Co-infection with Trypanosoma cruzi protects mice against early death by neurological or pulmonary disorders induced by Plasmodium berghei ANKA

Abstract

Objective: The objective of this study was to investigate whether the infection of C57BL/6 mice by P. berghei ANKA, which causes severe malaria, was modulated by co-infection with Trypanosoma cruzi.

Methods: Groups of C57BL/6 mice were infected either with P. berghei ANKA, T. cruzi strain G, or with both parasites. The presence of parasites was checked by microscopic examination of blood samples. Symptoms of neurological or respiratory disorders, as well as mortality, were registered. Breakdown of the blood brain barrier was determined by injecting the dye Evans blue. Histological sections of the lung were prepared and stained with hematoxilin-eosin.

Results: All mice infected only with P. berghei ANKA died within 7-11 days post-infection, either with symptoms of cerebral malaria or with respiratory abnormalities. The animals co-infected with T. cruzi strain G survived longer, without any of the referred to symptoms. Protection against the early death by severe malaria was effective when mice were given T. cruzi 15 days before P. berghei inoculation. Breakdown of the blood brain barrier and extensive pulmonary oedema, caused by malaria parasites, were much less pronounced in co-infected mice. The degree of protection to severe malaria and early death, conferred by co-infection with T. cruzi, was comparable to that conferred by treatment with anti-CD8 antibodies.

Conclusion: Co-infection with T. cruzi protects C57BL/6 against the early death by malaria infection, by partially preventing either the breakdown of the blood brain, and cerebral malaria as a consequence, or the pulmonary oedema.

Figure 1

Mortality and course of infection in mice infected with P. berghei ANKA and/or T. cruzi G strain. Of three groups of C57BL/6 mice from the same batch, two were inoculated with T. cruzi metacyclic forms. Fifteen days later, P. berghei-parasitized erythrocytes were given to the uninfected (n = 6) and to one of the T. cruzi-infected group (n = 7), whereas one group remained infected with T. cruzi only (n = 6). A) Note the increased survival time in co-infected mice, as compared to the group infected with P. berghei only. B) Parasitaemia of P. berghei is expressed in percentage of parasitized erythrocytes and the values indicate the means ± SD. C) T. cruzi parasitaemias of individual mice are shown. Shown are the representative data from a set of experiments.

Figure 2

Breakdown of blood brain barrier in mice infected with P. berghei ANKA or co-infected with T. cruzi. C57BL/6 mice were separated in 4 groups, two of which were inoculated with T. cruzi G strain. Fifteen days later, one uninfected (n = 5) and one T. cruzi-infected group (n = 5) were inoculated with P. berghei ANKA, whereas one group remained uninfected (n = 3). When P. berghei-infected mice showed signs of neurological disorder, they were given the Evans blue and 1 h later the brain was removed. At this time, the corresponding number of mice in other groups received the dye and the brain was collected 1 h later. Note the difference of brain color in the three groups. The brains of the group with single T. cruzi infection (n = 5) (not shown) were indistinguishable from the normal mice.

Figure 3

Pulmonary oedema induced in mice infected with P. berghei ANKA or co-infected with T. cruzi. C57BL/6 mice were separated in three groups, two of which were inoculated with T. cruzi G. strain. Fifteen days later, one uninfected (n = 5) and one T. cruzi-infected group (n = 5) were inoculated with P. berghei ANKA, whereas one group remained uninfected (n = 3). When P. berghei-infected mice died from respiratory disorder, their lungs were collected for histological preparations and staining with hematoxilin-eosin. At this time, the corresponding number of mice in the co-infected group had also their lungs removed for histological sections and staining. Uninfected controls were subjected to the same procedure.

Figure 4

Effect of anti-CD8 antibodies on the mortality and course of infection in mice infected with P. berghei ANKA or co-infected with T. cruzi G strain. Of five groups of C57BL/6 mice, three were inoculated with T. cruzi metacyclic forms. Fifteen days later, P. berghei-parasitized erythrocytes were given to two uninfected groups (each n = 5), two T. cruzi-infected group (each n = 5), whereas one group remained infected with T. cruzi only (n = 5). On day 0 and 5 of malaria infection, one P. berghei-infected and one co-infected group were treated with anti-CD8 antibodies. B) Parasitaemia of P. berghei is expressed in percentage of parasitized erythrocytes and the values indicate the means ± SD.