Changes in splenic melano-macrophage centres of dab Limanda limanda during and after infection with ulcer disease

Splenic melano-macrophage centres (MMC) and assoc~ated parenchymic structures were compared in 3 groups of dab L r n a n d a limanda L from the North Sea healthy fish, flsh w t h ulcers, and fish w t h healed ulcers still recognizable as scars on the body surface Dab with open ulcers showed enlarged splenic MMC somewhat reduced in frequency and with increased haemosiderm content Dunng thls stage of infechon the density of pigmented granules .inthinMMC was reduced In favour of homogeneously scattered cells or a centrally located aggregation of cells all of which lacked phagocyhc inclusions Leucocytes were accumulated to an elevated degree around s p l e n ~c c a p ~l l a n e s Because of the reduced occurrence of single pigment-bearing cells in the splenic parenchyma and the very regular, rounded shape of the MMC, it is thought that during this stage of the d ~s e a s e the turnover rate In formahon and destruchon of MMC was diminished On the other hand, the increase in seemingly nonphagocyhc leucocytes in the MMC indicates a possible augmentahon of the humoral immune response After healing of the ulcers all splenic changes accompanying infechous c o n d ~h o n s regressed However, a return to the normal picture seen in healthy f ~s h did not occur as long as scars were still vlslble in the skin