Experimental toxoplasmic lymphadenopathy in rabbits.

The pathogenesis of toxoplasmic lymphadenopathy was studied in rabbits. Sixteen were infected with a high virulence strain of and 32 with one of low virulence. The former group were killed and examined at intervals up to 9 days and the latter up to 129 days. The high virulence strain quickly caused paracortical hyperplasia but only moderate follicular reaction. Later, lymphoid depletion occurred. The low virulence strain caused follicular reaction so that at 16 days germinal centres had developed with evidence of cellular phagocytosis. Histiocytes were present and plasma cells were found in the medullary cords. These appearances were seen up to 51 days. At 86 days the follicular reaction was no longer present but had returned at 129 days. These results were supplemented by serological, parasitological, immunofluorescence and electron microscopic data. The histological changes seen in the low virulence infections up to 51 days are unlike those caused by the high virulence strain but closely parallel those found in acquired infections in man, which are usually caused by strains of the low virulence type. These findings may help to elucidate the nature of the complex immune responses and the pathogenesis of toxoplasma infections.