Severe acute respiratory syndrome (SARS) is a disease characterized by diffuse alveolar damage. We isolated human alveolar type II cells and maintained them in a highly differentiated state. Type II cell cultures supported SARS-CoV replication as evidenced by RT-PCR detection of viral subgenomic RNA and an increase in virus titer. Virus titers were maximal by 24 h and peaked at approximately 10(5) pfu/mL. Two cell types within the cultures were infected. One cell type was type II cells, which were positive for SP-A, SP-C, cytokeratin, a type II cell-specific monoclonal antibody, and Ep-CAM. The other cell type was composed of spindle-shaped cells that were positive for vimentin and collagen III and likely fibroblasts. Viral replication was not detected in type I-like cells or macrophages. Hence, differentiated adult human alveolar type II cells were infectible but alveolar type I-like cells and alveolar macrophages did not support productive infection.

Saliva of arthropod vectors can modulate vertebrate host immunological functions in many ways. To investigate if vesicular stomatitis New Jersey virus (VSNJ) infection could be potentiated by arthropod saliva, mice in three different age groups (3 days, 3 weeks, or > 8 months) were exposed to VSNJ-infected mosquitoes or were needle injected with an equivalent dose of VSNJ (titre 1.5-3 logs). Previous studies have demonstrated that VS viruses do not replicate in mice older than 3 weeks of age. Infection was monitored by examining serum for the presence of VSNJ at 2 days postinfection (PI) or for neutralizing antibody on days 7 and 14 PI. All 3-day-old mice succumbed to viral infection by mosquito transmission or delivery by injection. Ninety-four percent of the 3-week-old mice bitten by infected mosquitoes developed antibody, whereas antibody was detected in only 13% of inoculated mice. Adult mice developed neutralizing antibody (73%) when fed upon by infected mosquitoes, but only 11% developed antibody when virus was injected. Day 2 serum samples from 3-week and adult age groups were negative by virus isolation. These data indicate that mosquito mediated delivery of VSNJ exacerbates virus infection in mice older than 3 weeks.

Electron microscopy of zoocin A-treated sensitive streptococcus cells revealed cytoplasmic disruption and ultimately complete rupture of the cell wall. Culture viability and optical density were shown to decrease rapidly and simultaneously in Streptococcus pyogenes FF22 but less quickly in the relatively more resistant Streptococcus mutans 10449. Zoocin A was shown to cleave hexaglycine in a colorimetric cell-free microtiter assay system, and it is concluded that the killing action of zoocin A, like that of lysostaphin, is most probably the result of direct cleavage of the peptidoglycan cross-links in the cell wall. The relationship between sensitivity to zoocin A and the peptidoglycan cross-linkage structure of Streptococcus zooepidemicus, Lactococcus spp., S. pyogenes, Streptococcus gordonii, Streptococcus oralis, S. mutans, and Streptococcus rattus has been evaluated.

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To better define the relationship between ovine lentivirus (OvLV) infection and respiratory disease, pulmonary leukocytes and postmortem lung specimens from 42 sheep seropositive or at risk for OvLV infection were obtained. The lungs were examined for lesions of lymphoid interstitial pneumonia (LIP), and animals were categorized into five groups by severity of LIP and OvLV serologic status. The presence of OvLV in alveolar macrophages was established by proviral DNA amplification using the polymerase chain reaction (PCR), and the proportion of infected cells was determined by a quantitative focal immunoassay (FIA) and by immunohistochemistry. The concentration of OvLV p25 in serum was measured by capture ELISA. In contrast to animals with mild or no pulmonary lesions, sheep with moderate or severe LIP (17/42) were all seropositive, 71% had antigenemia (greater than 2 ng/mL), and 82% had proviral DNA in 1.5 x 10(5) alveolar macrophages. Of sheep positive by PCR, those with moderate or severe LIP (79%) had an average of 3 infected cells/10(3) alveolar macrophages by FIA. These results implicate alveolar macrophages as important target cells in the pathogenesis of OvLV-induced respiratory diseases.