Histological appearance of the site of inoculation and lymph nodes of guinea-pigs at various times after infection with Leishmania enriettii

Abstract

An investigation was undertaken to determine the immunological response of guinea-pigs to Leishmania infection through observation of the histology at the site of infection and regional lymph nodes of immune and normal animals at various intervals following inoculation with L. enriettii. Determinations of the leishmania growth-inhibitory activity of the animals' plasma were made concurrently. One day following challenge the immune guinea-pigs showed a marked inflammatory response at the site of infection whereas the normals did not. In the immune animals, the cell population at the infection site consisted of macrophages, plasma cells, eosinophils and lymphocytes, while in the normal animals, macrophages were the predominant cell type observed. Cell infiltration in the paracortical areas of the draining lymph node started on the third day and gradually increased until the sixth week of infection. A gradual and steady development of the germinal centres in the draining lymph nodes of the infected guinea-pigs began after the second week and reached a maximum after the sixth to eighth week of infection. Methyl green pyronin staining of the lymph nodes demonstrated many large pyroninophilic cells in the germinal centres and a few in the paracortical area. The leishmania growth-inhibitory factor was first detected in the plasma on the 44th day after infection and increased up to the 60th day.