SUSCEPTIBILITY TO PNEUMOCYSTIS-CARINII INFECTION - HOST RESPONSES OF NEONATAL MICE FROM IMMUNE OR NAIVE MOTHERS AND OF IMMUNE OR NAIVE ADULTS

Mice from either naive or immunized dams were given intranasal inocula tions of Pneumocystis carinii as neonates (24 to 48 hold), Lung P. car inii burdens increased through day 13 postinoculation in all pups and declined to nearly undetectable numbers by day 23 in pups from immune mothers, However, P. carinii numbers in pups from naive mothers did no t begin to decline significantly until after day 33, and P. carinii or ganisms were still detectable in low numbers through day 45, In contra st, the lungs of naive or immunized adult mice contained detectable nu mbers of P. carinii organisms only up to 9 or 3 days, respectively, af ter inoculation, The onset of clearance of P. carinii organisms from t he lungs of neonatal mice and naive adults was coincident with infiltr ation of neutrophils and CD4(+) CD45RB(lo) cells into the alveolar spa ces and increased titers of P. carinii-specific antibody in sera, Immu nized dams had high levels of P. carinii-specific antibody in both the ir sera and milk, and pups from these dams had higher titers of P. car inii-specific antibody than did pups from naive dams, These data indic ate that P. carinii survives for a much longer period in neonates than in adult mice, which is the result of a delay in the onset of the imm une response in neonates. Furthermore, immunized mothers contributed t o an early clearance of P. carinii organisms by their offspring presum ably because of the transfer of P. carinii-specific antibody. However, the passively acquired antibody did not seem to have an effect until the neonates began to mount their own responses.