Shigella dysenteriae type 1 causes devastating epidemics in
developing countries with high case-fatality rates in all age-groups.
The aim of the study was to compare host immune responses to epidemic
(T2218) and endemic strains of S. dysenteriae type 1. Shigellacidal
activity of serum from rabbits immunized with epidemic or endemic
strains, S. dysenteriae type 1-infected patients, and healthy adult
controls from Shigellaendemic and non-endemic regions was measured.
Immunogenic cross-reactivity of antibodies against Shigella antigens
was evaluated by Western blot analysis. Oxidative burst and phagocytic
responses of monocytes and neutrophils to selected S. dysenteriae type
1 strains were assessed by flow cytometry. Rabbit antisera against
epidemic strain were less effective in killing heterologous bacteria
compared to endemic antisera (p=0.0002). Patients showed an increased
serum shigellacidal response after two weeks of onset of diarrhoea
compared to the acute stage (3-4 days after onset) against their
respective homologous strains; the response against T2218 and
heterologous endemic S. dysenteriae type 1 strains was not significant.
The serum shigellacidal response against all the S. dysenteriae type 1
strains was similar among healthy controls from endemic and non-endemic
regions and was comparable with the acute stage response by patients.
Compared to endemic strains of S. dysenteriae type 1, T2218 was
significantly resistant to phagocytosis by both monocytes and
neutrophils. No obvious differences were obtained in the induction of
oxidative burst activity and cathelicidin-mediated killing.
Cross-reactivity of antibody against antigens present in the epidemic
and endemic strains showed some differences in protein/peptide
complexity and intensity by Western blot analysis. In summary, epidemic
T2218 strain was more resistant to antibody-mediated defenses, namely
phagocytosis and shigellacidal activity, compared to endemic S.
dysenteriae type 1 strains. Part of this variation may be attributed to
the differential complexity of protein/peptide antigens