Characterization of immunosuppressive proteins of Brugia malayi microfilariae.

Inhibition of Concanavalin A-induced lymphocyte proliferation was used to monitor the partial purification and characterization of suppressor molecules from microfilariae of Brugia malayi. Suppressor activity was present in high molecular weight fractions of microfilarial extracts (Mr greater than 50 kd on SDS-PAGE) and was protease-sensitive but resisted treatment with sodium periodate, indicating that it is associated with parasite proteins. Suppressor activity was released by microfilariae cultured in vitro and could be detected in peritoneal exudates of intraperitoneally-infected jirds and in lymph and sera from athymic C3H/HeN mice with patent B. malayi infections. These findings indicate that immune unresponsiveness during patent filarial infections may result from the in vivo release by microfilariae of high molecular weight proteins that suppress host immune responses.