This is consistent with our observation that tph-1(mg280) and tph-1(n4622) animals grown on lawns contaminated with 0.05% M. nematophilum have a larger percentage of Dar animals than wild type controls and suggests that TPH-1 activity in wild type animals inhibits the immune response triggered by infection by M. nematophilum. This evidence concerns the gene TPH1 and infection.