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Infection and Immunity, May 2005, p. 2986-2990, Vol. 73, No. 5
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.5.2986-2990.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Infection of the Reproductive Tract and Eggs with Salmonella enterica Serovar Pullorum in the Chicken Is Associated with Suppression of Cellular Immunity at Sexual Maturity

Paul Wigley,* Scott. D. Hulme, Claire Powers, Richard K. Beal, Angelo Berchieri Jr., Adrian Smith, and Paul Barrow

Institute for Animal Health, Compton Laboratory, Compton, Newbury, Berkshire RG20 7NN, United Kingdom

Received 14 October 2004/ Returned for modification 15 December 2004/ Accepted 13 January 2005

Salmonella enterica serovar Pullorum causes persistent infections in laying hens. Splenic macrophages are the main site of persistence. At sexual maturity, numbers of bacteria increase and spread to the reproductive tract, which may result in vertical transmission to eggs or chicks. In this study we demonstrate that both male and female chickens may develop a carrier state following infection but that the increases in bacterial numbers and spread to the reproductive tract are phenomena restricted to hens, indicating that such changes are likely to be related to the onset of egg laying. The immunological responses during the carrier state and through the onset of laying in hens were determined. These indicate that chickens produce both humoral and T-cell responses to infection, but at the onset of laying both the T-cell response to Salmonella and nonspecific responses to mitogenic stimulation fall sharply in both infected and noninfected birds. The fall in T-cell responsiveness coincided with the increase in numbers of Salmonella serovar Pullorum and its spread to the reproductive tract. Three weeks after the onset of egg laying, T-cell responsiveness began to increase and bacterial numbers declined. Specific antibody levels changed little at the onset of laying but increased following the rise in bacterial numbers in a manner reminiscent of a secondary antibody response to rechallenge. These findings indicate that a nonspecific suppression of cellular responses occurs at the onset of laying and plays a major role the ability of Salmonella serovar Pullorum to infect the reproductive tract, leading to transmission to eggs. The loss of T-cell activity at the point of laying also has implications for Salmonella enterica serovar Enteritidis infection and transmission to eggs, along with its control by vaccination offering a "window of opportunity" in which infection may occur.

* Corresponding author. Present address: Department of Veterinary Pathology, Faculty of Veterinary Science, University of Liverpool, Leahurst, Neston CH64 7TE, United Kingdom. Phone: 44 151 794 6193. Fax.: 44 151 795 6005. E-mail: Paul.Wigley{at}liverpool.ac.uk.

Editor: A. D. O'Brien

Infection and Immunity, May 2005, p. 2986-2990, Vol. 73, No. 5
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.5.2986-2990.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.





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