Frequency of SIV RNA positive cells in protected, superinfected vaccinates and challenge controls by in situ hybridisation.

All vaccinates were challenged with the same dose of SIVsmE660 for the same duration (20 weeks); the total time to sampling is indicated by the vaccination duration of 20 or 3 weeks and group (A–C). The frequency of SIV positive (+ve) cells determined by in situ hybridisation (ISH) is shown for each tissue. Lymphoid tissues sampled were spleen (Spl), peripheral and mesenteric lymph nodes (PLN, MLN), small intestine (S.Int) and thymus (Thy) collected post-mortem. A grading system of + (0.5–6.8), ++ (6.9–13.8) and +++ (>13.8) cells/mm3 was employed.