The early intestinal immune response in experimental neonatal ovine cryptosporidiosis is characterized by an increased frequency of perforin expressing NCR1(+) NK cells and by NCR1(-) CD8(+) cell recruitment.

Line Olsen,Fabrice Laurent,Preben Boysen,Arild Espenes,Timothy Connelley,Caroline Åkesson,Coralie Metton,Sonia Lacroix-Lamandé,Françoise Drouet,Anne K Storset

doi:10.1186/s13567-014-0136-1

Abstract

Cryptosporidium parvum, a zoonotic protozoan parasite, causes important losses in neonatal ruminants. Innate immunity plays a key role in controlling the acute phase of this infection. The participation of NCR1+ Natural Killer (NK) cells in the early intestinal innate immune response to the parasite was investigated in neonatal lambs inoculated at birth. The observed increase in the lymphocyte infiltration was further studied by immunohistology and flow cytometry with focus on distribution, density, cellular phenotype related to cytotoxic function and activation status. The frequency of NCR1+ cells did not change with infection, while their absolute number slightly increased in the jejunum and the CD8+/NCR1- T cell density increased markedly. The frequency of perforin+ cells increased significantly with infection in the NCR1+ population (in both NCR1+/CD16+ and NCR1+/CD16- populations) but not in the NCR1-/CD8+ population. The proportion of NCR1+ cells co-expressing CD16+ also increased. The fraction of cells expressing IL2 receptor (CD25), higher in the NCR1+/CD8+ population than among the CD8+/NCR1- cells in jejunal Peyer’s patches, remained unchanged during infection. However, contrary to CD8+/NCR1- lymphocytes, the intensity of CD25 expressed by NCR1+ lymphocytes increased in infected lambs. Altogether, the data demonstrating that NK cells are highly activated and possess a high cytotoxic potential very early during infection, concomitant with an up-regulation of the interferon gamma gene in the gut segments, support the hypothesis that they are involved in the innate immune response against C. parvum. The early significant recruitment of CD8+/NCR1- T cells in the small intestine suggests that they could rapidly drive the establishment of the acquired immune response.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-014-0136-1) contains supplementary material, which is available to authorized users.

Highlights

As with all neonatal mammals, the new-born ruminant is challenged by infections at vulnerable mucosal sites like the gut mucosa, frequently leading to enteritis
The early immune response of neonatal ruminants to C. parvum infection is still largely unknown some insight has been gained on the recruitment of CD8 lymphocytes by Wyatt et al [10,52] and of mast cells by Li et al [53] in the gut of infected calves
Various recent studies on innate immune cells in mice and humans led to the discovery that NCR1+ cells include conventional Natural Killer (NK) cells and innate lymphoid cells (ILC) of groups 1 and 3 [56]

Summary

Introduction

As with all neonatal mammals, the new-born ruminant is challenged by infections at vulnerable mucosal sites like the gut mucosa, frequently leading to enteritis. To develop an adequate immunoprophylaxis strategy, it is important to clarify the early immune events leading to a protective response against this parasite as neonates frequently become infected within the few hours following birth. Limited information is available on the neonatal ruminant intestinal immune response to C. parvum during the early stages of the infection. Pathogenicity and brief pathology of ovine cryptosporidiosis were described in lambs for the first time [1,2,7] more than three decades ago and more recent data were obtained in calves describing the intestinal response to the parasite with an increase of T cell subsets [8,9,10,11,12]. Our understanding of the immuno-pathological response to C. parvum remains poor in these species

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