Clearance of Brugia pahangi microfilariae in immunized mice

Active Brugia pahangi microfilariae (Mf) were injected into naive male BALB/c mice intraperitoneally. Microfilaraemia was studied for 28 days; and Mf circulated in blood in optimum numbers from 3 to 14 days. Anti-Mf response was assessed by the rate of disappearance of Mf from blood as well as their absence from visceral organs. Sonicated antigens of Mf (MfE) and whole worm extract of adults (WWE) induced absolute protection against the establishment of Mf in mice. This potent anti-Mf response elicited by sonicated antigens was intense, rapid and withstood repeated challenge infection. In comparison, immunization with in vitro excretory, secretory and metabolic antigens of Mf (MfESM) produced a partial but significant level of protection. Sera collected periodically from immunized animals showed antibody by micro-ELISA compared to sham-vaccinated controls. When Mf were used as targets along with the peritoneal exudate cells in vitro, sera from mice immunized with MfE and MfESM showed about four-fold cellular adherence to (Mf-ADCA) and 10-fold killing (Mf-ADCC) of Mf which was antibody-dependent. Some degree of correlation was apparent when the antibody levels, Mf-ADCA/Mf-ADCC activity, and Mf clearance were compared. This murine microfilaraemia model was therefore shown to be suitable for studying the host-protective immune response against filarial parasites.