To our knowledge, this is the first demonstration of protection against respiratory pneumococcal infection induced by oral administration of a recombinant lactococcal vaccine.     

Inhibition of antibody responses to phosphocholine by C-reactive protein

C-reactive protein (CRP) is an acute phase serum protein in man that binds to the cell wall C-polysaccharide (PnC) of Streptococcus pneumoniae via phosphocholine (PC) determinants. We have previously shown that in mice CRP increases splenic clearance of PnC-coated autologous erythrocytes and S. pneumoniae, and increases survival after pneumococcal infection. Because CRP alters clearance of particulate PnC antigens, we tested its effect on immunization with pneumococci. Pretreatment of mice with 50 to 200 micrograms CRP 30 min before immunization with serotype 3 S. pneumoniae resulted in dose-dependent inhibition of the antibody response to PC. Both serum hemagglutinin and splenic PFC against PC were decreased in CRP-treated mice tested from 1 to 10 days after injection of antigen. CRP treatment had no effect on the antibody response to the serotype 3 capsular polysaccharide, another T-independent antigen. To determine whether CRP inhibition was related to altered processing of particulate antigen, mice were immunized with horse red blood cells (HRBC) conjugated with PC or PnC and the PFC responses to PC and HRBC were determined. CRP treatment resulted in specific inhibition of the PFC response to PC in both cases without affecting the response to HRBC. These results indicate that inhibition of the antibody response by CRP is not the result of altered antigen localization and processing, and that CRP may prevent immunization by masking determinants on bacterial or other surfaces.     

Antibody against the antigen receptor of a plasmacytoma prolongs survival of mice bearing the tumor.

A transplantable plasmacytoma, TEPC-15 in BALB/c mice, induces a transient antibody response directed against the combining region of the myeloma protein produced by the tumor. Mice immunized with mitomycin-treated tumor cells produce similar antibody but do not develop tumor; mice so immunized survive longer than untreated mice when inoculated with viable TEPC-15 cells. This protection afforded by immunization can be transferred by serum alone; the protective effect of passively given serum is eliminated by absorbing out antibody directed against the myeloma protein.     

Induction of immune response to Streptococcus pneumoniae by administration of oral viridans streptococci via phosphorylcholine determinant

Expression of the phosphorylcholine (PC) epitope was examined in 48 viridans streptococcal strains, including Streptococcus pneumoniae R36a as the positive control, and their immunogenicity to induce an S. pneumoniae-cross-reactive response was evaluated in mice. Thirteen strains were found to express the PC epitope, while no obvious association was found between the taxonomic categories and PC expression. Serum antibody responses to S. pneumoniae cells were induced in mice by intraperitoneal injection of the PC-positive, but not PC-negative, strains. The cross-reactive antibodies induced by non-pneumococcal oral streptococci were readily inhibited by free hapten PC. IgM was the sole isotype of the anti-pneumococcal and anti-PC antibodies, and the phenomenon of immunological memory was not observed. Since the anti-PC antibody is critically important for resistance against pneumococcal infection in mice, the present results indicate the possibility that PC-expressing oral commensal bacteria have a significant influence on the hosts' responsiveness to S. pneumoniae.     

Intratracheal immunization with pili protein protects against mortality associated with Pseudomonas aeruginosa pneumonia in mice

We examined the protective effect of intratracheal immunization with Pseudomonas aeruginosa pili protein against respiratory infection caused by P. aeruginosa. Mice were immunized intratracheally or subcutaneously with purified pili protein or bovine serum albumin as a control. Intratracheally but not subcutaneously pili protein-immunized mice showed significant improvement of survival after intratracheal challenge with the PAO1 strain. Furthermore, bacterial cell counts in pili protein-immunized murine lungs were significantly decreased compared to controls at 18 h after the challenge. Antipili protein antibody titers in bronchoalveolar lavage fluid of intratracheally pili protein-immunized mice were higher than in bovine serum albumin immunized mice. However, antipili antibody titers were not increased in bronchoalveolar lavage fluid of subcutaneously pili protein-immunized mice, despite the high serum antipili antibody titers. Inoculation of P. aeruginosa induced immediate increases in interleukin-12 and interferon-gamma in bronchoalveolar lavage fluid of pili protein-immunized mice, reflecting an adequate and rapid immune response against P. aeruginosa respiratory tract infection. Our findings suggest that intratracheal pili protein immunization is effective against respiratory tract infection caused by P. aeruginosa in mice.     

重组质粒pcDNA3-dnaJ/蛋白DnaJ异源免疫诱导Th1和Th17细胞免疫应答抵抗肺炎链球菌感染 *

目的 探索更有效的肺炎链球菌DNA疫苗和疫苗免疫策略,并探究其中的保护机制。方法 构建重组质粒pcDNA3-dnaJ并表达DnaJ蛋白,实验分别设置重组质粒pcDNA3-dnaJ/蛋白DnaJ免疫小鼠组及单独质粒pcDNA3-dnaJ免疫小鼠组,分别比较肺炎链球菌菌株攻毒后小鼠鼻腔灌洗液细菌载量及生存率,采用ELISA检测免疫小鼠血清抗体效价及炎症因子,流式细胞术分析体外BMDCs激活情况及Th1和Th17细胞免疫应答。结果 质粒pcDNA3-dnaJ免疫3次可诱导血清中抗原特异性抗体的产生,并减少肺炎链球菌攻毒后鼻咽部的细菌载量,但在防止致死性感染方面效果较差。然而,与重复质粒DNA接种三次相比,pcDNA3-dnaJ 1次/ DnaJ蛋白加强1次的免疫策略可以显著减少鼻咽中的肺炎链球菌定植,并能够更好的预防致死性感染。此外,与DNA质粒加强免疫相比,DnaJ蛋白加强免疫后可产生更高水平的IFN-γ和IL-17A。结论 重组质粒pcDNA3-dnaJ/蛋白DnaJ异源免疫可能通过活化树突状细胞,进而诱导Th1和Th17细胞免疫应答,抵抗肺炎链球菌感染。     

Determinants of immunity to murine salmonellosis: studies involving immunization with lipopolysaccharide-lipid A-associated protein complexes in C3H/HeJ mice

We have earlier demonstrated that the C3H/HeJ Salmonella hypersusceptible mouse can be protected against infection with this organism by prior immunization with lipopolysaccharide (LPS)-lipid A-associated protein (LAP) complexes, but not with LPS alone. In the current studies, protection has been shown to correlate with the induction of LPS-specific antibody in immunized mice. LPS was demonstrated to be a relevant target antigen for Salmonella immunity since C3H/HeJ mice were afforded higher survival rates when they were challenged with Salmonella that shared the same LPS O-antigen as the vaccine. Although low levels of LPS-specific antibody can be detected 14 days after immunization with LAP-LPS, significant antibody is present only after 21-28 days. In addition, anti-LAP specific antibodies can be detected after 14 days of immunization with LAP-LPS. Adoptive transfer of either day 28 anti-LAP-LPS immune serum or day 28 LAP-LPS immune splenocytes alone to naive recipients affords mice minimal, if any, survival against lethal S. typhimurium LT2 challenge. In contrast, transfer of day 28 anti-LAP-LPS immune serum and day 28 LAP-LPS immune splenocytes together is able to transfer Salmonella immunity to naive C3H/HeJ mice. Further, equivalent transfer of only day 28 anti-LAP-LPS immune serum to C3H/HeJ mice immunized 7 days previously with LAP-LPS provides protection similar to that found in mice adoptively transferred with immune cells and serum. These results suggest that a host cellular factor or factors responsive to LAP-LPS, in addition to day 28 anti-LAP-LPS immune serum, may contribute to the protection afforded C3H/HeJ mice following immunization with LAP-LPS.     

Protection from Streptococcus pneumoniae infection by C-reactive protein and natural antibody requires complement but not Fc gamma receptors

Streptococcus pneumoniae is an important human pathogen and the most common cause of community-acquired pneumonia. Both adaptive and innate immune mechanisms provide protection from infection. Innate immunity to S. pneumoniae in mice is mediated by naturally occurring anti-phosphocholine (PC) Abs and complement. The human acute-phase reactant C-reactive protein (CRP) also protects mice from lethal S. pneumoniae infection. CRP and anti-PC Ab share the ability to bind to PC on the cell wall C-polysaccharide of S. pneumoniae and to activate complement. CRP and IgG anti-PC also bind to Fc gamma R. In this study, Fc gamma R- and complement-deficient mice were used to compare the mechanisms of protection conferred by CRP and anti-PC Ab. Injection of CRP protected wild-type, FcR gamma-chain-, Fc gamma RIIb-, and Fc gamma RIII-deficient mice from infection. Complement was required for the protective effect of CRP as cobra venom factor treatment eliminated the effect of CRP in both gamma-chain-deficient and wild-type mice, and CRP failed to protect C3- or C4-deficient mice from infection. Unexpectedly, gamma-chain-deficient mice were extremely sensitive to pneumococcal infection. This sensitivity was associated with low levels of natural anti-PC Ab. Gamma-chain-deficient mice immunized with nonencapsulated S. pneumoniae produced both IgM- and IgG PC-specific Abs, were protected from infection, and were able to clear the bacteria from the bloodstream. The protection provided by immunization was eliminated by complement depletion. The results show that in this model of systemic infection with highly virulent S. pneumoniae, protection from lethality by CRP and anti-PC Abs requires complement, but not Fc gamma R.     

Determinants of immunity to murine salmonellosis: studies involving immunization with lipopolysaccharide-lipid A-associated protein complexes in C3H/HeJ mice

Abstract We have earlier demonstrated that the C3H/HeJ Salmonella hypersusceptible mouse can be protected against infection with this organism by prior immunization with lipopolysaccharide (LPS)-lipid A-associated protein (LAP) complexes, but not with LPS alone. In the current studies, protection has been shown to correlate with the induction of LPS-specific antibody in immunized mice. LPS was demonstrated to be a relevant target antigen for Salmonella immunity since C3H/HeJ mice were afforded higher survival rates when they were challenged with Salmonella that shared the same LPS O-antigen as the vaccine. Although low levels of LPS-specific antibody can be detected 14 days after immunization with LAP-LPS, significant antibody is present only after 21–28 days. In addition, anti-LAP specific antibodies can be detected after 14 days of immunization with LAP-LPS. Adoptive transfer of either day 28 anti-LAP-LPS immune serum or day 28 LAP-LPS immune splenocytes alone to naive recipients affords mice minimal, if any, survival against lethal S. typhimurium LT2 challenge. In contrast, transfer of day 28 anti-LAP-LPS immune serum and day 28 LAP-LPS immune splenocytes together is able to transfer Salmonella immunity to naive C3H/HeJ mice. Further, equivalent transfer of only day 28 anti-LAP-LPS immune serum to C3H/HeJ mice immunized 7 days previously with LAP-LPS provides protection similar to that found in mice adoptively transferred with immune cells and serum. These results suggest that a host cellular factor or factors responsive to LAP-LPS, in addition to day 28 anti-LAP-LPS immune serum, may contribute to the protection afforded C3H/HeJ mice following immunization with LAP-LPS.     

Protective effect of antiganglioside antibodies against experimental Trypanosoma brucei infection in mice

Liposome-associated ganglioside antigens (ganglioside GM1 or bovine brain gangliosides) were prepared to facilitate the potential protective efficacy for Trypanosoma brucei. Mice were immunized with liposome-associated ganglioside GM1 or bovine brain gangliosides intraperitoneally (i.p.). After immunization, significantly higher antigen-specific IgG and IgM antibodies were detected in sera than in the nonimmunized control group. When sera from immunized mice were analyzed for isotype distribution, antigen-specific IgG1, IgG2a, and IgG3 antibody responses were also noted. After immunization, mice were challenged i.p. with 1 x 10(2) cells of T. brucei. Sixty percentage of liposome-associated ganglioside GM1-immunized mice survived the infection, and all the mice immunized with bovine brain gangliosides-containing liposomes survived. However, all control mice died within 7 days after infection. These data demonstrate that liposomes containing ganglioside antigens have the potential usefulness for the induction of a protective immune response against T. brucei infection and suggest the possibility of developing vaccines that may ultimately be used for the prevention of trypanosomiasis.     

Mouse virulent strain of Staphylococcus epidermidis. Relation of antiphagocytic activity to the protection-inducing antigen.

Using 10(9) or 10(7) colony-forming units of a strain of Staphylococcus epidermidis (strain 1142) in saline or 5% mucin, respectively, 90 to 100% of mice died within 24 to 48 hr after intraperitoneal challenge infection. These organisms gradually multiplied in the peritoneal cavity when injected intraperitoneally into mice, while the mouse avirulent strain (strain 1124) rapidly decreased and no organisms were found there 20 hr after injection. This strain was capable of inducing resistance against challenge with homologous strains. The resistance appeared as early as the first week and disappeared the 4th week after the immunization. However, no resistance was induced with strain 1124 against challenge with strain 1142. Also, hyperimmune rabbit serum prepared with strain 1142 passively protected against challenge with homologous strain in mice. The protective antibody was absorbed out with homologous organisms but not with strain 1124. Subsequently, a surface substance was obtained from strains 1142 or 1124 by the method of Morse. The 1142 surface substance was capable of inducing a resistance against challenge with the homologous strain but not with the 1124 surface substance. Also, this substance absorbed the protective antibody in hyperimmune rabbit serum prepared with the homologous strain but not with the 1124 surface substance nor with the Smith surface antigen extracted from the Smith strain of Staphylococcus aureus. Conversely, the protective antibody in rabbit anti-Smith strain serum against challenge with the homologous strain was absorbed with the Smith surface antigen but not with the 1142 surface substance. In the agar diffusion test, the 1142 surface substance and the Smith surface antigen produced single precipitin lines only against homologous antisera. Biochemical analysis of the 1142 surface substance showed that the substance contained neither nucleic acids nor proteins but is composed of hexosamine, glycerol, phosphorus, alanine, glycine and phenylalanine.     

Protection and recovery in influenza virus-infected mice immunosuppressed with anti-IgM

BALB/c mice, immunosuppressed from birth with goat anti-mouse IgM, were able to recover from influenza virus infection in the absence of detectable serum and nasal antibody. Recovery was delayed a few days when compared with control animals. Antibody-deficient mice, that had recovered from an initial influenza virus infection, i.e., convalescent mice, were subsequently rechallenged with homologous influenza virus in order to study the importance of nasal and serum antibody in prevention of infection. Convalescent mice were susceptible to reinfection when nasal and serum antibody were not detectable. The mice were resistant to reinfection when serum and/or nasal antibody was detectable by radioimmunoassay. Normal mice that were passively immunized with high titer mouse anti-influenza virus serum were susceptible to challenge with homologous influenza virus. The serum antibody levels in these mice were higher than most of those found in the immune convalescent mice suppressed with anti-IgM, thereby suggesting that the serum antibody, found in convalescent suppressed mice, is not protective. We conclude that 1) mice can recover from influenza virus infection in the absence of detectable levels of nasal and serum antibody, thus indirectly confirming the role of cell-mediated immunity in recovery; 2) serum IgM, IgG2A, IgG2B, IgG3, and probably IgG1 antibody levels are not responsible for protection against influenza virus infection of the upper respiratory tract; and 3) nasal IgA antibody correlates best with protection against reinfection of the upper respiratory tract, but some other locally protective agent cannot be excluded.     

Plasmodium yoelii: characterization of a protective idiotype during malarial infection in mice

We have previously identified and characterized a monoclonal antibody (McAb 302) with potent passive protective activity in mice infected with Plasmodium yoelii, a murine malarial parasite which depends on antibodies for resolution. To further study the appearance and regulation of this antibody during infection, we prepared syngeneic monoclonal antibodies specific for idiotopes present on McAb 302. Three hybridomas were established which synthesized antibodies that bound only to the homologous idiotype but which did not recognize isotypic specificities. All three of these antibodies were found to recognize distinct 302 idiotopes and two of these were shown to be specific for determinants associated with the antibody combining site of McAb 302. One of these monoclonal anti-idiotypic antibodies was used to develop an enzyme-linked immunosorbent assay for the 302 idiotype. When serum samples taken at different times from mice undergoing a primary infection with P. yoelii were tested in this assay, the 302 idiotype could not be detected even though the host was mounting a significant humoral response to the 230-kDa antigen recognized by McAb 302. These studies suggest that the idiotype of the protective McAb 302 is not a predominant one involved in the resolution of a P. yoelii infection and that only some idiotypes of antibodies directed to relevant plasmodial antigens possess significant biological activity. Therefore, protective immunization with plasmodial antigens may require the elicitation of selected idiotypes. Attempts to alter the course of P. yoelii infection by preimmunization with monoclonal or polyclonal anti-idiotypic reagents were unsuccessful.     

Synthesis and Evaluation of a Conjugate Vaccine Composed of Staphylococcus aureus Poly-N-Acetyl-Glucosamine and Clumping Factor A

The increasing frequency, severity and antimicrobial resistance of Staphylococcus aureus infections has made the development of immunotherapies against this pathogen more urgent than ever. Previous immunization attempts using monovalent antigens resulted in at best partial levels of protection against S. aureus infection. We therefore reasoned that synthesizing a bivalent conjugate vaccine composed of two widely expressed antigens of S. aureus would result in additive/synergetic activities by antibodies to each vaccine component and/or in increased strain coverage. For this we used reductive amination, to covalently link the S. aureus antigens clumping factor A (ClfA) and deacetylated poly-N-β-(1-6)-acetyl-glucosamine (dPNAG). Mice immunized with 1, 5 or 10 μg of the dPNAG-ClfA conjugate responded in a dose-dependent manner with IgG to dPNAG and ClfA, whereas mice immunized with a mixture of ClfA and dPNAG developed significantly lower antibody titers to ClfA and no antibodies to PNAG. The dPNAG-ClfA vaccine was also highly immunogenic in rabbits, rhesus monkeys and a goat. Moreover, affinity-purified, antibodies to ClfA from dPNAG-ClfA immune serum blocked the binding of three S. aureus strains to immobilized fibrinogen. In an opsonophagocytic assay (OPKA) goat antibodies to dPNAG-ClfA vaccine, in the presence of complement and polymorphonuclear cells, killed S. aureus Newman and, to a lower extent, S. aureus Newman ΔclfA. A PNAG-negative isogenic mutant was not killed. Moreover, PNAG antigen fully inhibited the killing of S. aureus Newman by antisera to dPNAG-ClfA vaccine. Finally, mice passively vaccinated with goat antisera to dPNAG-ClfA or dPNAG-diphtheria toxoid conjugate had comparable levels of reductions of bacteria in the blood 2 h after infection with three different S. aureus strains as compared to mice given normal goat serum. In conclusion, ClfA is an immunogenic carrier protein that elicited anti-adhesive antibodies that fail to augment the OPK and protective activities of antibodies to the PNAG cell surface polysaccharide.     

Plasmodium chabaudi: Humoral and cell-mediated responses of immunized mice

Antigen preparations of Plasmodium chabaudi parasites enriched in merozoites and schizonts, obtained from in vitro culture, and combined with saponin protected C57BL/6J mice from P. chabaudi infection as judged by reduced primary parasitemias and recrudescences. Sera passively transferred from immunized and untreated mice after a challenge infection were more protective in recipients than serum from normal mice. Mice treated with antilymphocyte serum during immunization did not develop as strong an immunity to infection as did controls treated with normal serum. Immunized mice had depressed delayed-type hypersensitivity reactions to malarial antigen but increased serum titers of malarial antibody (measured by imniunofluorescence) after challenge with P. chabaudi when compared to immunized mice which remained unchallenged. The protective activity of sera from various groups of mice did not necessarily correlate with the serum antibody titers.     

Tamarin model of pneumococcal bacteremia

Tamarins (Saguinus labiatus) were utilized to study host defenses against pneumococcal bacteremia. Tamarins had a poor antibody response to immunization with varying doses of pneumococcal capsular polysaccharide (PCP) vaccine (2 of 15 positive) or to infection with serotype 7F Streptococcus pneumoniae (2 of 14 positive). Tamarins were protected against challenge with a lethal dose of serotype 7F S. pneumoniae if the bacteria were preopsonized with human immune globulin intravenous or if the tamarins were injected with the immune globulin 30 min before challenge. There was minimal protection utilizing a mouse monoclonal anti-type 7F PCP antibody.     

Characterization of Protective Immune Responses Induced by Pneumococcal Surface Protein A in Fusion with Pneumolysin Derivatives

Pneumococcal surface protein A (PspA) and Pneumolysin derivatives (Pds) are important vaccine candidates, which can confer protection in different models of pneumococcal infection. Furthermore, the combination of these two proteins was able to increase protection against pneumococcal sepsis in mice. The present study investigated the potential of hybrid proteins generated by genetic fusion of PspA fragments to Pds to increase cross-protection against fatal pneumococcal infection. Pneumolisoids were fused to the N-terminus of clade 1 or clade 2 pspA gene fragments. Mouse immunization with the fusion proteins induced high levels of antibodies against PspA and Pds, able to bind to intact pneumococci expressing a homologous PspA with the same intensity as antibodies to rPspA alone or the co-administered proteins. However, when antibody binding to pneumococci with heterologous PspAs was examined, antisera to the PspA-Pds fusion molecules showed stronger antibody binding and C3 deposition than antisera to co-administered proteins. In agreement with these results, antisera against the hybrid proteins were more effective in promoting the phagocytosis of bacteria bearing heterologous PspAs in vitro, leading to a significant reduction in the number of bacteria when compared to co-administered proteins. The respective antisera were also capable of neutralizing the lytic activity of Pneumolysin on sheep red blood cells. Finally, mice immunized with fusion proteins were protected against fatal challenge with pneumococcal strains expressing heterologous PspAs. Taken together, the results suggest that PspA-Pd fusion proteins comprise a promising vaccine strategy, able to increase the immune response mediated by cross-reactive antibodies and complement deposition to heterologous strains, and to confer protection against fatal challenge.     

C-reactive protein enhances immunity to Streptococcus pneumoniae by targeting uptake to Fc gamma R on dendritic cells

C-reactive protein (CRP) is an acute phase reactant with roles in innate host defense, clearance of damaged cells, and regulation of the inflammatory response. These activities of CRP depend on ligand recognition, complement activation, and binding to FcgammaR. CRP binds to phosphocholine in the Streptococcus pneumoniae cell wall and provides innate defense against pneumococcal infection. These studies examine the effect of this early innate defense molecule on the development of Abs and protective immunity to S. pneumoniae. Dendritic cells (DC) initiate and direct the adaptive immune response by integrating innate stimuli with cytokine synthesis and Ag presentation. We hypothesized that CRP would direct uptake of S. pneumoniae to FcgammaR on DC and enhance Ag presentation. CRP opsonization of the R36a strain of S. pneumoniae increased the uptake of bacteria by DC. DC pulsed with untreated or CRP-opsonized R36a were transferred into recipient mice, and Ab responses were measured. In mice challenged with free R36a, CRP opsonization resulted in higher secondary and memory IgG responses to both phosphocholine and pneumococcal surface protein A. Furthermore, mice immunized with DC that had been pulsed with CRP-opsonized R36a showed increased resistance to intranasal infection with virulent S. pneumoniae. The effects of CRP on Ag uptake, Ab responses, and protection from infection all required FcR gamma-chain expression on DC. The results indicate that innate recognition by CRP enhances effective uptake and presentation of bacterial Ags through FcgammaR on DC and stimulates protective adaptive immunity.