Humoral immune response in chinchillas to the capsular polysaccharides of Streptococcus pneumoniae

Otitis media: the chinchilla model

Streptococcus pneumoniae infection and disease have been modeled in several animal species including infant and adult mice, infant and adult rats, infant Rhesus monkeys, and adolescent and adult chinchillas. Most are models of sepsis arising from intravenous or intraperitoneal inoculation of bacteria, and a few were designed to study disease arising from intranasal infection. Chinchillas provide the only animal model of middle ear pneumococcal infection in which the disease can be produced by very small inocula injected into the middle ear (ME) or intranasally, and in which the disease remains localized to the ME in most cases. This model, developed at the University of Minnesota in 1975, has been used to study pneumococcal pathogenesis at a mucosal site, immunogenicity and efficacy of pneumococcal capsular polysaccharide (PS) vaccine antigens, and the kinetics and efficacy of antimicrobial drugs. Pathogenesis experiments in the chinchilla model have revealed variation in ME virulence among different pneumococcal serotypes, enhancement of ME infection during concurrent intranasal influenza A virus infections, and natural resolution of pneumococcal otitis media (OM) without intervention. Research has explored the relative contribution of pneumococcal and host products to ME inflammation. Pneumococcal cell wall components and pneumolysin have been studied in the model. Host inflammatory responses studied in the chinchilla ME include polymorphonuclear leukocyte oxidative products, hydrolytic enzymes, cytokine and eicosanoid metabolites, and ME epithelial cell adhesion and mucous glycoprotein production. Both clinical (tympanic membrane appearance) and histopathology (ME, Eustachian tube, inner ear) endpoints can be quantified. Immunologic and inflammatory studies have been facilitated by the production of affinity-purified antichinchilla immunoglobulin G (IgG), IgM, and secretory IgA polyclonal antibody reagents, and the identification of cross-reactivity between human and chinchilla cytokines, and between guinea pig and chinchilla C3. Alteration of ME mucosa by pneumococcal neuraminidase and alteration of ME epithelial cell (MEEC) surface carbohydrates during intranasal pneumococcal infection have been demonstrated. Pathogenesis studies have been aided by cultured chinchilla MEEC systems, in which the ability of platelet activating factor and interleukin (IL)-1 beta to stimulate epithelial mucous glycoprotein synthesis has recently been demonstrated. Because chronic OM with effusion is characterized by presence of large amounts of mucous glycoprotein in the ME, pneumococcus may have an important role in both acute and chronic ME disease. Both unconjugated PS and PS-protein-conjugated vaccines are immunogenic after intramuscular administration without adjuvant in chinchillas. Passive protection studies with human hyperimmune immunoglobulin demonstrated that anti-PS IgG alone is capable of protecting the chinchilla ME from direct ME challenge with pneumococci. Active PS immunization studies demonstrated protection following direct ME and intranasal pneumococcal challenge with and without concurrent influenza A virus infection. An attenuated influenza A virus vaccine also showed protection for pneumococcal OM. Antimicrobial treatment of acute OM has been based almost exclusively on empirical drug use and clinical trials without a foundation of ME pharmacokinetics. Studies in the chinchilla model have started to bring a rational basis to drug selection and dosing. Microassays have been developed using high-pressure liquid chromatography for many relevant drugs. Studies have explored the in vivo ME response in pneumococcal OM to antimicrobial drugs at supra- and sub-minimum inhibitory concentration (MIC), the effect of concurrent influenza A virus infection on ME drug penetration, and the effect of treatment on sensorineural hearing loss produced by pneumococcal OM.

Enzyme immunoassay for detection of immunoglobulin G (IgG), IgM, and IgA antibodies against type 6B pneumococcal capsular polysaccharide and cell wall C polysaccharide in chinchilla serum

Conjugation of the capsular polysaccharides of Streptococcus pneumoniae to protein carriers has introduced a new generation of pneumococcal vaccines which may be efficacious in preventing pneumococcal otitis media during infancy. The chinchilla model has been used extensively for studying the pathogenesis of pneumococcal otitis media and for testing the efficacy of early pneumococcal capsular polysaccharide (PCP) vaccines, but immunologic studies in the chinchilla have been limited by the lack of antibodies against specific immunoglobulin isotypes. By using affinity-purified rabbit immunoglobulin G (IgG) anti-chinchilla IgG, IgM, and IgA, we developed a sensitive enzyme immunoassay that is highly specific for IgG, IgM, and IgA antibodies against type 6B PCP (anti-6B) and against C polysaccharide in chinchilla serum. Antibody titers increased in serum from five chinchillas immunized with a type 6B outer membrane protein complex vaccine. Increases of anti-6B IgG and IgM antibody titers were more striking than increases of anti-6B IgA or anti-C polysaccharide IgG, IgM, or IgA titers were.

Immunoprophylaxis of otitis media

Prospects for an effective otitis media vaccine are bolstered by a number of encouraging observations. Results of pneumococcal polysaccharide vaccine trials beginning in 1975, the enormously enhanced immunogenicity of protein-Hib polysaccharide coupled vaccines in infants, and the apparent effectiveness of a protein-PCP coupled vaccine in experimental otitis media suggest that a pneumococcal vaccine targeted to prevent invasive and middle ear infections is not too distant. The identification of several conserved surface antigens on NTHi and demonstration of otitis media protection elicited by these antigens in an animal model give promise for the development of H. influenzae vaccines for otitis media. Evidence that attenuated influenza A virus vaccination may also be an effective strategy for otitis media prevention, at least in an animal model, suggests that priority should be given to testing the efficacy of influenza, parainfluenza and respiratory syncytial virus vaccines with respect to otitis media prevention. It seems quite likely that not one but several immunoprophylaxis approaches will be necessary to reduce the overall incidence of otitis media given the multifactorial nature of the disease. Increasing parent and physician concern with the high incidence of otitis media and its morbidity suggests high participation rates in vaccine trials and high utilization of vaccines shown to be protective. Even if a vaccine could reduce the incidence of otitis media by 30%, an annual health care savings of $300-750 million would be achieved.

Historical perspectives and concepts in otitis media research at the University of Minnesota

The University of Minnesota Otitis Media Research Center, formed in 1978, comprises a multidisciplinary research team in the clinical fields of otolaryngology, pediatrics, audiology, and infectious disease as well as the basic science fields of histopathology, epidemiology, microbiology, immunology, biostatistics, pharmacology, physiology, and biochemistry. The team has focused on studies designed to elucidate the pathophysiology of the otitis media continuum, and considerable progress has been made in describing this continuum by using the basic science approaches available in the Center. The collaboration of basic and clinical scientists has created a synergy of goals, ideas, and methods leading to new hypotheses and progress, ultimately resulting in improved patient care methods.