The above findings are not likely to be caused by differences in the MHC repertoire of the rat and rabbit strain used, since both strains used were outbred, reducing the likelihood that all of the individual rats and none of the rabbits induced functional antibodies. In addition, fair levels of antibodies was induced against the recombinant form of DBL4e in rabbits, indicating appropriate T-cell responses during the immunizations, yet the DBL4e specific rabbit sera was non-inhibitory even at rather high concentrations. Differential induction of binding-inhibitory antibodies is probably caused by species-specific differences in immuno-dominance of Bcell epitopes in different species of animals, similar to observations with antigens from other organisms [29, 30] . Responses to FV2 appeared more homogenous between species, at least with respect to the adhesion blocking properties, possibly due to presentation of more epitopes in a native form compared to single domains. Since the VAR2CSA molecule appears partly globular, immunodominant B-cell epitopes, not present in the native protein, may be exposed in individual DBL domains. This could also be the cause of the finding that antibodies induced against the DBL1X and DBL3X single domains, when based on heterologous sequences, can inhibit the binding of FCR3-IE [17] , as opposed to antibodies induced against DBL1X and DBL3X, based on the FCR3 sequence [15] .