Dendritic leucocytes as possible carriers of murine Plasmodium merozoites. Preliminary note.

A merozoite of Plasmodium yoelii nigeriensis was observed, by transmission electron microscopy, associated with the surface of a dendritic leucocyte, in the cortical zone of a renal lymph node from a heavily infected mouse. En microscopie électronique, un mérozoïte de Plasmodium yoeli nigeriensis a été trouvé associé à la surface d'une cellule dendritique dans la zone corticale d'un ganglion lymphatique rénal d'une souris très infectée. Observations with murine malaria parasites (reviewed by Landau and Chabaud, 1994) indicate that some merozoites do not enter the red blood cells immediately after their release from mature blood schizonts. It was hypothetized that they leave the bloodstream and enter the lymphatic system, where they remain for variable lengths of time. The discovery of malaria parasites in the lymphatic circulation (Landau et al., 1995) confirmed this hypothesis. Furthermore, observations by Deharo et al., 1995, showed that variations of the lymphatic flux, such as a post prandial increase, have an impact on the parasitaemia of Plasmodium yoelii nigeriensis. In this report we present an interesting finding of a P. y. nigeriensis merozoite associated with the surface of a dendritic leucocyte, observed by transmission electron microscopic examination of the renal lymph node from a heavily infected mouse. A male Swiss mouse (478 LN) IOPS-OF1 (Iffa-Credo, France) weighing 20 g was inoculated intraperitoneally with blood from a mouse infected with P. y. nigeriensis. Four days post-inoculation , when parasitaemia reached 30 %, the mouse was autopsied and the renal lymph node was processed for electron microscopy studies. ELECTRON MICROSCOPY The renal lymphatic node was cut into 1 mm 3 pieces, which were fixed at room temperature for 60 minutes, in a 2.8 % glutaraldehyde solution in a 0.1 M Sorensen phosphate buffer (pH = 7.4), washed twice in the buffer and post-fixed 60 minutes, in a 2 % osmium tetroxide solution in the same buffer. Potassium ferricyanide was added to both fixatives. The samples were then stained for 12 hours in 0.5 % uranyl acetate in distilled water. Following dehydration, the material was embedded in a 1:1 mixture of Araldite-Epon®. Sections were stained with uranyl acetate and lead citrate for examination with a PHILIPS EM 201 at the Centre Inter-universitaire de Microscopie Electronique-Jussieu Paris VI. Fig. 1.-Partial vue of the cortical zone of a renal lymph node showing a merozoite (arrow) at the surface of a dendritic cell characte­ rized by two long pseudopodia (arrow-heads) a clear cytoplasm; …