ABSTRACT: The role of the liver for survival of blood-stage malaria is only fragmentary understood. In the experimental blood-stage malaria Plasmodium chabaudi, protective vaccination induces self-healing and, thus, survival of otherwise lethal infections. This study investigates the response of the liver, in terms of mRNA and lincRNA expression, to vaccination-induced self-healing infections and lethal P. chabaudi malaria at early patency on day 4 p.i., when parasitized erythrocytes begin to appear in peripheral blood. Using gene expression microarrays, 23 genes were identified to be induced in the liver by >10-fold at p<0.01. More than one third were genes involved in erythropoiesis, as e.g. Kel, Rhag, Ahsp, Ermap, Slc4a1, Cldn13 Gata1, and Gfi1b. Another group of >10-fold expressed genes contain genes involved in natural cytotoxicity, as those encoding the killer cell lectin-like like receptors Klrb1a, Klrc3, Klrd1, Ncr1 and the granzyme B encoding Gzmb. In addition, there were identified a series of genes involved in the control of cell cycle and mitosis, as Ccnb1, Cdc25c, Ckap2l expressed by >10-fold only in vaccination-protected mice, and 22 genes being at least 100% higher expressed in vaccination-protected mice than the corresponding genes significantly expressed in non-vaccinated mice. Furthermore, distinct lincRNA species were changed by >3-fold in livers of vaccination-protected mice, whereas lethal malaria induced different lincRNAs. Our data suggest that protective vaccination accelerates extramedullary erythropoiesis, generation of liver-resident cytotoxic cells, and regeneration from malaria-induced injuries in the liver at early patency, which may be critical for final survival of otherwise lethal blood-stage malaria of P. chabaudi. Mice: Balb/c mice breeded under specified pathogen-free conditions were delivered from central animal facilities of the University of Düsseldorf. The experiments were performed only with female mice aged 10-12 weeks. They were housed in plastic cages, received a standard diet (Woehrlin, Bad Salzuflen, Germany) and water ad libitum. This study was carried out in strict accordance with the German law on animal protection. The keeping of mice as well as the experimental protocol of the study were officially approved by the State-controlled Committee on the Ethics of Animal Experiments of the State Nordrhein-Westfalen, Germany, and were regularly controlled, without being previously announced, by the local authorities. All efforts were undertaken to minimize suffering of mice. P. chabaudi malaria infection: Blood-stage infections of P. chabaudi were kept in outbred mice under sterile conditions by weekly passages of infected blood. A non-clonal line of P. chabaudi is used in our laboratory since 1982, which resembles to P. chabaudi chabaudi. Challenge of Balb/c mice with 10^6 P. chabaudi-infected erythrocytes, Protective vaccination: As a vaccine, host cell plasma membranes were used, which were isolated in the form of ghosts from P. chabaudi-parasitized erythrocytes Approximately 10^6 ghosts were suspended in 100 µl Freund’s complete adjuvant (FCA) and subcutaneously injected on week 3 and week 1 before infecting with P. chabaudi-parasitized erythrocytes. Control mice were treated in parallel only FCA.
