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Active immunity and maternally transmitted passive immunity to respiratory syncytial virus (RSV) were studied in cotton rats. Animals infected with respiratory syncytial virus developed complete resistance to pulmonary reinfection, which lasted at least 18 months. Nasal resistance was of shorter duration and began to diminish in 8 months. Pulmonary resistance was transferred by parabiosis, but nasal resistance was not. Adoptive transfer studies with fractionated convalescent blood showed that serum antibody, but not circulating lymphocytes, conferred pulmonary resistance. Immune females conferred antibody to their young prenatally and postnatally, with most of the antibody being transferred via colostrum and milk. Maternally transmitted immunity was more effective in the lungs than in the nose and was transient in both organs. Foster nursing experiments showed colostrum and milk to be the most important routes of immune transfer. Although resistance in infants generally correlated with serum neutralizing antibody levels, several exceptions to this correlation suggested that immune factors other than neutralizing antibody may also play an important role in maternal passive immunity.

The cotton rat Sigmodon hispidus has provided an animal model of adenovirus pneumonia that permits investigation of the viral gene products required to produce the disease and the molecular mechanisms effecting the damage. This study was One utility of the modern techniques of virology and molecular biology should be to reveal the basic molecular mechanisms by which viruses such as adenoviruses produce disease. The discovery that intranasal inoculation of type 5 adenovirus (AdS) into cotton rats results in development of a pneumonia that pathologically simulates that produced in humans (1) provided the opportunity to determine the viral gene functions required to produce the pneumonia and the molecular mechanisms by which the virus induced the disease. Extensive studies have been carried out on the replication of adenovirus in the lungs of the Sigmodon hispidus species of cotton rats and on the relationship of viral multiplication to the development of pneumonia (2, 3). Productive viral replication was only detected in the epithelial cells of the bronchi and bronchioles of the lung and the nasal mucosa. Onset of viral multiplication, which reached maximum titers 2-4 days after infection (depending upon the size of the inoculum), was soon followed by progressively increasing peribronchial, perivascular, and alveolar septal infiltration of lymphocytes and monocyte/macrophages and finally by lymphocytic infiltration of the basal bronchiolar wall into the epithelium; scattered polymorphonuclear leukocytes (PMN) were also present (2, 3). The maximum pathology was attained 5-7 days after infection, which was also dependent upon the viral inoculum. The use of conditionally lethal, temperature-sensitive mutants [e.g., H5ts125 (4)] unable to replicate their DNA at the cotton rat's normal body temperature, about 39.2°C, led to unexpected results: the cellular inflammatory response was the same as in wild-type (Wt) virus-infected lungs, although quantitatively not as extensive. These data indicate that only early gene products appear necessary to induce the inflammatory response to viral infection. It was further demonstrated that the E1B 58-kDa protein, which is required to shut off host protein synthesis during adenovirus productive infection (5, 6), is also essential for producing maximum viral pneumonia (3).Early region 3 (E3) has been termed a "nonessential" region since naturally occurring mutants or hybrid viruses in which almost the entire region is deleted still replicate like Wt virus in cultured cells (7). It seemed unlikely that almost 10% of the genome would have survived in evolution if its encoded genes did not play a significant role in the virus's life cycle. Therefore, extensive studies were done to determine whether the E3 region might play a critical role in pathogenesis. It is the objective of this communication to report the results of that investigation. Data will be presented to show that gene products of the E3 region do in fact play a strategic role in viral pathogenesis. However, their ...

Cotton rats previously inoculated with Formalin-inactivated respiratory syncytial virus (RSV) were challenged intranasally with live RSV to induce an enhancement of RSV disease similar to that observed after the administration of Formalin-inactivated RSV vaccine to human infants 20 years ago. Within 24 h after infection with RSV, cotton rats developed pulmonary lesions that reached a maximum by day 4. Histologically, the lesions resembled an experimental pulmonary Arthus reaction. An action of Formalin on RSV appears to be responsible for this effect, because live virus or virus heated in the absence of Formalin did not induce enhanced immunopathology. Selected epitopes on the fusion (F) or attachment (G) or both RSV surface glycoproteins that are involved in inducing neutralizing antibodies were modified to reduce or ablate their antigenicity. However, other epitopes on the F or G or both glycoproteins were not ablated by Formalin, because cotton rats inoculated parenterally with a Formalin-inactivated virus developed a high level of F and G antibodies measurable by an enzyme-linked immunosorbent assay. At this time, the effect of Formalin on RSV cannot be localized to either the F or G glycoprotein of RSV.

The amount of passively acquired serum respiratory syncytial virus (RSV)-neutralizing antibodies required to protect the respiratory tract of cotton rats against infection was studied. Infant cotton rats were inoculated intraperitoneally with various dilutions of a single pool of sera derived from cotton rats convalescent from RSV infection. After 24 h, these animals were inoculated with RSV intranasally. Virus replication in the respiratory tract was suppressed in cotton rats which had a serum neutralizing antibody titer of 1:100 or greater. Resistance was greater in the lungs than in the nose. Complete or almost complete resistance in the lungs was observed in cotton rats with a serum neutralizing antibody titer of 1:380 or greater. The level of serum RSV-neutralizing antibodies required to confer signfficant resistance to infection in the cotton rat was similar to the level of maternally derived serum antibodies possessed by human infants less than 2 months of age, who as a group exhibit relative resistance to RSV disease compared with infants 2 to 6 months of age.

Respiratory syncytial virus infected the nose and lungs of each of 20 strains of inbred mice, with viral titers varying 100-fold from least permissive to most permissive strains. Viral titers appeared to be under genetic control, but did not correlate with the H-2 haplotype.

Cotton rats (Sigmodon hispidus) were inoculated intranasally with 102.0 to 1010.0 PFU of human adenovirus type 5. The virus replicated to a high titer in pulmonary tissues, with the peak titer being proportional to the input dose. The 50% lethal dose was 109-4 PFU. Histopathologic changes were proportional to the infecting inoculum and included the infiltration of interstitial and intra-alveolar areas, moderate damage to bronchiolar epithelium, and cellular infiltration of peribronchiolar and perivascular regions. These changes could be divided into two phases: an early phase (affecting alveoli, bronchiolar epithelium, and peribronchiolar regions) with an infiltrate consisting primarily of monocytes-macrophages and neutrophils, with occasional lymphocytes, and a later phase (affecting peribronchiolar and perivascular regions) with an infiltrate consisting almost exclusively of lymphocytes. In both phases, the predominant process was the response of the host to infection, rather than direct viral damage to infected cells. An infecting inoculum of 108.0 PFU or larger caused severe damage to type II alveolar cells, which were swollen, showed a loss of lamellar bodies, and were surrounded by polymorphonuclear leukocytes and macrophages. No evidence of complete viral replication was found in type II alveolar cells.

Intranasal inoculation of type 5 adenovirus into the cotton rat Sigmodon hispidus produces a pneumonia pathologically similar to that in humans, and it, therefore, provides an excellent animal model to investigate the pathogenesis of this disease. The goal of this study was to test the hypothesis that accumulation of viral structural proteins is responsible for a major portion of the cell-damage-producing disease. Since viral DNA replication is essential for synthesis of the viral structural proteins, which are products of late genes, the hypothesis was tested using mutants defective in genes required for DNA synthesis. Most experiments were done with the conditionally lethal temperature-sensitive (ts) mutant H5ts125, which contains a mutation in the early region 2A When cotton rats were infected with 1 x 1080-plaque-forming units of wild-type adenovirus type 5 or HMts125, the pneumonias that followed were pathologically similar; in the latter phases, however, wild-type virus produced slightly more extensive pneumonia than did HSts125, probably because its replication permitted infection of more susceptible cells.The discovery of adenoviruses (1, 2), an important human pathogen whose 42 viral types produce a variety of diseases, led to extensive studies into the virion structure, the viral structural proteins, the nature of the viral genome, and the biochemical and molecular events in the sequential biosynthesis of the viral gene products (3). During type 5 adenovirus (Ad5) replication, host cell DNA synthesis is completely blocked about 12 hr after infection with AdS (4, 5), and host RNA and protein syntheses are blocked about 18-20 hr after infection (5-7). In addition, only about 10% of the viral DNA and structural proteins synthesized are actually packaged into mature virions whereas the remainder accumulate in the nuclei ofinfected cells forming inclusion bodies (8-11). These findings led to the hypothesis that the combination of shut-off of biosynthesis of host macromolecules and the intranuclear accumulation of large amounts of viral DNA and structural proteins leads to cell death and production of disease (5). Indeed, the purified fiber protein inhibited viral multiplication when added to adenovirus-infected KB cells, and it was shown to inhibit incorporation of [3H]thymidine into cellular DNA in cell extracts in vitro (12, 13).The objective of the study to be described was to test the hypothesis that production of an excess of late viral proteins is responsible for the molecular events essential for the pathogenesis of adenovirus disease. Thus, if synthesis of the late structural proteins were blocked, disease should not develop. This possibility was readily tested since mutants unable to synthesize viral DNA cannot produce late structural proteins, and such mutants had been isolated (14). H5ts125 (14) and H5ts149 (15) are conditionally lethal temperature-sensitive (ts) mutants that cannot replicate their DNA at their nonpermissive temperature of 39.50C, which fortunately is close to the body te...