Immunisation against East Coast fever: correlation between monoclonal antibody profiles of Theileria parva stocks and cross immunity in vivo.

Stocks of Theileria parva, which had been characterised by monoclonal antibody profiles, were used to challenge cattle previously immunised against East Coast fever (ECF). When cattle were subjected to homologous challenge, or heterologous challenge with a stock of identical profile to that which had initiated immunity, they showed mild or inapparent reactions. However, when cattle were challenged with a stock of a different profile many underwent severe or fatal ECF reactions. Thus, there appears to be good correlation between cross resistance patterns in vivo and parasite differences detected in vitro by monoclonal antibodies. The results indicate that monoclonal antibody profiles can be used to characterise strains of T parva in vitro, and thus provide valuable data for planning field immunisation programmes. Now that monoclonal antibodies offer the potential of characterising theilerial parasites so precisely, the need arises for more disciplined use of terms describing parasite populations and collections. It is proposed that the rules of nomenclature devised for trypanosomes be adopted for Theileria species.