A 10-kDa structural protein of porcine reproductive and respiratory syndrome virus encoded by ORF2b.

The major structural proteins of porcine reproductive and respiratory syndrome virus (PRRSV) are derived from ORFs 5, 6, and 7. Western blots of sucrose gradient-purified virions and PRRSV-infected MARC-145 cells, probed with immune pig serum, showed the presence of an additional 10-kDa protein. Nucleotide sequence analysis of North American PRRSV isolate SDSU-23983 revealed a small ORF within ORF2, named ORF2b, which, when translated, produced a 73-amino-acid nonglycosylated protein. Recombinant 2b protein expressed by a baculovirus clone, AcVR2, comigrated with the 10-kDa virus-associated protein. The loss of 10-kDa protein immunoreactivity after absorption of immune sera with lysates from AcVR2-infected insect cells demonstrated that the 2b and 10-kDa proteins are immunologically similar. Immunoblots were also used for the detection of anti-2b activity in serum samples from experimentally infected adult pigs. Antibodies against PRRSV were apparent by 14 days postinfection, followed by anti-2b activity and serum neutralizing activity. The putative ORF2b start codon is only 6 nucleotides downstream of the adenine of the ORF2a start codon. The expression of ORF2a and 2b as enhanced green fluorescent fusion proteins showed that both proteins were translated; however, the ORF2b was preferentially expressed. These results suggest that the 2b protein is virion associated and the principal product of ORF2.

Age-dependent poliomyelitis in mice is associated with respiratory failure and viral replication in the central nervous system and lung.

Age-dependent poliomyelitis (ADPM) is a virally induced neuroparalytic disease of mice and a model for amyotrophic lateral sclerosis (ALS). ADPM is triggered in genetically susceptible mice by immunosuppression and infection with lactate dehydrogenase-elevating virus (LDV). Both ADPM and ALS are characterized by progressive degeneration of anterior horn motor neurons, and death in ALS is usually associated with respiratory failure. To assess respiratory function in ADPM, we investigated ventilation in conscious control and LDV-infected C58/J mice breathing air and then 6.5% CO(2) in O(2). Three days after LDV infection, ventilation in response to CO(2) was half of that compared to the uninfected state, but become normalized by 10 days. Administration of cyclophosphamide alone (200 mg/kg, ip), an immunosuppressant, had no effect on ventilation. Induction of ADPM by concomitant administration of LDV to cyclophosphamide-treated mice resulted in altered gait, hindlimb paralysis, wasting, decreased metabolism, and decreased body temperature by 4 degrees C relative to controls. Compared to baseline values, mice with ADPM had decreased tidal volume and ventilation while breathing air, and while exposed to the CO(2) challenge they were unable to increase tidal volume, frequency of breathing, or ventilation. Using in situ hybridization, LDV replication was noted within the spinal cord, brain, and lung, but not in the diaphragm. Thus, respiratory failure is a contributory mechanism leading to death in ADPM and is associated with LDV replication in the CNS and lung. This animal model may be useful to investigate physiological and molecular mechanisms associated with the development of respiratory failure in neurodegenerative diseases.