Neonatal sex steroids affect responses to Seoul virus infection in male but not female Norway rats

Previous studies illustrate that after inoculation with Seoul virus (i.e., the naturally occurring hantavirus found in Norway rats), adult male rats produce higher antibody responses, exhibit higher Th1 responses (i.e., IgG2a, IL-2, and IFNγ), and shed virus longer than females, but these difference are not altered by manipulation of sex steroids in adulthood. To determine whether sex steroid hormones organize adult responses to hantavirus infection, at 2–4 days of age, male rats were gonadectomized and female rats were injected with testosterone. As adults, animals were inoculated with 10 4pfu of Seoul virus. Neonatally gonadectomized males (NGM), control females (CF), and neonatal testosterone-treated females (NTF) had lower anti-Seoul virus IgG and IgG2a responses than control males (CM) 20, 30, and 40 days post-inoculation. Neonatal testosterone treatment had no effect on female antibody responses to infection. NGM, CF, and NTF shed virus in saliva and feces for a shorter duration than CM. There was no effect of neonatal hormone manipulation either on the percentage of animals with detectable virus or on the number of virus copies within each target organ. Genetic males, regardless of hormone manipulation, had higher virus replication in lung tissue than did genetic females. Neonatal sex steroids influence the sexual dimorphism in host immune function but do not modify virus replication in target tissues.