Age-dependent resistance to Porcine reproductive and respiratory syndrome virus replication in swine.
BACKGROUND
Porcine reproductive and respiratory syndrome virus (PRRSV) causes a prolonged, economically devastating infection in pigs, and immune resistance to infection appears variable. Since the porcine adaptive immune system is not fully competent at birth, we hypothesized that age influences the dynamics of PRRSV infection. Thus, young piglets, growing 16-20-week-old finisher pigs, and mature third parity sows were infected with virulent or attenuated PRRSV, and the dynamics of viral infection, disease, and immune response were monitored over time.


RESULTS
Virulent PRRSV infection and disease were markedly more severe and prolonged in young piglets than in finishers or sows. Attenuated PRRSV in piglets also produced a prolonged viremia that was delayed and reduced in magnitude, and in finishers and sows, about half the animals showed no viremia. Despite marked differences in infection, antibody responses were observed in all animals irrespective of age, with older pigs tending to seroconvert sooner and achieve higher antibody levels than 3-week-old animals. Interferon gamma (IFN gamma) secreting peripheral blood mononuclear cells were more abundant in sows but not specifically increased by PRRSV infection in any age group, and interleukin-10 (IL-10) levels in blood were not correlated with PRRSV infection status.


CONCLUSIONS
These findings show that animal age, perhaps due to increased innate immune resistance, strongly influences the outcome of acute PRRSV infection, whereas an antibody response is triggered at a low threshold of infection that is independent of age. Prolonged infection was not due to IL-10-mediated immunosuppression, and PRRSV did not elicit a specific IFN gamma response, especially in non-adult animals. Equivalent antibody responses were elicited in response to virulent and attenuated viruses, indicating that the antigenic mass necessary for an immune response is produced at a low level of infection, and is not predicted by viremic status. Thus, viral replication was occurring in lung or lymphoid tissues even though viremia was not always observed.
Boehringer Ingelheim Vetmedica Inc, 2501 North Loop Drive, Suite 1000, Ames, IA, 50014, USA. kelly.klinge@boehringer-ingelheim.com
Kelly L
KL
Klinge
Eric M
EM
Vaughn
Michael B
MB
Roof
Elida M
EM
Bautista
Michael P
MP
Murtaugh
D000375:Aging / Q000276:immunology*; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D005260:Female; D007113:Immunity, Innate; D007371:Interferon-gamma / Q000378:metabolism; D016753:Interleukin-10 / Q000097:blood; D007963:Leukocytes, Mononuclear / Q000276:immunology; D008168:Lung / Q000821:virology; D008221:Lymphoid Tissue / Q000821:virology; D008297:Male; D019318:Porcine Reproductive and Respiratory Syndrome / Q000276:immunology* / Q000473:pathology*; D019316:Porcine respiratory and reproductive syndrome virus / Q000276:immunology*; D012720:Severity of Illness Index; D013552:Swine; D019562:Viral Load; D014766:Viremia
D000914:Antibodies, Viral; D016753:Interleukin-10; D007371:Interferon-gamma