Apicomplexan co-infections impair with phagocytic activity in avian macrophages

Abstract

Mixed infections of Toxoplasma gondii and Eimeria tenella are likely to occur frequently due to the high prevalence of both pathogens in free-ranging chickens. In this study, we investigated the co-occurrence of the two parasites in the same immune-competent host cell towards altered patterns of parasite-host interactions. Chicken blood monocyte–derived macrophages were co-infected with T. gondii RH tachyzoites and E. tenella Houghton sporozoites in vitro for 24 h. Through monitoring the uptake of pH-sensitive pHrodo™ Zymosan BioParticles (“Zymosan”) by macrophages, we created a three-dimensional model and to analyze quantitatively phagocytosis using confocal laser scanning microscopy. Assessments of parasite populations were performed by qPCR at 2, 6, 12, and 24 h post-infection (hpi). At 6 hpi, phagocytosis was inhibited in the E. tenella–infected cultures while no inhibition of phagocytosis was observed due to T. gondii. Phagocytosis activity revealed more complex interactions during co-infection. At 12 and 24 hpi, phagocytosis response to “Zymosan” was distinctly weaker in co-infected cells than in all other groups except for cells mono-infected with high doses of E. tenella at 24 hpi. By qPCR, significantly reduced numbers of both intracellular parasites were recorded (10-fold) in all infected groups at 2 hpi. At 12 hpi, the T. gondii population reached lowest values but dramatically increased by 24 hpi. Our data confirm that macrophage phagocytosis is involved in the control of invasion by apicomplexan parasites in chicken which particularly applies to E. tenella infection and it was able to be altered by the co-existing parasites.

Monocyte-Derived Chicken Macrophages Exposed to Eimeria tenella Sporozoites Display Reduced Susceptibility to Invasion by Toxoplasma gondii Tachyzoite

“…Compared to group Tg, tachyzoites showed significant motility differences ( p < 0.05) at the beginning (10 min) and after 80 min post infection (80, 90 and 110 min), and significantly lower DNA copy numbers ( p < 0.05) by qPCR at 2 hpi. In our previous study, only about 10% of applied tachyzoites were able to enter macrophages after T. gondii mono-infection at 2 hpi [ 25 ]. It may indicate that most tachyzoites stay extracellular or adherent when alive, which is similar with our microscopy observation.…”

“…A previous study showed that asexual stages of T. gondii , E. acervulina and E. tenella displayed ultrastructural similarities [ 24 ]. In addition, macrophage phagocytosis was distinctly altered during in vitro co-infection by T. gondii and E. tenella in our recent study [ 25 ]. Thus, we are particularly interested in studying whether the capacity of T. gondii to invade and survive in macrophages is affected by host-specific E. tenella infection.…”

Interplay between Eimeria acervulina and Cryptosporidium parvum during In Vitro Infection of a Chicken Macrophage Cell Line (HD11)

“…Zhang et al [ 40 , 41 ] provided quantitative data during single and coinfection of E. tenella and Toxoplasma gondii in peripheral blood macrophages. E. tenella numbers were constantly reduced at all timepoints examined (2, 6, 12, and 24 hpi) in coinfected cultures [ 41 ]. Interestingly, the same authors measured the replication of E. tenella in poultry macrophages at 24, 48, and 72 hpi.…”

“…Other possible explanations for this discrepancy could be the different immunogenic potentials across Eimeria species [ 43 ], or the difference in MOI between studies. We used a lower MOI than Zhang et al, which may have impacted the macrophage response [ 40 , 41 ].…”

“…Zhang et al [ 41 ] discovered that the phagocytic activity of the infected macrophages was hindered at 6 hpi for E. tenella infection but not for T. gondii . This could explain the peak in parasite replication we observed at 6 hpi in almost all cohorts of our study; the increment in intracellular E. acervulina at 6 hpi could have been the product of active cell invasion instead of phagocytosis.…”