Fig. 1. Mean proportional increases in OVA-specific antibody titres versus time after primary immunisation.

Standard deviations around the mean are shown for both experimentally-immunised tortoises (n = 16) and procedural control animals (n = 4). Due to variable levels of pre-immunisation NAbs to OVA among animals, the proportional increase in antibodies for each animal is (Ab titre at time x)/(pre-immunisation NAb titre).