Fig. 3.

Breast milk collected from latent mothers was sufficient to transfer MCMV infection to neonatal mice. (A) Female C57BL/6 mice were infected with 30,000 PFU of MCMV; after 16 weeks, when MCMV is latent, mice were bred. Twelve days after the birth of the litter, leukocytes were collected from breast milk or blood from two nursing mothers. Total RNA was analyzed for evidence of reactivation of latent MCMV during lactation by determining MCMV IE-1 gene expression by RT-PCR with Southern analysis. The same RNA preparations were analyzed for expression of the reference gene GAPDH by RT-PCR. (B) Thirteen to 14 days after the birth of their litters, 3 latent mothers, infected with 3,000 PFU of MCMV Smith, were anesthetized and treated with 2 IU of oxytocin. Total volumes of 80 μl, 150 μl, and 150 μl of breast milk were collected from latent mothers A, B, and C, respectively. Each milk sample was diluted 1:2 in sterile DPBS and injected (i.p.) into two 6-day-old CD-1 pups. Seven days after injection, pups were sacrificed and total RNA was prepared from brain, liver, lung, spleen, kidney, and salivary glands from individual pups and examined for MCMV IE-1 gene expression by RT-PCR with Southern analysis. It was interesting that MCMV IE-1 mRNA was not detected in the brain or kidney of neonates infected with breast milk via the i.p. route.