EXPRESSION OF THE SMPA OUTER-MEMBRANE LIPOPROTEIN OF SERPULINA-HYODYSENTERIAE STRAIN P18A IN-VIVO

An ELISA has been developed using a monoclonal antibody (F325 AC4) to the SmpA surface lipoprotein of Serpulina hyodysenteriae strain P18A w hen grown in vitro. The lower level of detection of the ELISA was appr oximately 5 X 10(6) spirochaetes/ml when spirochaetes were either resu spended in phosphate buffered saline or in pig faeces. When pigs were challenged with S. hyodysenteriae strain P18A the lipoprotein was dete cted in the faeces of pigs by ELISA when the numbers of spirochaetes e xcreted was greater than 10(6) per g of faeces. After onset of clinica l signs in the pig, expression of SmpA was not detected by ELISA or by Western blotting using either monoclonal antibody F325 AC4 or polyclo nal antiserum B50 against the SmpA antigen. However, when the in vivo grown spirochaetes were subsequently cultured in vitro expression of S mpA was detected by Western blotting. In the mouse model of swine dyse ntery S. hyodysenteriae spirochaetes obtained from mice with gross les ions also did not express SmpA. It was concluded that the apparent lac k of expression may have been the result of environmental regulation o f gene expression or antigenic variation and was not due to denaturati on of the antigen in vivo.