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Immunocompetent BALB/c mice are resistant to infection with Brugia pahangi ( B. pahangi ). In mice treated with a single dose of carrageenan (CGN) or promethazine (PMZ) at an early stage of infection, adult worms and microfilariae were recovered at 12 weeks post-inoculation (PI) with third-stage infective larvae (L3); neither was recovered from control mice. To observe local cellular responses in CGN-treated, PMZ-treated and control mice, we investigated the peritoneal cavities on days 4, 8, 12 and 14 PI. In control mice, larvae were encapsulated by peritoneal exudate cells (PEC) from day 4 PI; morphological observations showed the macrophages and eosinophils were involved with rapid and intense cellular reactions to the larvae. The PEC count was significantly lower in CGN-treated than in control mice on days 8 and 12 PI. The eosinophil content in the PEC of the CGN-treated mice was 0% on days 4, 8 and 12 PI and the larvae were not surrounded by PEC, while it was significantly lower in PMZ-treated mice than in control mice on days 8 and 12 PI; larvae were surrounded by PEC from day 8 PI. The rate of recovery of living larvae was significantly higher in CGN-treated or PMZ-treated mice than in control mice on day 14 PI. These results suggest that the resistance of mice to B. pahangi infection may be determined by early-stage cellular reactions to the larvae; blocking the functions of macrophages and/or eosinophils at this stage may increase susceptibility to infection. |
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