Evaluation of between-host heterogeneity in the patterns of immune gene expression in Hepatocystis parasite-infected African epauletted fruit bats

Abstract text

Hepatocystis parasites are the closest relatives of the mammalian Plasmodium species. The genus currently contains up to 25 known species. Hepatocystis parasites are known to infect Old World mammals and are most prevalent in bats and nonhuman primates. The life cycle of Hepatocystis differs to that of Plasmodium by the fact that no multiplication of parasites occurs in the blood. Furthermore, parasites of Hepatocystis develop macroscopically visible characteristic merocyst stages in the liver of their hosts, in which the parasites multiply asexually, resulting in large numbers of merozoites that are released into the blood stream. The parasite infections are considered as benign. A previous study analyzing the draft genome and transcriptome of a primate Hepatocystis species found evidence for the loss of blood schizogony in Hepatocystis parasites.

In this study we investigate the between-host heterogeneity in the patterns of gene expression in Hepatocystis-infected African fruit bats of the species E. labiatus in Northern Uganda. Blood, liver, and spleen samples were collected from 114 bats. We analysed 3´-Tag RNA-Seq data from liver and spleen tissues from Hepatocystis-blood stage positive and uninfected bats. Differential gene expression analyses were carried out to investigate potential differences in gene expression regarding season and sex, age, reproductive status, and infection status of the bat hosts. We aim to identify host genes that are differentially expressed in the liver and in the spleen and determine their functions and roles they might play in the bat host immune response to infections with Hepatocystis parasites and compare our findings to Plasmodium infections in mammals.

The preliminary data revealed a high number of differentially expressed transcripts (DETs) for the parameters host age and breeding status. The letter could point to an impact of Hepatocystis infections on the host during periods of stress (such as breeding season). Higher numbers of DETs were also recovered in the spleen tissue, where immune genes in the host are active. Interestingly, blood stage parasitemia did not correlate with host gene expression, neither in the liver nor in the spleen.