T cell response to an MHC-II restricted epitope of rodent malaria

Abstract

Malaria is caused by different <em>Plasmodium</em> species that can infect a variety of animals including humans and rodents. The life cycle of these parasites is complex and includes a liver stage followed by a blood-stage in their vertebrate hosts. While the host’s immune response against each of these stages is incompletely understood, CD4 T cells are known to play an important role in immunity to <em>Plasmodium infection</em> during both stages. This project aims to examine the specific CD4 T cell response to a novel MHC II-restricted epitope in <em>Plasmodium infection</em> in C57BL/6 <em>mice</em>, and to characterise the protective capacity of these T cells. To this end, we made use of a recently generated TCR transgenic mouse line, termed PbT-II, which responds to a so far unknown <em>Plasmodium</em> derived epitope. In this project, the PbT-II epitope was identified as derived from heat shock protein 90, residues 484 to 496 (Hsp90_484-496 or abbreviated DIY). Different priming methods, such as injection of an anti-Clec9A antibody attached to the Hsp90 epitope (&#945;Clec9A-DIY), infection with <em>P. berghei</em> ANKA (PbA) infected red blood cells (iRBCs) or immunisation with radiation attenuated PbA sporozoites (RAS), were used to characterise PbT-II memory cell formation. Results revealed the formation of memory PbT-II cells expressing surface markers associated with central memory T cells (T_CM), effector memory T cells (T_EM) and tissue resident memory T cells (T_RM). Given the importance of tissue-resident memory T cells in peripheral immunity, mainly studied in CD8 T cells, we focused our study on the formation and function of CD4 T_RM cells in the liver. Parabiosis studies using RAS vaccinated mice confirmed the liver residency of a CD69⁺ PbT-II cell population. Gene expression profile analysis revealed that these CD4 T cells expressed a core gene signature similar to that of CD8 resident memory T cells. Furthermore, differences in the gene expression profile of PbTII T_RM cells generated via different protocols, suggested lineage specific effector mechanisms, such as IL-4 production or perforin expression, for subsets of CD4 T_RM cells in the liver.