The class and subclass distribution of antibody response to the culture ®ltrate antigen (CFA) of Burkholderia pseudomallei was examined in the sera of 45 septicaemic and 17 localised melioidosis cases and 40 cases clinically suspected of melioidosis and the results were compared with those from high-risk and healthy control groups. The geometric mean titre index (GMTI) values for all classes and subclasses of immunoglobulins examined were higher for sera from the proven and clinically suspected melioidosis cases than for the control groups. However, the highest response in the three patient groups was that of IgG with GMTIs ranging from 219.4 to 291.6 and the lowest was for IgM with GMTIs of 22.5, 24.3 and 28.7. The IgA response was intermediate with GMTIs ranging from 119.2 to 170. The GMTIs were highest for IgG in septicaemic and localised infections and for IgA and IgM in localised infections. As regards IgG subclass distribution, IgG1 and IgG2 were the predominant subclasses produced against the CFA in contrast to IgG3 and IgG4, which were produced in low amounts. None of the sera from the control groups had any signi®cant titres of antibodies.
A 120 kDa antigen containing SDS-PAGE fraction BmA-2 isolated from Brugia malayi adult parasite was highly reactive with normal sera from filarial endemic area. BmA-2 was analysed for its prophylactic potential in in vitro and in vivo. Sera collected from BmA-2 immunized jirds induced a significant level (80 to 90%) of protection against infective larvae and microfilariae in in vitro ADCC assay as well as in in situ micropore chamber implantation studies. Mastomys natalensis immunized with BmA-2 showed a significant level of protective response against circulating microfilariae by clearing 90% of them from circulation by fifth day after challenge infection. Immunization of jirds with BmA-2 resulted in an enhanced level of antibody response against BmA-2 and 88% reduction in the development of the parasites to the adult stage. Passive transfer of immunesera from jirds immunized with BmA-2 to naive jirds resulted in 71% reduction in adult worm recovery as observed 90 days after challenge infection with B. malayi. On the other hand the passive transfer of non-adherent spleen cells from immune jirds did not show any significant effect on the development of parasite. Administration of jirds anti BmA-2 serum to microfilaraemic jirds showed a temporary decrease in microfilarial count which was increased to pretherapeutic level within 100 days and there was no effect on the adult worms. This implies that the immune protective effect of BmA-2 is mainly antibody dependent and active immunization with BmA-2 is effective against filarial infection.
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