Single-cell transcriptome uncovers heterogeneity and immune responses of leukocytes after vaccination with inactivated Edwardsiella tarda in flounder (Paralichthys olivaceus)

Abstract

From an evolutionary point of view, the immune system of poikilothermic vertebrates is special and mysterious, and its immunity depends on the conserved components and functional complexity of immune cells. Unraveling the diversity and functional differences of immune cells can contribute to efficient and scientific vaccinations. Here we established a model of formalin-killed Edwardsiella tarda vaccination within flounder (Paralichthys olivaceus), and investigated the classification, kinetic and immunity of leukocytes from head kidney by single-cell RNA sequencing. The sequencing results revealed that the leukocytes of flounder were divided into 12 clusters, including immune cells such as granulocytes, monocytes/macrophages, T/B lymphocytes, DCs and NK-like cells. The sub-classification was performed for granulocytes, monocytes/macrophages and T/B lymphocytes, in which B cells could be classified into naive B cells, activated B cells and antibody-secreting cells. The number of granulocytes, myeloid progenitor cells and hematopoietic stem cells increased after inactivated vaccine immunization, and the percentages of activated B cells and antibody-secreting cells also significantly increased. In addition, a positive correlation was found between the activation of B cells, secretion of specific antibodies and the protection efficacy of the inactivated vaccine. These results firstly provide a landscape of immune cells after vaccination in teleost fish, which shed new light on the development of efficient vaccines in aquaculture.