Cytotoxic Innate Intraepithelial Lymphocytes Control Early Stages of Infection

Background: Intraepithelial lymphocytes (IELs) are the first immune cells to contact and fight intestinal pathogens such as , a widespread parasite which infects the gut epithelium. IFN-γ producing CD4 T IELs provide an efficient and a long-term protection against cryptosporidiosis while intraepithelial type 1 innate lymphoid cells limits pathogen spreading during early stages of infection in immunodeficient individuals. Yet, the role of T-cell like innate IELs, the most frequent subset of innate lymphocytes in the gut, remains unknown.

Methods: To better define functions of innate IELs in cryptosporidiosis, we developed a co-culture model with innate IELs isolated from mice and 3D intestinal organoids infected with using microinjection.

Results: Thanks to this original model, we demonstrated that innate IELs control parasite proliferation. We further showed that although innate IELs secrete IFN-γ in response to , the cytokine was not sufficient to inhibit parasite proliferation at early stages of the infection. The rapid protective effect of innate IELs was in fact mediated by a cytotoxic, granzyme-dependent mechanism. Moreover, transcriptomic analysis of the Cryptosporidium-infected organoids revealed that epithelial cells down regulated Serpinb9b, a granzyme inhibitor, which may increase their sensitivity to cytolytic attack by innate IELs.

Conclusion: Based on these data we conclude that innate IELs, most likely T-cell-like innate IELs, provide a rapid protection against infection through a perforin/granzymes-dependent mechanism. infection. The infection may also increase the sensitivity of intestinal epithelial cells to the innate IEL-mediated cytotoxic attack by decreasing the expression of Serpin genes.