The temporal sequence of morphological changes occurring in the prefemoral lymph nodes of sheep experimentally infected with Trypanosoma brucei was studied at weekly intervals during the course of infection.
Histopathological changes started with lymphoid stimulation which was soon overtaken and masked by intense proliferation of reticulo-endothelial cells. Reticulo-endothelial proliferation resulted in macrophage accumulation, some vascular damage and lymph stasis, varying from insidious to extensive. Reticulo-endothelial activity subsequently decreased and there was an upsurge of proliferative activity in lymphoid tissue. Lymphoid stimulation resulted in increased numbers of primary follicles with active germinal centres and produced cells primarily lymphoblast/plasmablast in type. The response appeared to involve blast cells of the germinal centres rather than thymus-dependent paracortical areas. Both reticulo-endothelial and lymphoid components exhibited marked cellular necrosis which increased throughout the course of infection. Intense lymphopoiesis was not correlated with lymphocytosis but was associated with lymphopaenia.