title: Plasma cells in the ammocoete of Petromyzon marinus.
abstract: This study demonstrates for the first time the presence of mature and developing plasma cells in the spleen of non-immunized ammocoetes of Petromyzon marinus. Plasmocytes occur as electron-dense cells with much condensed chromatin and an extensively large developed and dilated rough endoplasmic reticulum. The importance of this finding is emphasized in relation to the evolution of the immune system.
mesh_terms: D000818:Animals; D005399:Fishes / Q000254:growth & development*; D007798:Lampreys / Q000033:anatomy & histology / Q000254:growth & development*; D008854:Microscopy, Electron; D010950:Plasma Cells / Q000648:ultrastructure*; D013154:Spleen / Q000166:cytology*