The cross-reactive immune response between infective larvae and adult worms of Acanthocheilonema (Dipetalonema) viteae is dominated by phosphorylcholine

Summary The immune response of BALB/c mice against living L3 or adult extract of Acanthocheilonema viteae induces three antibody populations, namely antibodies which cross-react between the two forms of A. viteae, and either (i)do, or (ii) do not express specificity for phosphorylcholine (PC), and (iii) antibodies which do not cross-react between the two stages. In the anti-L3 serum, almost all cross-reactive antibodies to adult antigen arc PC specific and of the IgM isotype, apart from a minor non-PC-reactive IgE response. On the other hand, the cross-reactive antibodies in the anti-adult scrum are not PC reactive and of the IgG3 isotype. The non-cross-reactive antibodies in the two sera were predominantly IgM and IgG2/IgG1 for the anti-L3 and anti-adult respectively. Immunofluorescence and immunocytochemical studies on third-stage larvae and female worms revealed that antigens expressing PC determinants were mainly found on certain internal structures, whereas the cuticles of adults and the outer cuticle part of L3 are PC negative. Topographical analyses revealed distinct differences in labelling patterns by the two antisera, in the different areas. Thus the cross-reactive and non-cross-reactive antibodies induced by BALB/c mice to the two stages of A. viteae are different in nature. Since the antibody response induced by the L3 form and cross-reactive to the adult form is directed towards an ubiquitous antigen, namely PC, which is not present on cuticula of either the L3 or adult worms, this response may not contribute to protection against the parasite.