Predominance of infected reticulocytes in the peripheral blood of CD4+ T-cell-depleted mice chronically infected with Plasmodium chabaudi chabaudi.

The distribution of Plasmodium chabaudi chabaudi AS among normocytes and reticulocytes in the peripheral blood of NIH mice undergoing a primary infection was determined from brilliant cresyl blue/Giemsa's stained thin blood films. During the early stages of infection in normal mice, parasites were found exclusively in normocytes. The presence of parasites in reticulocytes was limited to a period of severe immune pressure on the parasites, peak parasitaemia and the ensuing "crisis" phase, at which time the rapid production of new erythrocytes in response to the anaemia in these mice resulted in a high reticulocyte count. Later, during the recrudescence, parasites inhabited normocytes only. Thus, in immunologically competent animals, P. c. chabaudi AS showed no absolute preference for either mature or immature erythrocytes. In marked contrast, in chronically infected CD4+ T-cell-depleted mice, this malaria parasite apparently displayed a pronounced predilection for reticulocytes. During an unremitting parasitaemia of 2.8%-3.9% during days 13-60 post infection, all parasites were found in reticulocytes, even though these comprised only 25% of the total erythrocyte count. The possible reasons for this reversal in preference for the type of erythrocyte inhabited by asexual malaria parasites are discussed.