An early intestinal mucosal source of gamma interferon is associated with resistance to and control of Cryptosporidium parvum infection in mice

Abstract

Resistance to and control of Cryptosporidium parvum infection in mice in the absence of adaptive immunity appears to be gamma interferon (IFN-gamma) dependent. Using an IFN-gamma-neutralizing antibody in a murine model, we demonstrated increased susceptibility to infection within 24 h. We correlated this early resistance and control with increased mucosal expression of IFN-gamma and demonstrate that CD8+ T-cell receptor alphabeta intestinal intraepithelial lymphocytes express and secrete this cytokine shortly after infection. The rapid kinetics of IFN-gamma expression and secretion by naive CD8+ T cells in response to a protozoan pathogen have not previously been demonstrated.

FIG. 1.

IFN-γ neutralization increases the susceptibility of wild-type mice within 24 h after C. parvum infection. (a and b) Representative hematoxylin- and eosin-stained sections of terminal ileum taken 24 h after mice were infected with C. parvum. In panel b, the mouse received an intraperitoneal injection of anti-IFN-γ antibodies (XMG 1.2) 24 h prior to infection, and panel a shows the results with an untreated control. Black arrowheads indicate parasites. (c) Histogram depicting the mean number (+standard deviation) of parasites counted in histological sections from five mice per group (*, P = 0.0001). (d) Histogram showing samples from the same experiment quantified by real-time PCR. Each bar represents the mean number of copies of Cpgp40/15 normalized to the number of copies of nidogen (**, P = 0.001). Data are representative of two independent experiments.

FIG. 2.

Increased IFN-γ expression in the small intestines of mice 24 h after C. parvum infection. (a) Quantitative PCR demonstrating increased IFN-γ in the terminal ilea of C. parvum-infected mice compared with levels in sham-infected mice. Each bar represents mean copies of IFN-γ normalized to mean copies of GAPDH by quantitative PCR for five mice per group (*, P < 0.05). Data are representative of two independent experiments. (b) Increased IFN-γ expression in iIEL from infected compared with its expression in uninfected mice. Each bar represents IFN-γ normalized to GAPDH by quantitative PCR from pooled samples of two mice (*, P = 0.01). Data are the means from two independent experiments.

FIG. 3.

ELISA measuring IFN-γ secretion from ex vivo-sorted TCRαβ⁺ and TCRγδ⁺ CD8α⁺ iIEL from C. parvum-infected and sham-infected mice (*, P = 0.028). Data are representative of three independent experiments.