Characterization of humoral and cell-mediated immunity in rabbits orally infected with Encephalitozoon cuniculi

Abstract

Encephalitozoonosis is a common infectious disease widely spread among rabbits. Encephalitozoon cuniculi, is considered as a zoonotic and emerging pathogen capable of infecting both immunocompetent and immunocompromised hosts. The aim of the study was to describe in detail the spread of the E. cuniculi in a rabbit organism after experimental infection and the host humoral and cellular immune response including cytokine production. For that purpose, healthy immunocompetent rabbits were infected orally in order to simulate the natural route of infection and euthanised at 2, 4, 6 and 8-weeks post-infection. Dissemination of E. cuniculi in the body of the rabbit was more rapid than previously reported. As early as 2 weeks post-infection, E. cuniculi was detected using immunohistochemistry not only in the intestine, mesenteric lymph nodes, spleen, liver, kidneys, lungs and heart, but also in nervous tissues, especially in medulla oblongata, cerebellum, and leptomeninges. Based on flow cytometry, no conspicuous changes in lymphocyte subpopulations were detected in the examined lymphoid organs of infected rabbits. Cell-mediated immunity was characterized by ability of both CD4 + and CD8 + T cells to proliferate after stimulation with specific antigens. Th1 polarization of immune response with a predominance of IFN-γ expression was detected in spleen, mesenteric lymph nodes and Peyer's patches. The increased expression of IL-4 and IL-10 mRNA in mixed samples from the small intestine is indicative of balanced control of IFN-γ, which prevents tissue damage. On the other hand, it can enable E. cuniculi to survive and persist in the host organism in a balanced host-parasite relationship. The Th17 immunity lineage seems to play only a minor role in E. cuniculi infection in rabbits.

A multidisciplinary review about Encephalitozoon cuniculi in a One Health perspective

“…After infection, the host compromised cells induce the release of Th1 cytokines, such as interleukin 12 (IL-12) and interferon gamma (IFN-γ), establishing an immune response mediated by CD8 + T cells, which leads to the destruction of the infected cells, through the perforin pathway (Khan et al 2001 ). Moreover, the proliferation of CD4 + cells is also described as part of the cell-mediated immunity (Sak et al 2017 ; Jeklova et al 2020 ) and, although with lesser protective effect, humoral immunity through the production of immunoglobulins against this pathogen is also present (Jeklova et al 2020 ). In fact, it seems that higher antibody titers are related to the acute phase of infection since a more accentuated spore multiplication is expected at this stage (Levkutová et al 2004 ; Wagnerová et al 2013 ).…”

“…In addition to organs and tissues, nested or real-time PCR has been also carried out in animals and humans using samples from feces (Deplazes et al 1996 ; Weber et al 1997 ; Fournier et al 2000 ; Lobo et al 2003 ; Sak et al 2011a ; Sak et al 2011b ; Perec-Matysiak et al 2019 ), urine (Deplazes et al 1996 ; Fournier et al 2000 ; Baneux and Pognan 2003 ; Csokai et al 2009 ; Hein et al 2014 ; Zietek et al 2014 ; Abu-Akkada et al 2015a ; Boer et al 2021 ), and cerebrospinal fluid (Csokai et al 2009 ; Hein et al 2014 ; Jeklova et al 2020 ), allowing the diagnosis of the disease in clinical cases and the identification of infected animals excreting spores in epidemiological prevalence surveys. The PCR technique in urine (Baneux and Pognan 2003 ; Csokai et al 2009 ) and in cerebrospinal fluid (Csokai et al 2009 ; Jeklova et al 2020 ) has been associated with low sensitivity, which can lead to false negative results. The currently accepted reason for the low sensitivity of this molecular screening method on urine samples is the intermittent excretion of spores, which decreases during the course of the infection (Cox et al 1979 ).…”

“…In addition, immunohistochemistry has been used mainly through monoclonal anti- E. cuniculi antibodies in tissue sections obtained from suspected animals (Mo and Drancourt 2004 ; Maestrini et al 2017 ; Jeklova et al 2020 ).…”

Advancement in our understanding of immune response against Encephalitozoon infection

“…However, CD4 + T cell deficiency does not alter the CD8 + T cell response against E. cuniculi infection, suggesting that CD4 + T cells are not the only activator of CD8 + T cell response 97,106 . Recently, Jeklova et al characterized the ability of both CD4+ and CD8+ T cells to proliferate after stimulation with E. cuniculi 107 . Th1 polarization with predominance of IFN‐γ expression was detected in spleen, mesenteric lymph nodes and Peyer's patches.…”

“…both CD4+ and CD8+ T cells to proliferate after stimulation with E. cuniculi 107. Th1 polarization with predominance of IFNγ expression was detected in spleen, mesenteric lymph nodes and Peyer's patches.…”