The spleen of the H5N1-infected animals presented with very pronounced accumulation of Mac387-positive cells, mainly neutrophils, in the red pulp, most notably on days 1 and 2 pi (Fig. 2) and then decreasing, but not completely disappearing, over the following 5 days. Small numbers of scattered virus-antigen-positive cells were detected in the spleen of H5N1-infected animals on days 1 and 2 pi, but not in any of the other groups, where the spleen morphology tended to follow that of the lymph nodes, reflecting immune stimulation. The occurrence of CD83-positive cells also followed the pattern of the lymph nodes in these latter groups.