Inhibition of antigen-driven proliferative responses and enhancement of antibody production during infection with Brugia pahangi

Long standing Brugia pahangi infections in seven dogs, restricted to one rear limb popliteal lymph node and its afferent ducts, were monitored with regard to proliferative responses and antibody production specific for a PBS extract of B. pahangi (BpA) by cells from infected and uninfected lymph nodes and by PBL. Five of 10 dogs were negative for proliferative responses to BpA in node cells from infected limbs, yet they had positive PBL responses, and another was negative in both node cells and PBL. Production of BpA-specific antibody was detected in cultures of node cells from infected limbs of 9 of 10 dogs, but only in two cultures of node cells from uninfected limbs and not at all in PBL cultures. Three dogs with responsive node cells produced the least amount of anti-BpA antibody in culture. Injections of B. pahangi adult worm excretory/secretory products (ES), totaling 1 mg over 48 h, into the limb of the original infections in seven dogs, resulted in inhibition of Ag-driven proliferation by cell populations previously responsive to BpA. There was a loss of PBL responsiveness by all but one infected dog and a loss of node cell response by the two dogs previously responsive in infected and uninfected nodes. This loss of responsiveness lasted at least 28 days in three dogs. There was no evidence of suppression of responses to mitogens either before or after ES injection. In contrast, BpA-specific antibody production was greatly increased in node cells from infected limbs injected with ES. Similar injections into the uninfected limbs of two infected dogs produced no change of proliferative responses or of antibody production in the uninfected node. These results indicate that ES can modulate immune cell, Ag-driven proliferation, and simultaneously enhance antibody production in previously infected nodes. This may promote parasite survival by inhibiting cellular attack based on delayed-type hypersensitivity while directing immune responses toward production of antibodies that are less damaging to the adult helminth.