Antigenic peptides on the surface of Dirofilaria immitis microfilariae

Various methods of radioiodination were employed to identify peptides on the surface of Dirofilaria immitis microfilariae. Optimum surface radiolabelling occurred with the lactoperoxidase-catalyzed reaction. Two major peptides of 16 and 14 kDa were labelled by this method. These peptides were soluble in Nonidet P-40, were not glycosylated, and showed no signs of disulfide linkages. These peptides were immunoprecipitated by sera from D. immitis-infected dogs, but not by sera from uninfected dogs or sera from dogs with potentially cross-reactive nematode infections. Analysis of the 14 and 16 kDa peptides by two-dimensional gel electrophoresis revealed that the 16 kDa peptide was a single unit with a pI of 5.25 whereas the 14 kDa band was composed of three individual peptides with pI values ranging from 5.6 to 6.1. Iodination by chloramine T resulted in the same panel of labelled peptides but suffered from poor efficiency of ¹²⁵I incorporation. The viability of microfilariae labelled by the standard Bolton-Hunter method decreased by 50% following the reaction which resulted in the labelling of a variety of internal components.