The immunogenicity of several cell-wall (CW) fractions was tested in BALB/C mice. These CW fractions were smooth lipopolysaccharide (S-LPS) fraction from smooth (S) strain 16M, sodium dodecyl sulphate-insoluble (SDS-I) CW fraction from strain 16M (S) undigested or digested with pepsin, and SDS-I CW fraction from rough (R) strain H38. The SDS-I CW fraction contained two major outer-membrane proteins (OMPs) of 25-27 kDa and 31-34 kDa, peptidoglycan (PG) and a small quantity (1.5%) of LPS. One month after immunisation, mice were challenged with virulent strain H38 (S) and spleen counts were recorded on days 28 and 49 after challenge. Before challenge, as measured by ELISA, the highest antibody responses to S-LPS were observed in mice immunised with SDS-I CW fraction from strain 16M (S), whether digested with pepsin or undigested. All immunised mice, except those immunised with the SDS-I CW fraction from the R strain, showed higher IgG1 than IgG2a antibody responses to S-LPS (IgG1:IgG2a ratio 3.64-7.71). Antibody responses to the 25-27-kDa OMP were very low, with the highest responses in the mice immunised with the SDS-I CW fraction from the R strain. These results indicated that, in BALB/c mice, these CW fractions probably induced Th2-dependent more than Th1-dependent antibody responses. The highest protection levels were produced by immunisation with the pepsin-digested SDS-I CW fraction from strain 16M (S) and by passive transfer of an anti-S-LPS monoclonal antibody (MAb 2E11; M epitope specificity). S-LPS fraction from strain 16M (S) or SDS-I CW fraction from strain H38 (R) did not induce significant protection. The absence of protection by S-LPS fraction could be explained by the low antibody titres induced by it. On day 49, protection conferred by pepsin-digested SDS-I CW fraction from strain 16M (S) was significantly higher (p < 0.05) than by the untreated SDS-I CW fraction from the corresponding strain. Furthermore, the level of protection in mice immunised with the SDS-I CW fraction from the R strain and which were also passively immunised, 1 day before challenge, with the S-LPS specific MAb was lower than in mice treated with the anti-S-LPS MAb alone. These results indicate that immunity induced by the S strain SDS-I CW fraction is probably mainly S-LPS dependent and that even one or more protein components of this fraction may play an antagonistic role to immunity conferred by S-LPS.


Article metrics loading...

Loading full text...

Full text loading...


Most cited this month Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error