Group B streptococcal lung infection in neonatal rabbits.
The interaction of alveolar macrophages (AMs) and group B streptococci (GBS) was investigated in 1 and 2-day-old rabbits following infection in an exposure chamber containing 10(7) streptococci per cubic foot of air. The % of streptococci within AMs was similar at 0 and 4 h (36 and 65%) after infection for the two groups of rabbits. Twenty-four h after infection, the 2-day-old rabbits had a significantly higher % of ingested GBS (86 versus 68%). Sixty % of inspired GBS were inactivated by the older rabbits within 4 h after infection. This clearance persisted in the younger rabbits until 48 h (mean negative clearance of -17, -276, and -79% at 4, 24, and 48 h) before their numbers were reduced by inflammation. Sixty of 78 1-day-old rabbits had inflammatory responses between 24 and 72 h versus only 5 of 50 older rabbits. At 24 h after infection, AMs of 1-day-old rabbits contained significantly increased numbers of intracellular GBS microcolonies (17/20) than did AMs from 2-day-old rabbits (5/19). These observations suggest that the enhanced susceptibility to GBS infection in the immediate postnatal period is caused at least in part by ineffective intracellular killing by AMs.
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn / Q000276:immunology*; D008168:Lung / Q000473:pathology; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism / Q000502:physiology; D011014:Pneumonia / Q000276:immunology*; D011817:Rabbits; D013290:Streptococcal Infections / Q000276:immunology*; D013292:Streptococcus agalactiae / Q000254:growth & development / Q000276:immunology*